ok, so for those of you who read my "turning a 2.8L into a 3.1L" thread, you have the idea of what I did... for those that didn't... I had originally intended to swap the crank along with all the accessories from my 3.1L in my '92 RS that was having serious valvetrain issues, to an '85 2.8L motor... however one of the pistons ended up being trashed, and I do have pics up in that thread...

ok, so I installed the 2.8L a few days ago, have all the 3.1L accesories bolted up, I installed all the 3.1L sensors, the 3.1L injector rail and injectors, I capped off the cold start injector, installed the 3.1L plenum, swapped to brand new spark plugs I bought for my 3.1L with new wires, and new dist. cap, also replaced the ignition control module, even tried swaping the coil with a spare I have and I DO HAVE SPARK... also installed a new f/f which looks like it hadn't been changed in a decade

think a 2.8L block, heads, intake manifold (not plenum), distributor and starter, everything else is 3.1L

I've had to clean the spark plugs a few times now, but the engine is still running rediculously rich and keeps flooding and won't start

could it be the injectors? I read that the 3.1L injectors would work for the 2.8L... could it be the intake gasket not tightened down proper? that shouldn't cause the mixture to be so rich...

it's all the plugs, not just one that are fuel soaked... I pulled this 2.8L out of a car in which it ran and was driven daily for 2-3 years before it sat for some 6 months... so I know there isn't anything wrong with it, and the base timing lined up correctly, I checked it while I had it out

yesterday I started the car, drove it for nearly 45 minutes, up hills, stopped at 3 stop signs, pulled into the driveway happy that it was finally working well aside from an unstable idle, went to reverse it to turn around and pull into the garage, and it stalled out... wouldn't start, I tried several times, had plenty of power... next morning I came out and it started on the first turn or the crank, I pull it into the garage and took the plugs out and cleaned them off... went to restart it... started, ran rough, then shut off... what would cause it to suddenly flood when I get home and put it in reverse? Are my symptoms being misdiagnosed?

I'm seriously at wits end here, anything you guys have would be great...

my next stab will be at swapping the injectors back to the 2.8L ones... but I'll wait till mid tomorrow to see if anyone hits back at this thread, might be something I'm not seeing that you will... I'm assuming the 2.8L injectors will work fine with the 3.1L electronics

sorry for the long read, but thanks in advance for the advice

I'm going to go with averages here...

The injectors themselves are not likely the culprit. You can check them electrically and mechanically with a DMM set to read the resistance of the coil and a 9V battery to actuate each injector. I have a 9V battery in a small enclosure with a DPDT momentary switch, that also is used in testing audio systems, polarity of speakers, locations, etc. Doing this won't be able to test for blockages, or foreign contaminants in the injector, but you can see that electrically they are fine (should read around 12 ohms each), and that you can hear/feel them actuate when power is applied to them.

I would check to make sure that no wires were pinched when you installed the engine, this is a common thing to happen. You can use the DMM again to see if the wires are shorted to ground, and also to see if the injector driver in the ECM may be shorted to ground.

Check to make sure that the injectors are actually getting a proper signal, a noid light is best for this, but a test light can be used in it's place, to watch for a proper 'flashing' signal to the injectors.

Another thing to check would be the fuel pressure. If there is a pinched or blocked return line, the fuel pressure would raise very high, and change the amount of fuel delivered with each injector pulse, possibly flooding the engine.

sounds liek the injector grounind wire is pinched and grounding out somewere holding the injectors wide open..

also once u fuel foul out the plugs cleaning them will get the car to fire again but it wont take anything to fuel short them again, go out and get a new set of plugs. it will make things much easier

now that you mention it... there were three ground wires that attached the right rear of the engine... I may have accidently switched them from the block to the firewall... will try that then get back to you guys..

something I forgot to ask last night... prior to 85 AC 43 spark is called for, 85 to 88 (or 89?) is AC 42, and 88 (or 89?) to 92 is AC 43...

currently I have AC 43's installed, is that ok? when I replace these plugs, should I install AC 42's?

R42's in the 2.8, but you can run 43's. I used to because of fouling in my #6 cylinder due to bad valve guides.
The aforementioned ground wires are chassis ground wires, 2 being for the HVAC controls.
I tried to tell you that the 3.1 fuel injectors were too big, but check your wiring first, especially around the rear connection. I also second the checking of the fuel pressure regulator and the return lines. Once you get to know your car, you can listen to the exhaust note and tell whether your injectors are good or not, which is how I could tell that the set I got off of a guy with a T/A weren't the right size (other than the fact I got that rich code again).

the 3.1 injector wont run rish enough to foul the plugs, if nothing else is wrong, if u pinch and ground out the injector wires they will stay wide open when the car is cranking or running instead of pulsing, a noid light would be the easiest way to tell if this is happeneing

well, like I said before, swapping the injectors with the rail was just an oversight on my part... and I have no problem taking them back out and swapping with the 2.8L injectors. I found out last night that they are a B*TCH to take out of the rail though... oh man...

I have checked both main and return lines for the fuel, they seem to be alright, I didn't see any kinks or bends other than those bent from the factory... I will check the regulator next... however...

I installed new spark plugs and the car fired up immediately... I idled outside my home for near to 20 minutes... it was running fine... I got an ses light and 4 codes... 21, 23, 33, and 35...

could this be a vacuum issue? I drove the car down to the stop sign near my house, not even a half a mile away... and the car stalled out... I was able to play with the throttle enough to get it home, but as soon as I pulled up to the garage and let off the gas, it stalled again... I know that if I keep trying to start it, these plugs will foul as well... f that

I'll check the pressure regulator now... I read earlier on that I can turn the engine over and if it's bad fuel will come out of it with the vacuum line off...

after I check the regulator I'm going to install a new throttle body gasket and see if that changes anything for the sensors up front...

I'm inclined to agree with Maverick since to be honest, the injectors being too big makes sense to me... but I will keep checking other things to be certain in the time being... honestly though this car can't sit much longer, I need transportation, and this is my beater car, and I'm sick of getting 10 mpg... I save my nice car for nice days... this engine is really finicky...

u have a 3/1 speed density system u need to do the idle relearn procedure or u will have alot of stalling and such till it learns the idle

how do you do that? tell me, tell me, tell me

please?

This was my first inclination as well. I had real bad running rich problems until I reset minimum idle and replaced TPS and IAC. Also, my 3.1 would start and abruptly die b4 I did this.

You mentioned it was running rich? Did you think about the o2 sensor? Also, in my most current thread, this mod I did made my air/fuel mixture much leaner, but in my opinion not too lean:

https://www.thirdgen.org/forums/v6/4...w-mod-our.html

My exhaust smells like that of a much newer car, not nearly as noxious.

Well, lets go through the codes:

21- TPS sensor circuit. Sensor voltage high. This will cause extra fuel to be added.

23 MAT circuit fault.

33 MAP sensor circuit. If it is reading low vacuum, then there will be fuel added.

35 IAC control circuit (IAC valve). This won't add extra fuel but if the IAC is unable to control the engine speed, it will throw this code. With the TPS sensor also throwing a code these could very well be related.

So I would look at why you are getting the MAP code first and fore most. This will have the largest factor in why you are running rich. A low vacuum signal or high sensor voltage, will cause the ECM to think that the engine has a high load on it, and add fuel accordingly. Even in the low RPM column most GM code has enough fuel added at high load to stall most engines, definatly enough to foul plugs.

Your 3.1 injectors are not too big.

Let me say that agian.

Your 3.1 injectors are not too big.

If the RWD follows the same as the FWD for injector size, they will be practically the same size. IIRC in the FWD 2.8 and 3.1, both were right around 17 lbs/hr.

Your trouble codes are pointing you in the direction you need to be looking.

Forget changing the injectors I'm sure they are fine. Check the electrical side, make sure nothing is pinched.
Make sure all grounds are connected, it almost sounds like you may have missed one.
Check the voltages at the MAP sensor, there should be a 5V reference (grey), a ground (black or purple) and a varried signal (green). The varried signal should read about 5V at key one, engine off, and then drop down to less than 2.5V, probably closer to 1.8V when idling. Make sure you connected the vacuum hose, or if the MAP sensor connectes directly to the intake, make sure the little boot is around the reference port on the MAP sensor.

thank you six shooter, you've been among the most helpful so far with this project...

do you suppose that these codes could be caused by a leak in the throttle body gasket of the 2.8L I suspect it's leaking... I assume that would have an impact on the sensors mounted before it...

I also will try cleaning off the IAC sensor... is there anyway to clean off the TPS sensor?

I'm fairly certain that I haven't missed any grounds... I've run front to back on the wiring harness, and if I have missed something, it's well hidden... I count 2 grounds on the left side of the back of the motor, and 3 on the right... then of course the main ground front left... I will clean the IAC , and then install a new throttle body gasket and run the idle reset procedure and see where that sits me....