No injector pulse

Doug Owner/Technician California Posted   Latest  
Updated
Driveability
2000 GMC Jimmy SLE 4.3L (W L35) 4-spd (4L60-E)
Crack No Start

Greetings technicians. So on this GMC Jimmy crank no start, it has good fuel pressure and when I introduce some brake cleaner it will fire. I have scoped the injectors and I get power but no injector pulses. As the picture shows they're being pulled to ground but I show no Pulse signals as expected.

I'm wondering if this is because the injector module has failed. I have another one and I'm about to change it but would like to get some pointers from somebody that might know. Thank you, Doug

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Boyd Technical Support Specialist
Georgia
Boyd
 

Doug the injectors are controlled by the PCM based on the fuel control signal from the ignition module. Are you sure you don't have an open circuit TPS causing a clear flood condition.

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Doug Owner/Technician
California
Doug
   

No Boyd, not necessarily. There are no codes but I will check the TPS signal. Has a good Cam and crank signal. Possibly might also be a bad ignition module?

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Jürgen Owner
Mexico
Jürgen
 

+1, though “typically” the engine keeps running after startiing it with brake cleaner. The op doesn't tell wether this is the case or not.

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Andre Diagnostician
District of Columbia
Andre
 

That may be true on a lean condition but with no injector pulse you have no fuel and therefore it will not continue to run

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Jürgen Owner
Mexico
Jürgen
   

There are applications where clear flood will be cancelled once the rpm raise above a defined threshold. The injectors then will be pulsed normally until the engine is shut off and the no start scenario will repeat. The above mentioned is applies to drive by cable systems.

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Doug Owner/Technician
California
Doug
 

Yes, what was odd during cranking it wasn't showing any RPM signal. I checked cranks in the grill and it was good and after I sprayed in some brake cleaner it ignited for a couple seconds then quit. The RPM signal did jump up when I did that.

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Richard Technician
New York
Richard
 

there is no high voltage spike. Maybe a power feed issue?

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Eric Owner/Technician
Michigan
Eric
 

Yes, there isn't any inductive kick. Can't see your voltage level. Do you have a current probe?

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Doug Owner/Technician
California
Doug
 

It's at 12 volts battery voltage. And yes I do have a current probe. Put that on one of the injector wires and see what current it's pulling?

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Doug Owner/Technician
California
Doug
 

Thank you, check the power feed and it is battery positive.

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Michael Mobile Technician
Utah
Michael
 

Doug, It is hard to tell what the settings are on your scope, but there is definitely a problem. There seems to be hardly any on time. Can you show us how you have the scope grounded and connected to injector? Depending on how it is connected, the waveform could be different.

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Doug Owner/Technician
California
Doug
 

Yes thank you Michael. I have ground to engine ground and the other scope wire plugged in to one injector wire. And yes there is no Spike, it's just pulling it to ground.

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Ray Diagnostician
Ontario
Ray
   

Doug, 2000 Safari 4.3, known good In the first capture, the blue channel is the ckp sensor voltage with the engine cranking to start. The red channel is the cmp sensor voltage The green channel is the coil wire secondary The black channel is the cyl 1 plug wire, sync The second capture is the ECM B fuse, the ign coil and the injector amps

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Thanks
Allan Instructor
Manitoba
Allan
   

Your battery voltage looks very erratic, have you load tested the supply circuit to the injectors? You have no inductive kick from the injector. If you have little or no current available for the injectors the coils won’t be charged and there won’t be any inductive kick. What is the voltage scale on your scope? How much does the voltage actually fluctuate? Checking current at the injectors with…

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Thanks
Doug Owner/Technician
California
Doug
   

Yeah sorry for the poor scope picture. It was set at 20 volts. I will be doing the amperage test as Ray has shown on the ECM 1 Fuse.

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John Mechanic
Tennessee
John
 

I have seen many of these connections at the crank sensors become saturated with oil and do a bunch of crazy stuff make sure your connections are oil free and wires feel solid

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Jon Owner/Technician
California
Jon
 

Your erratic looking voltage is normal for the snap-on brand scopes. They tend to pick up the ignition noise easily. (unshielded cables) You can ignore it or move your leads around a little to clean it up. I seem to remember a switch in the distributor that had to close to signal the computer it was in crank - I could be wrong. I think it is labeled as a cam sensor on wiring diagrams so its a…

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Dan Owner/Technician
Texas
Dan
 

… In the act of “pulling to ground” they should SQUIRT and deliver fuel to the POPPIT… sounds like they are glued SHUT… I would install an upgraded MFI (true PORT injection) unit , whereas the injector is relocated from the fuel charging BODY to where the poppit USED to live… this was done in in later models from the factory… poppit systems are very problematic. Dan H. … Hobbs.

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Darren Owner/Technician
Arkansas
Darren
 

What was your fuel pressure? Does it hold pressure after key off? Has it been converted to MFI (each injector has 2 wires following the feed line)

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Doug Owner/Technician
California
Doug
 

It's 60 lb and yes it holds pressure. No I haven't changed it yet but I have one to do. I don't know but I'm thinking that the driver inside the computer might be bad. Thanks Darren!

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Michael Mobile Technician
Utah
Michael
 

Doug, Just thinking out loud here. I have seen one or maybe two drivers go sideways at about the same time but not 6 at a time in the same way. The issue is affecting 6 injectors. This would lead one to believe that the issue is with a source either power or ground that the injectors share in common. It could be inside the PCM yes, but more likely somewhere else. It could be as simple as a bad…

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Doug Owner/Technician
California
Doug
 

Thank you Michael! it was connected. Both the power and the ground were okay. And the battery was sufficiently charged. And I only checked one injector. Before when it started I thought it was out of gas, put gas in it and ran for a couple of blocks but then quit. And couldn't get it to go anymore. Previously it's had a battery drain issue of which I haven't located. The driver did say that the…

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Richard Technician
New York
Richard
 

If your up to it I have used a incandescent test light to manually fire the injectors and see if they will indeed open

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Doug Owner/Technician
California
Doug
   

So I grounded it with my test line and it only pulled it to down to 8 volts with no inductive kick. Of course that's not enough grounding to do that. I should just do a jumper wire without the test light? And I haven't had a chance to hook up an amp clamp yet. Had to get it towed and I'll get back to it a little later.

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Dan Owner/Technician
Texas
Dan
 

… You need to do your injector activation with a “Buzz Box”… a firing device… you do this directly on the pins in the TOWER … with the gang connector removed. … Dan H. … Hobbs … South Texas …

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Doug Owner/Technician
California
Doug
 

Don't have one Dan but I do have an injector activation tool. I can do the leak down test and see if they are opening? That does work on these type of injectors correct? Or maybe not?

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Dan Owner/Technician
Texas
Dan
 

… That is what a buzz box IS… and YES …that will work… Dan H. … Hobbs … again …

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Doug Owner/Technician
California
Doug
   

Oh my God, duh lol. what a dits… sometimes! How can I delete that previous post. :-D

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Dan Owner/Technician
Texas
Dan
   

… Here is a picture of me “buzzing” a SCFI injector members​.​iatn​.​net/file/view/?id… note the spray from the breached tube (above the “5” )… that system HELD rest pressure 100% (other than the slow drip from the regulator…that is what provided the fuel for the “internal FIRE ” that was inside the upper plenum)… as the breach was down wind of the injector. … Dan H. …

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Richard Technician
New York
Richard
 

yeah i am not sure about the older style injectors on this but i have done it on newer systems no problem. I assume the older ones were less efficient and thus require more than current than available with the added resistance

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Doug Owner/Technician
California
Doug Update
 

Well but it's testing the old injectors on it didn't do anything to the fuel pressure. Installed the new spider injection that I had then I was able to get them to squirt! Still won't start. I'm going to scope the injectors again and if I don't get any spike I need a new computer.! Definitely not activating the injectors because I can get it to run with alternative fuel.

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Dan Owner/Technician
Texas
Dan
   

… Does what it IS squirting now BURN (not WATER or DIESEL) ???… Spark verified on all cylinders AT the plug wire end with a ST-125 tester (this IS important) … CAP can be FUNKY…even a NEW CAP???… and IF it had compression(and an open exhaust) it SHOULD run … or at the least DO SOMETHING … fart … backfire … jerk … SOMETHING. … Dan H. … Hobbs.

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Doug Owner/Technician
California
Doug
 

Squirting carburetor cleaner gets it around for 2 seconds then Burns it out. Does not have any injector kick I ordered a new computer and will update after I get it. I appreciate your guys's input., Thanks for trying!

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Dan Owner/Technician
Texas
Dan
 

… Does ONE of the wires going to each injector get hot when the key is turned ON ??? It should. … Hobbs …

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Dan Owner/Technician
Texas
Dan
 

… Wait…you said they squirted after spider replacement… therefore there was pulse (at that time)… must be squirting something that will not burn… that's the way I have it figured… it LIKES SPRAY …but doesn't LIKE what it is capable of delivering out the (relocated) injectors… right ? … Hobbs.

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John Mechanic
Tennessee
John
 

Maybe put a little oil or Trans fluid in your cylinders a bunch of cranking can wash your cylinders down just don't overlook compression

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