I have a 91 firebird automatic I picked up with a blown head for dirt cheap
I redid the top end and replaced the timing chain (It was very far off)
I set the ignition timing and the car started up just fine. It drops in rpm (from 1100 to about 600) when I put it in drive or reverse, I sometimes had to brake with the left foot and keep it idling with my right at stops.
The acceleration was way underpowered and it was fighting for its life to go up hill. Pedal to the floor would do almost nothing. Fixed a few vacuum leaks and one drive I lost all power in the gas pedal and ever since it does not stay idling
I have verified spark, timing, and compression. I have good fuel pressure to the rail (about 40, maintains after I turn off the car so no leaky injectors)
It has a code 13 for the o2 sensor, sounds like something I can deal with later
code 34 for map sensor or high vacuum. I believe I have fixed all the vacuum leaks and I put in a new AC delco sensor
code 42 for Ignition bypass circuit error, very unsure on this one
code 43 knock sensor error, presumably because its misfiring when it stalls out. I get a pit of popping from the intake and exhaust.

It previously ran well but now has some kind of squeaking from the engine, still squeaks without the belt on so its coming from in the engine, that sometimes goes away as if it was never a problem and comes back.
It also has some oil pressure sensor issue where it seems to thing its maxed out.
I have never seen the coolant temp sensor go up so I am lead to believe that sensor isnt reading. Wondering if it overheated on that drive I went on. I suppose the fan wouldn't kick on if the coolant temp sensor isn't working huh? I am not completely sure where it is located in this engine bay.. the last guy did funky things

I don't need anything special out of this car I just need it to get me from point A to point B. Any ideas on where to start from here would be great.
At the moment it just starts up, idles, and eventually stalls out with a misfire or two

 

Hello, and welcome to the Forum!

There are not many people in the V6 section, but there are still a few of us around. There are a whole host of issues that could be driving your problems, but let's start with timing. What Degree BTDC did you set the engine at? I know for the 2.8 MPFI, the car calls for 10 degrees advance WITH the tan wire unplugged on the passenger side firewall. If you did not unplug this wire, base timing is not set at 10 advance, more like 20 degrees retarded.

Also, Make sure that the timing is set off of the #1 cylinder, which is the passenger side front bank. I find it easier to time off of the #4 cylinder( Middle Driver's Side spark plug wire), as it is 360 degrees from #1.

Next, let's verify the TPS (Throttle Position Sensor) is accurately set as the sensor is adjustable. It should read between .35 and .7 volts with the throttle closed and the car running. This has given me drivability issues in the past.

 

I did set timing with the wire plugged in so it seems my timing will be off. I will get back to you with that voltage once i get home from work. Thanks so much

 

Okay, couple questions here.

Set timing with that tan wire unplugged, should I be plugging it back in while running? kill it, plug it in then turn it on, or should I be disconnecting the battery then plugging it back in.

Setting the timing at 10 then plugging that wire in make it so it no longer wants to run at all..

Should the voltage of sensors be taken with ignition on or with the engine running?

 

A small update, timing should be correct. Set while tan wire was unplugged.

Tps is getting about .61v so that should also be good. I don't know what the next thing to try is

 

Your timing is correct as per the mark on the harmonic damper, but, , , is the mark on the damper in the right place?

Crazy I know, , , but, there is an all too common failure of the damper where the rubber holding the two pieces together deteriorates, and allows the outer ring (with the timing mark on it) to slip out of it's proper position with respect to the inner piece (hub) , rendering the timing marks useless. If you find the engine runs OK at some other setting than what the timing marks indicate is proper, you just may want to investigate whether or not your damper has failed.

Some pics of what I describe, this one, from a 2.8 V6, had slipped SO badly that the outer ring literally fell off of the hub

 

I can say with certainty that the timing mark IS in the correct location and i have just double checked the circumstance you described to not be true in my case

 

Update, I checked the resistance of my injectors as per other forums and they all read about 10.9 with the highest being 11.3, still within range. Injectors should be good. I triple checked pressure to the rail and took the injectors out to confirm none leaking.
Car starts up like perfect, when I put it in gear it drops rpm a little bit and idles good for a few minutes till it starts surging, goes low then revs high to compensate, until eventually it chokes and dies entirely
Only check engine code at the moment is 43, knock sensor

 

Have you done an idle learn?

And the injectors can still ohm OK and be bad...

These are the two most prevalent issues with the f-body MPFI (3.1l) engines.

RBob.

 

Unfortunately I cannot just shell out the couple hundred on injectors and have that still not fix my problem. That would be devastating.

I did do the idle learn, or at least as far as I could
Battery disconnected for a minute, reconnect, starts up, let it idle for a moment, pulled e brake, chocked wheels and put it in drive. It remains in drive and idles nicely for two to three minutes before it starts choking and eventually stalls. This happens before the fan kicks on.

 

Understood. Note that the injector resistance should be checked while they are hot.

Did you finish the learn? Once it stalled, you should restart and continue. Here is a post that describes the learn. It really needs to be followed to the 'T'.

https://www.thirdgen.org/forums/v6/1...ml#post1120742

If the learn can't be completed, then need to look elsewhere. I did mention the two most common issues, the ECM is the 3rd most common issue. See if rapping on it while the is engine running changes hows the engine runs. That is a sign the ECM is bad.

RBob.

 

I figured it was worth it to fix the oil pressure sensor since it didnt work anyway so an unrelated update is that it is now reading properly.

I reconfirmed timing with the tan wire unplugged and it idled fine for me to set the timing.
I then plugged it back in and went to follow that learn sequence but was unable to finish it.
On the second attempt to turn the engine over it idled really rough but constant for 20 seconds or so, I moved it to drive and it died after at most ten seconds.
I put it back in park and try to turn it back over with no luck. The engine starts and dies immediately. It seems to be trying to idle at 500 rpm and dying before even giving itself a shot.
I can hear some kind of a pop or more like plop from the intake side as it chokes and dies.

I recognize the injectors should be checked while hot... buuut I cannot even get the engine on long enough to warm them up? I am not sure what I should do there.

I do really appreciate all the help. You mentioned ECM would be a good place to look next. Its and investment but I will get a replacement if you think thats my next best guess

 

Have you checked for a clogged catalytic converter?


Could be it can idle fine but when you need it to go a restriction in the cat / exhaust is causing ot to fall on its face


At this age, i wouldn;t be surprised either.

 

Thats an extremely good idea i hadnt thought of, ill give it a shot when i get home! thank you so much!

 

no prob! let us know!

Youll get some kind of flow out the exhaust even if its restricted, but if it is restricted I imagine (im not exactly sure) the BEST way would be to fell the exhaust flow increase as someone revs the engine for you and also snaps the throttle etc... and you should have a considerable burst / immediate increase of flow if its free flowing

 

Sorry for the delay, I went out of town for holidays and whatnot. I took the cat off. Absolutely no change to the idle unfortunately. It still seems to be trying to idle at about 500rpm, a pop or two from the intake an it dies out.

 

I read up on some success replacing the fuel pressure regulator, when taking mine out I actually found that the center rod in the spring was very bent. This gave me hope for the fix, but alas it still shuts back off within moments of starting up

edit: Ordered some new injectors and will replace on wednesday

 

Well new injectors are in.. no change..