Hey guys, so im out of a daily driver right now and need to get this figured out...87 Iroc LB9. Drove to work, car ran perfect. Started to drive home and couldnt get over 1/4 throttle and she falls on her face. Long story short, tested TPS and it was at .58 at idle but at WOT stops at 2.50 Volts. So i swaped out the TPS With a new one and have the same numbers...54 at idle and it smoothly goes up as i increase and it stops at exactly 2.50v. Checked the wires at the sensore, all looks good and i have 5.08 volts from the ecm (which is new btw). Just for whatever its worth too..2 weeks ago she got a new distrubutor and ecm..also threw the fuel pressure gauge on and all is well.
Im probably wrong but it just seems odd that it stops at exactly 2.50v, i guess i was thinking if it was a wire issue it would fluctuate a little. Both sensors do it. I even pulled the ecm again to double check the connections and all looks very good. I just cant get over 2.50v from either tps. Any ideas on where to start? Could this be some sort of limp mode indicative of a completely separate problem that's not TPS? By the way, not sure if it helps but 1, im reading all this through a scan tool (snap on mt2500) and 2, there are no codes at all, no check engine light. I jumped out the ecm for the self check and got the code 12 just repeating like normal. Kinda figured something that makes it fall on its face over 1/4 throttle would set a code. If i floor it the engine completely cuts out until i lift off the pedal. Idles perfectly though.

 

Ok quick update, i just probed it the old fashion way with a volt meter right into the pins and all is normal. Im actually at .64 at idle and 4.34 at wot. So either the mt2500 only reads to 2.50 volts or the ecm is actually only seeing 2.50 for some reason..but the sensor is working and at the pigtail, everything checks out. Also, just to be sure i double checked fuel pressure...36 at idle..45lbs with vacuum line off..so id say the pump and regulator are fine. Bliped the throttle a few times and fuel pressure is strong but she absolutely falls on her face and anything over 1/2 throttle the engine almost shuts off..as soon as i let off she idles fine. Wtf?

 

Just a thought, have you checked your MAF? Is it original? I was having some weird pig rich/long start ups when engine was warmed up. Also occasionally I had similar symptoms to you, car wouldn’t idle and would die if not constant pedal and ran terrible in spurts but it was very isolated. Turned out the original Bosch unit would work fine when cold but when the engine got up to temp etc the sensor seemed to flake out when hot, like a heat soak etc. Replaced with a Delphi unit from rockauto and that cured it. Btw no trouble codes either, good luck.

 

How about them injectors?

 

try a fuel pump leakdown test. had a similar issue when my fuel pump blew up. it would run ok at idle but wouldnt do much more. it would back fire, stumble and stall out while driving. good luck

 

How exactly do i do a fuel pump leakdown test? All i know is ive got good fuel pressure and it holds when the car is off. 36 psi at idle and goes up when i hit the throttle. Not sure how it could be a clogged filter and still have good pressure even under load. Even in park just free reving she stumbles and if i floor it it just cuts out. I dont think a bad MAF would do this. Just wondering why in the hell the ecm isnt setting a code. Sometimes i hate OBD1

 

I would look at your MAF. Symptoms sound like it. Is it the original Bosch?

 

Yeah as far as i know its the origional. Wouldnt a faulty MAF set a code? Whats the best way to check it? Something i can do with a volt meter at the connector like a tps?

 

In my experience, a bad MAF does not set a code. The car just becomes jumpy above idle and can die.

 

I extracted some the more helpful 89 Service Manual pages for you. Attached.

 

If you do decide to try a new MAF I would stay away from the auto zone/advance crap, I tried that first before I went with the Delphi and it immediately threw a code and did not run right. The Delphi works good and no codes. If you do a search on here a lot of guys have had issues with subpar aftermarket MAFs.

 

When my MAF went (and when I've unplugged it) it does throw a code.


*EDIT* - ignore the markings on this chart, the person who forwarded it to me had marked it up to help my situation.

Took me a while to find through my threads of constant fueling problems. I'm no where as well versed in these engines, but when my car was running and stumbling and falling on its face, this chart gave me the solution (which was the pump) but it offers a few other solutions.

 

Any chance youve got page 2 of that?

 

Agreed. Try to replace with genuine Bosch hot wire.

 

So just for grins i unplugged the MAF. With it unplugged it set a code, idles rough but now i have all the power back when i hit the gas. So, problem solved. Just would have though it would throw a code..aparently not always. Anyone know where to find an origional bosch? Ive googled and cant seem to find one. Best i could find was a delphi from rock auto, all the rest is autozone crap. Couldnt seem to find one on hawks either

 

Gotta love TPI, all is not what it seems when diagnosing check engine lights with these cars most of the time. Let us know if the Delphi cures it.

 

Anyone know the best place to get an origional bosch MAF sensor? Is the delphi just as good?

 

There are usually a few used ones on eBay but as with anything on there buyer beware. Other than hawks which you said did not have anymore your best bet is probably the Delphi IMO. If you think this is bad try rounding up EGR parts for these cars, that was a nightmare.

 

I just remembered this place, if you really want a Bosch these guys might be worth a shot. They specialize in 3rd gens

http://www.camaroheaven.com/