New to board could use some help.

My son recently bought a 86 Iroc 305 tpi. The previous owner said it needed a fuel pump. After getting the pump changed we have a bad idle and it will not accelerate. Could this be a bad tps? I mean you can floor it and it just sputters and won't pick up rpms. Could it be running off just the cold start injector? I did notice if we would cover the bellows coming from the maf sensor that the idle would smooth out, but hit the throttle and it just sputters and will not rev.I will check the tps volt readings tommorow as my dmm is at work, also is there a quick and easy way to hook up a gauge to check fuel pressure? Any and all help would be appreciated, Thanks

 

Welcome.

If you cover the bellows and the idle smooths out, that leads me to think you have a vacuum leak there. Getting that fixed will make the car run much better.

You can check the TPS voltage at different throttle positions, should go smoothly from about .54-4V from closed to WOT. If not it might need to be set or replaced. Check out some tech articles linked from the main page, such as https://www.thirdgen.org/tpimod2 (I just linked this for someone else so I had the link copied!)

You should be able to check the fuel pressure at the fuel rail near the rear passenger side of it.

Lots of people have problems with the MAF sensor too, so if you suspect that you can try disconnecting it and seeing if it runs better. It would also help to see if there are any codes stored in the computer which could direct you to a problem. You can see how to do that here: https://www.thirdgen.org/service-eng...ht-error-codes

 

I should add that there is no o2 sensor hooked up as the previous owner put Super comp headers on and didn't weld a bung so the wire to the o2 sensor is unhooked. It has fuel at the rails as you can accuate the pintle on fuel rail and fuel comes out. Just don't know how much pressure. Would like to help the boy out with some help from you guys.

 

Thanks for the links, I have printed them and some others, as well as printed out several wiring diagrams I have work tomarrow but will get on it as soon as I get home. It is flashing the check engine light and will try to access the code and will post the findings. Thanks again.

 

Have you checked fuel pressure? Just want you to verify someone didnt accidently install a tbi fuel pump..

 

Thanks for the links,

Update,

Checked fuel pressure at the rail, 48 psi, also cheked the tps .579v @ idle position and 4.21v @ wot. Checked the tps input at the pin outs of the ecm and got the same numbers. The car was towed to my sons home and all we have done is change out the bad fuel pump and filter. The engine barely starts and hardly idles it will not rev and throttle position makes no difference. I hate for him to throw parts at this, Years ago I had a simular problem on a carbureted engine and it was a bad condensor. Could this apply to a tpi also? If the module in the distributor is bad would it even fire at all? The only codes we pulled were 22 and 33 those could have come from us troubleshooting i.e unplugging vac hoses and tps. After clearing these 2 faults none have flashed up again. Like was stated earlier he bought this car from a fellow who told him all it needed was a new fuel pump and the o2 sensor hooked up. Is there a special way to index the disrtibutor to get the injectors to fire corectly? I'm stumped and need a comprehensive plan of attack. Thanks for any help, Mo

 

I have the same problem with my car ive been throwing parts at it the last 4 weeks. i can tell u that the o2 sensor will not do anything to air/fuel mixture till the car is warmed up also if u can cup ur hands over the intake and starve the engine a little bit and it seems to run better it must be something in fuel/air mixture. so its doubtful the ignition has problems. ive got the exact same problem to a tee. my thread is call"my beauty wont run" its on this tech/engine board. look it up ive got all the thing ive changed listed. it has me baffled. but i can tell u ive chekd all my sensors and even changed my computer which didnt help. if you find the problem please fill me in....

 

If the ignition module was bad it probably wouldn't fire. But I have had one or two that were dying and behaved similarly, they eventually died and the car wouldn't fire at all.

The injectors all fire at the same time (or in banks, I forget) in response to the ignition module output. If you've got fuel your problem has to be spark or timing related (supposing that you have compression).

The first things I would check now are for proper timing and that you are getting good spark at the plugs when you turn the engine over. I recall reading that autozone can test ignition coils and/or modules so you might try giving them a call.

 

Thank you,

We will try the module checks and coils, just seems like it is starving for fuel. We are running it open headers (long tube Super Comps) now as he had to drop the exhaust and track bar to remove tank. What a p.i.t.a. You say the module has something to do with the "batch fire"?

 

Rezinn is right,the TPI unit fires in 2 banks, left and right side. If you put your finger on one of the injectors on either side of the engine and can feel or hear it clicking, then that bank is firing. They alternate back and forth when they are running. Sounds more like a timing problem as they said, throw a timing light in there and see what you get. Good spot is 6-7 degrees advanced.

 

Try starting the car with out the MAS plugged in, if it runs better check for leaks in the intake...had a similar problem turned out that i installed the lower plenum gaskets wrong I was getting a leak so the MAS wasn't getting much air flow and the car would idle rough...swapped the gaskets and ran fine

 

I had a problem like that but it had a rough idle then stalled and shut off. turned out to be a fuel pump dying.

 

this may sound kind of silly since it already runs, but try spraying some starting fluid in the tb while it's running while holding the tb open and see if the rpm's pick up, that will at least narrow it down to weather or not it's a fuel problem. Have you checked pressure running and at wot?

 

I think thats a pretty good idea, or check the plugs after running it. If they are wet, its an ignition issue I would say. Or it could be terribly rich.

Since the o2 sensor is disconnected, its probably running in open loop all time, which means its running on set parameters in the comp and not gathering any info from sensors except the engine temp. The engine runs richer in this mode for cold starts and at idle on some cars. Not sure about tpi's. If its that rich, you should be smelling an enormous amount of fuel while its running.

 

hopefully he got it fixed by now, it's been a few months...