1990 Bronco electrical ghost?

Roberto Owner/Technician Fremont, California Posted   Latest   Edited  
Discussion
ATS - Automotive Test Solutions
Driveability
Electrical
1990 Ford Bronco Custom 5.8L (H) 4-spd (AOD)
Rough Idle

This vehicle has a very bad idle condition, someone has replace a lot of things before I got the truck, the PCM, MAP, TPS, ECT, Air temperature sensor, and loose track of the parts, but the funny thing that I was able to see so far was that when I disconnect the TPS or the MAP sensor the RPM stables, only that when I disconnect the MAP sensor the Pulse with increases too, but when I disconnect the TPS the pulse with stays about the same with smooth running condition, but the funny this is the picture Am posting, where the waveform looks smooth, is when I disconnect either the MAP or TPS, and when the waveform looks noisy truck is idling bad, what you guys think?

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Rudy Technician
Montebello, California
Rudy Default
 

Im pretty sure you can see the fuel trim on this truck. Do you have a scanner capable of connecting? Any codes?(I dont have an answer for your scope question,Im not so sure it is related,but Im not versed enough in that matter to answer correctly.)

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Rudy: No scan tool serial data on this vehicle that far back. Guido

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

I believe 1992 was when the data came in. However, if there are 5 wires in the data connector, you can lie to the scan tool and enter a later year, data will appear. If it has 4 wires, no data!

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Jamey: I thought that it was 1994. Guido

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

1994 Is when Ford advertised it as a data stream, but as early as 1992 the connector had 5 wires in it. The 5th wire is the data stream. I would tell my old red brick that I was connecting to a 1994, but read data on a 1992 :-)

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

I guess that I should've held onto that l'il grey cell. Oh well. I'm sure that I had fun losing it. Thanks for the correction, Jamey. Guido

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

Haha! You’ve probably forgot more than I know 🤓

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Randy Diagnostician
Glendora, California
Randy Default
 

Nothing like old timers . No scan tools with pids . Were do you go??. Gut filling

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

I've never seen data on any pre-OBD2 Ford. And we have a bunch still here. I wonder if it's on CA emissions only.

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

I bet most of the Ford’s you see have California emissions. But I don’t think it was California only. Connect to one with your red brick and see, or any other old school scan tool that is pre OBD II. If the dog house connector has 5 wires, it has a data stream.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

You would lose that bet. I'm the only one in the shop that writes that down, and I do it on every car I look at. Most of the cars here came here with somebody and got left when they decided not to stay. Almost nobody moves here from Cali. Oregon and Washington are tied for #1. Pretty much any random place else after that. I'll try and remember that fifth wire tip, thanks. Probably be a month…

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Dominick Technician
Bernardsville, New Jersey
Dominick Default
 

Pretty cool problem. First thing would be to check the electrical system, bat. Alt.. i would think with the sensors plugged in its causing one or more of those circuits to be pulled down which is affecting the injector or pcm injector control circuit. look at a wiring diagram see whats what. Ck the 5v ref supply and grounds to the TPS and map plugged and unplugged.

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Karl Owner/Technician
Reading, Pennsylvania
Karl Default
 

Did you measure how much AC voltage is present?

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

You can try adding a ground to the PCM, but that fuzzy signal is usually an internal PCM ground issue. It's not as bad as some, but I have seen that signal before. You will most likely see the fuzz on all your PCM out puts and signals. Here is an injector circuit that I had. This fuzzy signal was on all my outputs.

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Oscar Technician
Santa Barbara, California
Oscar Default
 

Had a similar issue, chased my tail a bit, sent in the PCM to get checked out by a rebuilder, they stated that it was OK, chased my tail some more circling around the PCM, ended up replacing the PCM and took care the issues.

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Albert Owner/Technician
Towanda, Pennsylvania
Albert Default
 

I don't much about wave forms I'd like to see what more experienced reform guys think. I'm guessing but I would say bad ground?

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Rob Owner/Technician
Nanaimo, British Columbia
Rob Default
   

Check the main ground wire that has a connection by the rad support​. Quite often it is damaged or not hooked up after battery cable repair. Check the AC ripple at the alternator and not at the battery under load​. ​If equipped disconnect the DPFE sensor and see what happens,they would short out and short the reference voltage to ground..

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

Where is your scope grounded, and is the ground a good clean ground? Have you scoped the voltage ripple from the generator? What is the koeo frequency of the MAP sensor?

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Gail Technician
Garner, North Carolina
Gail Default
 

Albin is referring to HZ reading of MAP sensor. I agree. Seen them get skewed enough to cause drive-ability concerns but not set a code. Plus this system was just about the most "stupid" of this eras vehicles. EEC systems were tough to diag. They did not output data until around 1994 i believe?

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Randy Diagnostician
Glendora, California
Randy Default
 

Gail thats is why we used brake out boxes to diag on the early ones

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Chris Technical Support Specialist
Commack, New York
Chris Default
   

or SBDS pbs​.​twimg​.​com/media/CIxn8R7U…

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Randy Diagnostician
Glendora, California
Randy Default
 

Chris do you remember snap on simu-tech. What a great tool

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

I was a dealer guy for most of my career. SBDS was a necessary evil. Too many cables, computer problems, finicky touchscreen, but the only way to do it.

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Gail Technician
Garner, North Carolina
Gail Default
 

I wasn't in Ford dealership back then. And back then when i was looking for a break-out box other people thought it was a waste of money. Just keep replacing parts until it's fixed was their motto. I still think they sucked.

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Roberto Owner/Technician
Fremont, California
Roberto Default
 

Wonderful guys, I’ll answer some of the questions you guys have after doing more testing, definitely leaning towards a ground issue or PCM.

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Randy Diagnostician
Glendora, California
Randy Default
 

i was not at dealer either . but i used BOB all the time

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Gail Technician
Garner, North Carolina
Gail Default
 

During the 80's & early 90's i lived in WV. They barely had running water. Forget about buying diagnostic tools. I bought my own Rotunda BOB after i moved to NC in 1996. Much too late.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Back-probes weren't invented yet?

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Gail Technician
Garner, North Carolina
Gail Default
 

Nope. Used paper clips. But reading data on GM & Mopar for years before Ford spoiled me.

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Randy Diagnostician
Glendora, California
Randy Default
 

Butt hat pins were . And some guys still use them

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Gail Technician
Garner, North Carolina
Gail Default
 

Butt Hat? That a fashion choice?

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Randy Diagnostician
Glendora, California
Randy Default
 

Other wise known as t pins . Scaner danner still uses them and sma auto . I donot like them to big

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Gail Technician
Garner, North Carolina
Gail Default
 

Was just making a joke out of Butt typo.

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Randy Diagnostician
Glendora, California
Randy Default
 

lol

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Roberto: I'd be curious what you get for a reference voltage reading (voltage and quality) and sensor ground at the MAP & TPS. If good, I'm inclined to go along with the others on excessive A/C ripple from the alternator or a bad ground. If your VREF is low or noisy, I'd look at a schematic to see what else is shared on the VREF circuit branch/s. Note: there should be more than 1 VREF…

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Mike Technician
Atlanta, Georgia
Mike Default
 

Roberto, I'm having some issues with the site so images won't display full size, but I can see the thumbnail well enough when I right click to a new tab that the pulsing you are seeing is pretty regular. Start scoping other components to see if it is on them as well.

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Stephen Technician
Gallatin, Tennessee
Stephen Default
 

The 2 photos indicate that the noise is on the 12v supply but isn’t actually affecting injector operation. Since unplugging sensors cause the noise to cease, I would look at the source and grounds for the sensors. The patern of the noise doesn’t look like typical alternator noise but the voltage regulator might be suspect. This one is much older but odd noise on the sensor supply caused by the…

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Roberto Owner/Technician
Fremont, California
Roberto Default
 

Guys, one of the things I forgot to ask was if on this fuel injection sistem, is normal for the computer to turn all the injectors at the same time? Because this truck has two banks one ground for 1-4-5-8 and another ground for 2-3-6-7, is it normal for the computer to open the injectors at the same time, even having two banks? I try to find this information in alldata, mitchell but is no…

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Roberto: What is on the VECI label? Guido

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Roberto Owner/Technician
Fremont, California
Roberto Default
 

Here is the label

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Gail Technician
Garner, North Carolina
Gail Default
   

NOT SFI but being California emissions I'm not sure what they did. At lower right says MPI. Batch injection.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Gail: And the top says EEC-IV. They're bank fired. Guido

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Maynard Technician
Elmira, Ontario
Maynard Default
 

Hi Roberto I will just throw this out there, its more of a silver bullet thing than a test and arrive at a solution. The silver bullet part is, "try adjusting up the minimum airflow idle stop, count the number of turns in case you want to put it back because it doesnt help anything or whatever. Of this vintage I have seen a couple times that adjusting that up seems to clear up some idle…

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Roberto Owner/Technician
Fremont, California
Roberto Default
 

Ok guys, after installing the original module on this truck this is what happened, the ground signal went back to normal, that means the ground issue was from the computer, the grounds going to module are ok with a minimum noise, customer installed a reman module that had some problems and he assumed that the problem was somewhere else, so he kept replacing parts until he gave up, installing the…

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

CIP-Customer Induced Problem!! Glad you got it !

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Albert Owner/Technician
Towanda, Pennsylvania
Albert Default
 

Don't you just love it when people just throw parts at a symptom and not even try to find the problem. I'm sure the customer is glad you stayed the course.

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Jesse Owner
Roanoke, Virginia
Jesse Default
 

Sooo many problems with modules. And difficult to get a good one.

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