Intermittent stall

Paul Technician Minnesota Posted   Latest  
Unsolved
Driveability
1994 Chevrolet C1500 Silverado 5.7L (K) 4-spd (4L60-E) — 1GCEK19K8RE235482
Intermittent Stall In Gear
Rough Idle

How hard can it be? Above truck came in as a rough idle, stalling in gear at low rpm. Replaced dist., had new tbi on it, cap rotor, plugs, IAC motor, intake gaskets. Although it runs much better if you do not lightly hold rpm's up it will stall in gear. It seems t stall when it has a very quick single missfire. No missfires show up on scanner. Also coil is new as well. Any help or direction is appreciated.

0
Interesting
Angelo Instructor
Missouri
Angelo
 

EGR System? Are you having a lean condition?

0
Ð Awarded
Keith Diagnostician
Louisiana
Keith
 

Start with simple basics. Check your timing is set correctly, base idle set and crank/cam reset (p1345). There can be a problem with IAC wiring connect having a broken wire. EGR valve partially stuck open. Problems also with crank sensor low amplitude at lower RPM.

+1
Ð Awarded
Agree
Matthew Diagnostician
Kentucky
Matthew
 

Will this vehicle stall out at all while driving off idle? when it stalls im assuming it restarts right away? did any of the parts make it run smoother at idle. fuel pressure? fuel trims? more info needed. Thx

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Trims are normal, fuel press @ 11 psi. Spec is 9-13. Will not stall when driving at all.

0
Ð Awarded
Gino Owner/Technician
Texas
Gino
 

Put a fuel pump in it - has to have at least 12 and a half coming out of the filter 13 is better

-1
Ð Awarded
Disagree
Rusty Owner/Technician
Massachusetts
Rusty
 

11PSI was quite normal for these.

0
Ð Awarded
Agree
Disagree
Darren Owner/Technician
Arkansas
Darren
 

True, but one does need to question whether or not the gauge is accurate. The difference between 35 and 38 psi is not nearly as different as between 11 and 13 psi in the overall volume/pressure calculations (as I remember) Periodically I do calibrate my gauges with 1 PSI being 2.03602 InHG. As a side comment, TPMS problems and explaining to that 1 customer who sees their dash display a 1 to 3…

0
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

Unrelated info He lacks extended crank and a code 44 so it’s not a fuel supply issue.

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
 

Exactly…

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Have tried timing @ 0*, 5 advanced, 5 retarded. Have removed & used a block plate on egr to no avail.

0
Ð Awarded
Boyd Technical Support Specialist
Georgia
Boyd
 

Was it set with the timing wire disconnected?

0
Ð Awarded
Dan Owner/Technician
Texas
Dan
 

… And verified that the crank dampener ring has not slipped from where it indicates TDC REALLY is… Dan H. … Hobbs.

+1
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

On this platform I don’t think that matters. Everything is in the distributor. No crank sensor

0
Ð Awarded
Dan Owner/Technician
Texas
Dan
 

… I realized that … thus … the OOPS ! … Dan H. … Hobbs

0
Ð Awarded
Scott Owner
California
Scott
 

No, you were right Dan. There is a base timing adjustment that depends on the mark on the balancer being at TDC. I’ve seen the balancer move - it’s isolated in rubber.

0
Ð Awarded
Obie Technician
Washington
Obie
 

Is the convertor locked up? That will stall it in gear. Also check and verify timing. Do a quick test to check TDC against the timing marks. The damper can rotate the outer hub if it is broken.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Engine will idle for long periods of time, but when it has a very rapid single miss it's like the engine cannot recover fast enough if that makes sense.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

IAC counts should be about 25-30 hot idle unloaded in Park. If lower, there's an issue with vacuum leaks or the throttle is too far open. If higher, then the IAC is trying to keep the system from stalling. EGRs were a constant problem on these way back when, but much more so on the Vortecs, which this is not, aside from which you've eliminated it. There are no misfire counts on pre-OBD2…

0
Ð Awarded
James Technician
Virginia
James
 

I know this sounds rudimentary, but has a cam/crank correlation relearn been performed on this since the parts were replaced? Lots of techs overlook it, and it can cause running issues if not performed after repairs.

0
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

I don’t think that’s possible on a 94. Theres no CKP Sensor on these IIRC

+1
Ð Awarded
Tom Owner/Technician
Tennessee
Tom
 

If this is a ‘94 and not a misprint, it is OBD I and there will be no misfires, no P1345’s, no relearn, etc. Check the coil wire for jumping to ground intermittently. And then I would scope one injector control side, the coil primary, and the signal from the dist. to the ECM. Tom

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

It is indeed a 94

0
Ð Awarded
Dan Owner/Technician
Texas
Dan
 

… Does it have an OBD II connector like a (say) 2004 Silverado would have ???… OR … an OBD I connector like (say) a 1988 Impala would have ??? … Dan H. … Hobbs … South Texas …

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Definitely obd 1

0
Ð Awarded
Nelson Diagnostician
North Carolina
Nelson
 

Be sure to check the small vac hose to the map sensor at the T body. I had a 95 C1500 a few years ago that came in with vac hose fallen off. Reconnected and it was the fix. Also, you might want to graph the TPS as you sweep it through it range to see if there are any drop outs as well

0
Ð Awarded
Dan Owner/Technician
Texas
Dan
 

… Paul … You said “ tried timing @ 0*, 5 advanced, 5 retarded.”… FYI … the “TIMING” is NOT adjustable… only the “cam retard” is… not with a timing light …but with a scan tool… Is this what you were speaking of ? … Dan H. … Hobbs. … South Texas …

0
Ð Awarded
Dan Owner/Technician
Texas
Dan
 

… OOPS … TBI …. nevermind…. Dan H. … Hobbs. …

0
Ð Awarded
William Owner/Technician
Kentucky
William
 

Is oil in the distributor? We used to see bad distributors do this quiet frequently. The shaft on the distributor was made without grooves and a new and improved shaft with grooves and a new pickup coil used to fix this problem. Also check for lateral play in the shaft.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

It is on it's 2nd reman dist. too.

0
Ð Awarded
Craig Diagnostician
Illinois
Craig
 

Paul, does this second remanufactured distributor use an older style HEI style pickup and pole piece? Probably the same as the first remanufactured I would suspect. If this is the case you will need to source the correct magnet shaft and pickup from GM if still available. The newer magnetic shaft and pickup design is able to produce a signal at hot idle low rpm, whereas the old HEI style cannot…

0
Ð Awarded
William Owner/Technician
Kentucky
William
 

You might want to check the grounds on the thermostat housing, also you should drop the ecm and tap test and wiggle the connectors to it. Is the tps smooth, we have had glitches in some of the older ones that would not set codes, what is integrator and block learn, check the coolant sensor for accuracy.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Cleaned & sanded grounds too. TPS sweep on labscope looks good too.

0
Ð Awarded
William Owner/Technician
Kentucky
William
 

Try unplugging the alternator, it may be pumping out ac, also check the main power feed from the alternator to the battery for breaks, we have seen these cause voltage spikes that the ignition module mistakes for ignition pulses.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Less than .1 peak to peak however I have not closely inspected the main feed. I will check that next. Thanks.

0
Ð Awarded
Rick Technician
New York
Rick
 

I remember a lot if the older GM’s would have bad wire(s) on the distributor pick up that had broken wires but appeared ok because the insulation didn’t break, but that usually acted up on acceleration when it flexed. You say the distributor was replaced, just make sure all the wiring is good inside and outside of the distributor.

0
Ð Awarded
Ken Owner/Technician
Arizona
Ken
 

Try and disconnect the timing bypass connector….does it run better…if so possible faulty module…also verify timing and balancer…after that if it is still rough you need to go back to basics….steady vacuum…compression test…ect….look for and engine issue…check for vacuum in the crankcase…I have seen vortex heads put on a aftermarket tbi intake manifold and the gasket are to thin and creating an…

0
Ð Awarded
Darren Owner/Technician
Arkansas
Darren
 

Sounds like you covered most of the typical causes but…. A few things you need to check. Go back like you have not seen it before. Does the IAC respond correctly, idle start up flare and comes back to base idle. Does the IAC respond to load? Have you put it in “Field Service Mode” to see if it stalls, holds idle etc? Exhaust condition, does it have any exhaust leaks? Any oil leaks into the…

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Paul, Try applying about 18-20Hg vacuum to the MAP with a handheld vacuum pump. Possibly a carbon choked MAP/ PCV port in the base of the TBI unit. These had lots of issues with carbon buildup and TBI base gaskets. Next idea that comes to mind is to measure the TPS at idle and do a sweep test with a meter to check for an issue there.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Again, if you've been following the thread at all Glenn, you'd already know that there is a new throttlebody on it! As the statement goes: “Asked and answered”!

+1
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

Based on your symptom, it sounds like you may be dealing with a wiring issue that causes an open or short as the engine vibration causes a harness to wiggle at a specific frequency. Maybe you’ve wiggled harnesses already but that’s what I’d be doing. The ECM is behind the glove box where mice like to nest. I’ve seen ECM wiring chewed and corroded so badly you’d wonder how the truck ran. Hope…

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Tried a reman ECM a few minutes ago, no difference.

0
Ð Awarded
James Technician
California
James
 

Check the PCV port on the throttle body. It can get clogged with carbon and cause your symptom.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Open. [new throttle body]

-1
Ð Awarded
Tad Owner/Technician
Florida
Tad
 

First, index the crank at TDC #1 to the 0* mark on the timing over and at the same time check the timing chain deflection - anything more than a very few degrees deflection is a problem but WILL NOT MAKE IT STALL… Next, warm it up, being sure the ECT and ACT temps are correct... Shut it down, discon the EST connector, discon the scanner, fire it up and set the base timing to spec at well under…

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Paul, Has the inline fuel filter been replaced? Fuel filters can create some strange running problems.

-1
Ð Awarded
Disagree
Rusty Owner/Technician
Massachusetts
Rusty
 

It stalls at IDLE and has adequate fuel pressure. Have you EVER had a FI vehicle stalling at idle that had a fuel supply issue? 🙄

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Rusty, Yes, I have, when a fuel pump would pass a pressure test but have low volume. This is shaping up to be a transition issue from base idle to initial acceleration though. I would be curious what the scanner readings are showing in live data. IAC. IAT, ECT and TPS. Measured at cold start and then after warmup.

-1
Ð Awarded
Disagree
Timothy Owner/Technician
Wisconsin
Timothy
 

Get OFF the fuel pump bandwagon Glenn. It has nothing to do with the issue. If you read the thread, the vehicle does not have ANY issue with fuel supply!!!!!!! Please refrain from passing off this advice as valid for the complaint!!!

+2
Ð Awarded
Agree
Interesting
Thanks
Rusty Owner/Technician
Massachusetts
Rusty
 

I think that YOU think you are a better diagnostic guy than you really are. I‘ve seen you send guys far away from the target in diagnostic direction and this “fuel filter” is a great example. Please stop posting junk advice that just wastes the time of the poster. You’re bringing down the value of this resource. Regards,

+1
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

A fuel filter will NEVER cause this set of symptoms! He states that the truck will run down the road just fine. That would be a supply side issue if it had that going on off idle, and he'd have lean codes, which has already been discussed. You may want to read the whole thread before jumping in with invalid suggestions.

+1
Ð Awarded
Agree
Paul Technician
Minnesota
Paul
   

Filter changed. Hooked up fuel pressure adapter in place of fuel filter &opened the valve to sample fuel. Engine did not stall or even change RPM's.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Exactly why this is not a fuel supply issue. The pump can supply quite enough pressure despite feeding the supply to the engine, and the ‘extra’ you're releasing into the sample container.

0
Ð Awarded
Robert Technician
Michigan
Robert
 

Are the valves lashed correct

-1
Ð Awarded
Disagree
Timothy Owner/Technician
Wisconsin
Timothy
 

That is actually not a bad thing to check.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

I should have mentioned that this is a Goodwrench engine with around 30k on it.

0
Ð Awarded
Curtis Mechanic
Florida
Curtis
 

Hey Paul check fuel pump ground on frame forward of left rear wheel for corrosion, butt connectors, or looseness, from previous repairs

0
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

Would that cause a stall at idle only in gear ? He has no extended crank. No lean codes.

0
Ð Awarded
Curtis Mechanic
Florida
Curtis
 

It's an intermittent. Ran into that problem a few times here at Fleet from hackers who are retired and gone now

0
Ð Awarded
Clint Technician
Illinois
Clint
   

Im going with the fuel pressure. The way I test these is by sqeezing the return line for a second with it running fuel pressure should go up. I like to see 13 psi without the return pinched and at least 20 or higher with it pinched. 10 psi or below will cause it to stall when you put it in gear.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

If it's fuel pressure, why does the truck do fine under load at cruising speed, and not run lean (trims are normal). You need far less fuel to run at idle than going down the road, so how would pressure have anything to do with that?

0
Ð Awarded
Clint Technician
Illinois
Clint
   

Its just they way these act. Been down this road many times when these trucks were the normal everyday vehicles that came in. Just like the 96-2000 wont start in the morning with 55 psi but start fine the rest of the day. No lean codes but the fuel pump is junk. No return pressure. Pump is running 100% and can't keep up.

0
Ð Awarded
Clint Technician
Illinois
Clint
 

If they don't have 12-13 psi. They stall when you put them in gear. Fuel pressure needs to be perfect.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Hate to call you on this, but I worked on these when they were new at the dealer, and have done ever since. What you describe is not valid nor possible to have a supply issue if the pressure does not fall under load. It is a law of hydraulics. I've had these run lean at the bottom of the spec., but never in the middle with no fall off under load. There is nothing wrong with the pump.

0
Ð Awarded
Clint Technician
Illinois
Clint
 

So you don't think he should test it? He should still test it. Squeezing the return line with a pair of pliers when its running will give him the info he needs. I didnt say load the parts cannon at it. I said test it.

0
Ð Awarded
Scott Owner
California
Scott
 

Hi Clint, Specs are 9 - 13 PSI. If this maintains at least 9 PSI under all conditions this is not a problem and it's not THE problem Paul is trying to fix. I've seen these start and run with as little as 3 - 4 PSI. Yeah, there's a drastic loss of power - and even though it takes forever and an eternity to turn on the MIL for DTC 44 stalling at an idle is not the complaint.

+1
Ð Awarded
Clint Technician
Illinois
Clint
 

Stalling at idle is usually always the complaint for me and I can never get a TBI to run right with less than 12. Especially on the Crossfire engine. I can't even count how many of those I fixed that were messed way up from people just screwing them up insead of fixing the fuel issue.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Since I worked at Chevrolet when the Crossfire injected Corvettes were new, fuel was almost never the issue with poor idles on those, but the balance of the injectors and breathing issues with the engine were the issue. It was a very poor design hence its use for just a couple of years. Clint, if you want to argue against the laws of hydraulics, you certainly can, but you've got no proof that…

0
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

Testing fuel supply/volume on an idle stall is a total waste of time. Suggesting such is an indication of poor diagnostic logic.

0
Ð Awarded
Clint Technician
Illinois
Clint
 

Lol. Im out. Have fun wasting your time with this one.

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
 

Indeed, Rusty. If it were me, giving the engine a mild shot of propane while it's idling rough would indicate if it's a lean problem, then I would move on…

+3
Ð Awarded
Agree
Paul Technician
Minnesota
Paul
 

Will definitely try that tomorrow or also hook up the Motorvac in place of fuel pump. Gotta find something on this one eventually.

0
Ð Awarded
Clint Technician
Illinois
Clint
 

I always squeeze the return line at the rear of the trans. If your pressure doesnt raise when you squeeze it thats a problem. Its worth it to test.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Definitely try that tomorrow.

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
 

Paul, I've read most of the replies and Rusty S. seems to be the only guy in the ballpark. Not saying this is your problem, but I've had injector drivers intermittently fail on these old TBI systems. Forget the lab scope. The quickest way to detect an intermittently failing injector driver on TBI is to connect a timing light (strobe light to the younger generation) and visually check the spray…

0
Ð Awarded
Thomas Diagnostician
Florida
Thomas
 

I had an old Cavalier that would intermittently stall. Caught the BARO pid flaking out when it acted up. That one an ECM took care of. Sadly not this one, but maybe look at the BARO pid.

0
Ð Awarded
Scott Owner
California
Scott
 

Hi Paul, I think Ken Palmer might be on the right track. Disconnect the EST connector, set timing to TDC. Leave it disconnected and drive it around. Is it still stalling at an idle? If it isn't - I'm not sure what is available for distributors on this anymore, but that usually was the magnetic field on the main shaft had a cracked magnet and the signal for the P/U coil was not strong enough to…

+1
Ð Awarded
Cliff Diagnostician
California
Cliff
 

I would lean towards a distributor issue on this as well. I would think that scoping the injectors as well as the ignition pickup and the signal to coil would be what I would do. I think something is “spiking” the computer and causing it to shut down. Just remember NEW=Never Ever Worked.

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Paul, Check out TSB# 41-65-22 dated Sept. 1994 for revised idle speed specifications. Another thing to consider is if this engine has high mileage, a minor adjustment of base idle may be required. The new TBI unit you have is not factory new, it is an aftermarket reconditioned unit. The other issue to be considered is the lock up convertor having possible issues. If you locate the…

-1
Ð Awarded
Randall Technician
Pennsylvania
Randall
 

Paul, I would be thinking about scoping the ignition and injectors. Is it losing timing control? Injector on time? Ignition coil dwell? Etc. Don‘t ya’all miss the 80’s and 90’s vehicle “no code drivability“ days? Randy

0
Ð Awarded
Mark Engineer
Colorado
Mark
 

Paul You mentioned: “stalling in gear at low rpm. ” There has been great advice in this thread. So that we can offer pinpoint direction, is it your opinion that the stall is a result of the low RPM (which you mention happens after the transmission is put in gear)? Others in this thread have mentioned the transmission causing the engine to stall. Another piece of diagnostics offered was to…

0
Ð Awarded
Tom Owner/Technician
Tennessee
Tom
 

Maybe it has been asked, but what are the IAC counts? Although these have the ability to compensate by adding IAC counts if necessary, many of them were “unhappy” if they were outside of their "normal" expected window of operation. In my experience, IAC counts should be 8-15 fully warmed at idle with no load in park or neutral. Maybe your “new” unit was not/is not set correctly. I still have…

0
Ð Awarded
Darren Owner/Technician
Arkansas
Darren
 

Hello Tom, I just broke this out about a year ago for an IAC problem on a 2.5 S10, first time since 2004. Handy bugger for those difficult to set idle air controlled vehicles when driving is not an option.

+1
Ð Awarded
Robert Technician
Michigan
Robert
 

So it actually does have a $25 set of plug wires on it ?

0
Ð Awarded
Rusty Owner/Technician
Massachusetts
Rusty
 

Failing plug wires will cause a miss when wet or under load. Not at idle.

-1
Ð Awarded
Matthew Diagnostician
Kentucky
Matthew
 

can U keep the engine from stalling by tapping the throttle.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Yes. If you do a “mild power brake” as you are moving slowly it will not stall.

0
Ð Awarded
William Owner/Technician
Kentucky
William
 

Have you tried unplugging the egr valve? You said fuel trims are good, but a over active egr valve will cause a hesitation and stall without setting any codes. With the vehicle idling if you snap the throttle does the valve open up all of the way, it should just open, not all of the way open.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

We tried that, installed an EGR block off plate to no avail. This one is really eating our lunch.

0
Ð Awarded
William Owner/Technician
Kentucky
William
 

If I remember correctly there were two styles of fuel injectors used a normal one and peak to peak injectors. A peak to peak injector would open with 4 amps draw and would stay open with 1 amp, there were cases of extreme ring voltage, you can observe with a lab scope. Sometimes putting a capacitor in parallel with the injector would cure a hesitation caused by this voltage. I think it was .1…

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Paul, The distributor was replaced and the coil. Have you looked at the coil lead carefully for “green corrosion”? You said grounds were cleaned. These had issues with the ring terminals on the grounds at the thermostat and the rear engine block to fire wall ground. Also consider engine harness is being torqued when it is put in gear, so perform a wiggle test on the engine harness…

0
Ð Awarded
Bradley Educator
Ohio
Bradley
 

Here's one more shot in the dark, but have you verified the braided ground in the back of the passenger cylinder head? I had a TBI C1500 20 years ago that stalled after 20 minutes of driving, but would idle for hours with no problem. We chased fuel supply, fuel delivery, ignition, everything for days. It had been to three shops before my students started looking it over and had had a thousand…

0
Ð Awarded
Mark Engineer
Colorado
Mark
 

Bradley it looked like independence day between the engine and firewall. That braided ground was corroded through Good find (back in the day). I keep one on hand because they are that important. The NAPA number is 770-6119 and it is real important for it to be braided, and not a wire with lugs on the ends (a whole other discussion for another day on why it has to be braided).

0
Ð Awarded
Matthew Diagnostician
Kentucky
Matthew
 

braided is for absorbing rfi I believe

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Mathew: Here is some helpful information: Ground Strap Braid Basics for Electrical Protection (falconerelectronics​.​com)

0
Ð Awarded
Matthew Diagnostician
Kentucky
Matthew
 

appreciate it.

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hello Paul, Have you been keeping written note as you go or are you trying to memorize everything? My advice would be is to write everything down and build a game plan of what direction this is going. Go back through all the replies so far and make yourself a history file. There are times when this effort pays off because the problem will likely jump off the page at you. What is absolutely…

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

Did pre OBD2 GM cars show "Load" in the data list? Maybe the torque converter is going bad.

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
 

Hi Geoff, I recall “Block Learn” was the common computer strategy back then. Block Learn Multiplier and Integrator (gnttype​.​org)

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

which has absolutely nothing to do with what I asked.

+2
Ð Awarded
Agree
Gary Owner/Technician
Colorado
Gary
   

Hello, Geoff. I don't recall any OBD I GM software having a load PID. About 15 years ago, I had intermittent stalling problems on some old OBDI TBI Chevy pickups and vans. The data update on a scan tool is too slow to capture a momentary loss of fuel or ignition. The first case really gave me fits because I couldn't always duplicate the problem or get a valid injection capture on a my lab…

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

Thanks Gary. The only one of "these" I saw, I actually DID diagnose with the scan tool. Sort of. The iATN archives had people saying distributor magnets got weak, and/so I graphed the RPM (using my Mastertech as a Tech1A). The RPM would go steadily down to about 800 or 750 and then drop straight to zero. New distributor fixed it.

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
   

The RPM would go steadily down to about 800 or 750 and then drop straight to zero. New distributor fixed it. Indeed, Geoff. Two-wire magnetic reluctor sensors are very speed sensitive. Weak sine wave signals from these types of sensors can definitely cause stalling complaints under the right circumstances. If I recall, a few the old 350 TBI distributor shafts actually became magnetized would…

+1
Ð Awarded
Agree
Helpful
Interesting
Thanks
Timothy Owner/Technician
Wisconsin
Timothy
 

Agreed Gary. I have had way too many times where the scope shots were perfect, yet the codes would set. Constant PITA on the Chryco CKPs for years. Often was cheaper to replace than test. And, in many cases, the replacement, if not OEM, was suspect on a repeat fail… Did a 93 K1500 just a few days ago, and the pickup in the distributor had failed. Easy-peasy, right? Noooo! Tried three AM…

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
 

I have had way too many times where the scope shots were perfect, yet the codes would set. Constant PITA on the Chryco CKPs for years. Often was cheaper to replace than test. Right on, Timothy. I'm not against using scopes, but the systems they test can be really diffcult to diagnose. To illustrate, I recall an old OBD I EEC-IV Ford with an intermittent stall. I scoped the PIP and SPOUT…

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Indeed. I remember when I could ascertain what was causing a misfire without using a scope ever. Now, misifre diagnosis is one of the biggest PITA that occurs, what with engine designs not allowing access, or very limited access to cylinders. And the paddle type of pick-up, (even my vaunted Pico paddle), sometimes gives me useless scope shots that are questionable integrity at best…and, without…

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
   

Back when I started in the gas station in 1957, many engines didn't use spark plug boots. So the mechanic would short each of the spark plugs with his finger to find the dead cylinder. The trick to not getting shocked was to not complete the circuit by touching the engine or leaning on the fender. Back in that day, we had either a fouled spark plug or a burned valve or (on the flat head…

0
Ð Awarded
Glenn Owner/Technician
Texas
Glenn
   

Hi Geoff, That would mean no there is not a PID for load and the calculations had to be done manually.

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Finally got back on this one. In scoping the injectors noticed when it fluttered or stumbled, injectors were being “double fired” 3.8 ms apart at idle. Very intermittent but double fires exactly when engine stumbles. Any thoughts. Reman ECM did not change this. Thinking defective reman distributor/module[?]

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
 

Hello, Paul. I had a 1983 Jeep CJ that would intermittently go rich at idle. It had the Howell fuel injection conversion, which was essentially an old GM minimum function system converted to replace carburetors. Long story short, I used my old BDM OBDI scan tool to diagnose the problem because it didn't require a VIN to identify a vehicle model. Turned out that the idle speed on the data stream…

0
Ð Awarded
Paul Technician
Minnesota
Paul
 

Thanks for the input. The 2 distributors that have been tried are AM units. Am going to pull the trigger on AC Delco distributor. What a long journey on this one.

0
Ð Awarded
Scott Owner
California
Scott
 

Paul, I'm sure it got lost in all the posts, but if you open the EST connector (the one for checking timing) does the engine still stall at an idle? Good luck finding an actual AC Delco distributor as these are remanufactured by?? Years ago when GM had discontinued the distributors and any of the parts to rebuild them, there were new distributors available from GM Performance, part # 1103952…

+1
Ð Awarded
Agree
Paul Technician
Minnesota
Paul
 

Totally agree. Going to try one more distributor from a different supplier, & if that doesn't work I am just going to cut my losses & wash my hands of this one. Will know tomorrow.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

As the vehicle builds get better and better, and last far longer than anything from years past, (especially in the corrosion states) this will indeed become an issue that has no resolution.

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
 

Hello, Paul. I was over two months on this Jeep because it was an intermittent condition. Fortunately, the guy was working 12 hrs/day at our local prison due to the COVID epidemic, so I had plenty of time. But two CKPs per cycle = double the fuel on this problem. I used an industrial scope on coil minus to find this problem. A regular lab scope requires an attenuated lead to monitor primary…

0
Ð Awarded
Randall Technician
Pennsylvania
Randall
 

Paul, The guys on this network enjoy scope patterns. If you could post a distributor reference and injector driver trace, I believe that it would be appreciated. I have seen unusual injector firings long ago when a system was in a “stall prevention“ idle strategy. Not sure what brand at the moment. Is it possible that the torque converter is to blame? I had a similar issue in an 3.8 with a…

0
Ð Awarded