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Discussion Starter · #1 ·
Hey everyone,

So, I bought a 91 Trooper over a month ago. It has a brand new Jasper 2.8L V6 motor in it. The issue I'm having and the previous owner had, as well, is that on cold starts it cranks right up but wants to stall out unless you feather the gas pedal until it is somewhat warm, no more than a few minutes, then it idles fine. Then, once the engine is warm, say near or at running temp, and you turn it off then go to start it again while still warm it will flood out. To avoid flooding it i have to clear flood start it (hold it to the floor). Then the idle will sometimes surge up and down for a few minutes then idle normal, purring like a cat. Every now and then it will surge at running temp when sitting at idle at a red light or stop sign, but it's completely random. No rhyme or reason. When driving, there's no noticeable misses or surges, operates great. I can smell fuel fumes around the engine bay and my milage is suffering so i believe it's definitely running rich.

Things ive replaced in efforts to solve the issue:

Coolant temp sensor (the one that communicates with ECM) located on top near intake
MAP Sensor
Idle Air Control Valve

TPS (was put on in April by previous owner, it's showing 3.5-4 volts when throttle full open so it checks out)
EGR valve isnt brand new but it's not the original either and it still holds vacuum.
Throttle Body is brand new, injectors are new and spray good, pulsating cone.

I've also checked for vacuum leaks with carb cleaner to no avail, any help would be GREATLY appreciated as I'm not far from going mad.

Thanks in advance!!!!
DLA
 

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Start by replace the igniter. This part has always been a problem for GM engines of this era. When you do thoroughly inspect all the electrical contacts and you must apply the heat sink compound to the mounting surface. Next unplug your coolant temperature sensor when cold. drive the vehicle and pay attention for any noticeable difference in performance. If the engine runs better replace that too.
 

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Discussion Starter · #3 ·
I have some additional info, i just ran the diagnostics using the spade connector and female connector in the center console, (just read about it online, otherwise i would've done this from the jump). Im showing code 54, anyone know what that could be?
 

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Just noticed, as well, the EGR Solenoid has 4 pins, my EGR solenoid connector only has 3 pin slots, 1 is missing. Only has 3 wires running to it, as well. Is that correct or should there be a 4th pin slot and wire?
 

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Did you figure out the issue? If not, look for a air intake leak around base of throttle body by spraying some engine start spay at the base looking for RPM surge. There are 3 vacuum hoses behind behind the throttle body and a flapper valve in the air intake hose vacuum activated with a sensor in the air filter housing … check as well. also try swapping the MAP sensor, it’s easy done as it’s mounted on outside of airfilter box. Hope this helps.
 

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According to the above, Code 54 is "fuel pump voltage low". So there might be a problem with a relay, the connection near the passenger's rear wheel well, or the fuel pump itself.

One other thing on the GM Rochester 220 TBI-EFI system, anytime you make changes to the tuning or replace a sensor, you'll typically need to readjust the minimum idle speed and check/adjust TPS voltage.

Otherwise the engine will be quite cranky, as you've described.

Here's a good site for testing/troubleshooting, and below that I'll paste in the instructions for setting the minimum idle speed and TPS voltage. HTH...............ed


<Hat Tip to the author of this article, Jay Vessels>

Adjust your TPS and I.A.C. on your TBI / MPFI
Authored by: Jay Vessels


Tools needed:

Torx bits or drivers (T-10, T-15, maybe more depending on the application)
Voltmeter (digital is best, but a really accurate analog will work)
Tachometer (the one in the vehicle will work fine if equipped)
Wrenches and an awl (various sizes, only if the idle speed hasn’t ever been set)


Theory of Operation – (lengthy)

A common myth about fuel injected vehicles is that the idle speed is fixed and cannot be adjusted. This isn’t quite true; there is a setting. It's called minimum air, which is adjustable on TBI and MPFI vehicles. This setting sets the lowest-possible idle speed for the vehicle. The ECM uses the IAC (idle air controller) to raise the idle speed from this adjustment. So, while the exact idle speed isn’t really adjustable, the minimum idle speed is.

Why adjust the idle speed? Isn’t the ECM supposed to do that? Yes it does and it does do a good job, but has to have a starting point. That starting point is called minimum air, or the smallest amount of air allowed to enter the engine with the throttle closed. The ECM can only add air to that minimum setting. If that setting is too high, the ECM can’t slow the engine down to an acceptable idle. If the setting is too low, the ECM may not be able to keep the engine running under certain conditions.

Another reason to adjust minimum air is if there has been some repairs to the fuel system. If the throttle body has been removed (i.e. rebuilt or cleaned) or the TPS (throttle position sensor) has been replaced or otherwise disturbed (i.e. loosened the mounting screws unintentionally -- it happens) then minimum air should be adjusted. Any changes that could affect idle speed or idle quality, like performance upgrades or replacing leaking vacuum lines, should be followed by setting minimum air.

This adjustment, once learned, only takes a few minutes. It rarely has to be adjusted, but it takes so little time to check (and adjust, if needed) that there’s no reason not to do so.



Checking & Adjustment Instructions

To establish minimum air, the idle speed must be set first. The idle speed screw is sealed with a cap from the
factory. This should be removed by removing the throttle body and using an awl to pry the plug off. If this seems scary, have it done. It’s not difficult but it’s not worth risking damage to the throttle body or human flesh to remove the plug. Once the plug has been removed, reinstall the throttle body.

Assuming the idle speed screw is accessible and the throttle body is installed, jumper
pins A&B on the ALDL (Assembly Line Data Link) connector under the dash. Pins
A&B are on the upper-right-hand side. These are the same two pins to jumper to
read codes from the ECM. Now turn the key on (the Check Engine light should be
lit) and leave the key on for at least 30 seconds. The computer will extend the IAC plunger all the way out to allow adjustment of the idle speed.

(Note that on a Trooper, the ALDL plug is in the center console, under the pullout tray.)

After the 30 second wait, unplug the IAC (square 4-pin connector on the throttle body) WHILE THE KEY IS STILL ON. This prevents the ECM from adjusting the idle speed while you make your adjustments.

Block the drive wheels, set the emergency brake, and start the engine. Set the idle speed by adjusting the idle
speed screw. The engine should be at operating temperature for this. The exact setting is on the emissions label on the radiator shroud, but in general, the idle speed should be about 500 RPM in Drive, 700 in Park / Neutral, or if you have a manual transmission, somewhere between 600-800 RPM. Remember that the truck is running during this adjustment, so stay clear of the fan, and make sure it can’t roll or otherwise be put into gear while this is done.

Once the minimum idle speed is set, turn the engine off, reconnect the IAC, and remove the jumper from the ALDL connector. The TPS minimum voltage must now be set. Turning the idle-speed screw may have moved the TPS idle voltage away from the specification, so it should be adjusted next.

Connect a voltmeter between pins A (usually dark blue) and B (usually black, or black/pink) of the TPS, and turn the key on. Don’t start the engine. Loosen the two torx screws holding the TPS in place, but don’t remove them. Rotate the TPS until the voltmeter reads between 0.45 and 0.55 volts, with 0.50 being ideal. Tighten the mounting screws (carefully, they thread into soft aluminum) and re-check the voltage to make sure it’s still within range.

That’s it. After the procedure is done once, it’s easy to remember and do. I hope this helps.
 

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Curious, Jasper told me today they do not stock the 2.8 liter v6.
Well, lots of things are going out of stock nowadays!

I've seen the 3.4 F-body V6 out of stock at Rockauto, Jegs, Summit Racing, and at a number of local stores such as O'reilly.
 

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Well, lots of things are going out of stock nowadays!

I've seen the 3.4 F-body V6 out of stock at Rockauto, Jegs, Summit Racing, and at a number of local stores such as O'reilly.
I'm currently waiting for a 3.4 from O'reillys. They are crazy backed up for it and I think they said i'm 7th in line for it. Almost tempted to pick and pull one.
 

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I'm STILL waiting for the slide door for a 2019 Ford Transit Connect. Been six months. Was SUPPOSED to be here day before yesterday. Now told the 30th (4th time for this kind of story). Dennis
 

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I'm STILL waiting for the slide door for a 2019 Ford Transit Connect. Been six months. Was SUPPOSED to be here day before yesterday. Now told the 30th (4th time for this kind of story). Dennis
Horrific breakdown of everything. Time to make sure the pantry is full. Actually past-time!
 
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