Hlvo13

so on my 89 formula 350tpi I finally gave up and took it to a mechanic, it is running poorly, it is sputtering and dies after a few minutes, so I was thinking mass airflow sensor or ECM, the mechanic has told me ECM, mass airflow sensor, or distributer. any ideas? the car will fire up run at a high idle, then when it idles down it sputters bouncing from 400rpm-1200rpm and when driven and you step on the gas it doesn't fire you can feel the injectors fire, at least I think but I'm stumped and don't want to throw $650 worth of parts on it just to see if that's what is wrong. it has normal fuel pressure and the pump is brand new. thanks for any help y'all can give

aliceempire

iTrader: (14)

The mechanic sounds like he's stabbing in the dark without troubleshooting. What's been checked or tested? I'd be looking for vacuum leaks to start. Any codes?

keykey

Why were you thinking MAF or ECM? Is it just a guess? Guessing is a the most ineffective and expensive way to diagnose a computer controlled engine control system with lots of sensors, relays and actuators that the engine depends on to run correctly.

If the mechanic says ECM, MAF or Distributor he's just guessing too. Go to another mechanic who doesn't use guessing as the preferred diagnostic method.

Did you measure the fuel pressure once and think It's good all the time, or did you see the good reading on the pressure gauge while the engine runs bad?

Most important of all to begin diagnosing the problem, do you have any trouble codes?

Hlvo13

yah I don't think he has run the codes yet, im going to throw the mass airflow on it because ive been meaning to its running really rich and I once forgot to plug in the mass airflow and it ran just like it is now if that's not it ill probably try someone else, I really want to buy my own code reader but haven't had any luck finding one in my price range, ill post what happens after the MAFS and go from there

vetteoz

iTrader: (13)

Got a paper clip ?

https://www.thirdgen.org/forums/tech...s-dumbies.html

You must have $$$ to waste

Even if you get a MAF fault code showing it could be a power , wiring or ground problem ;
not just that the MAF itself may be faulty

Read
http://www.chevythunder.com/maf_code_33.htm
http://www.chevythunder.com/maf_code_34.htm

Hlvo13

so he's throwing a code reader on it today but yesterday I put a mass airflow on it and it ran fine except the tac was all over the place. I ran it around the block and gunned it a few times and she ran fine shut it of and turned it back on a few times. then like 10 min later I went to take it out and it was back to running terribly, missing and running so rich. any ideas im thinking the ECM but we will see what codes it gives me. if yall can give me any more advice or hints or what ever it will be much appreciated. thanks

keykey

I've been working full-time in a shop every day for 8 years now, and so far I've had TWO cars in those years that had a faulty ECM. One Mitsubishi Galant (non-start, saw a burnt component when opening ECU cover, replaced with scrapyard ecm and car ran again) and one Mazda b2600 (car ran like ****, diagnosis showed low voltage on +5v feed to sensors, opened cover and saw leaking capacitor. sent ecm away for repair, got back and car ran well again)

Broken or faulty ECM/ECU's is EXTREMELY rare. So that would be the last thing I'd guess being broken. You need a reason to suspect it, what's the reason? Do you have any measured signals, data, voltages or something to back up that the ECM is the culprit?

Hlvo13

It keeps giving me a throttle position sensor code, I've already replaced that but I'm going to see if it was a faulty one I'm not sure at this point

jazzdadss

Did you set the TPS when you installed it? Years ago when I did mine it had to be adjusted.





Once you get the proper setting (0.540VDC +/- 0.075VDC or 0.465VDC to 0.615VDC for MAF equipped cars, 0.710VDC +/- 0.050VDC or 0.660VDC to 0.760VDC for non-MAF or Speed Density equipped cars), tighten the sensor up, then recheck to make sure you didn’t move it out of range. I have found that the closer you have it to the middle setting (0.540VDC for MAF or 0.710 for SD), the better your throttle response will be.

You may just have a bad ground.

Hlvo13

I had set it to .5, im not sure at this point im just starting to get desperate I haven't driven it in almost a year and I ship out for boot camp in just over a month so its done nothing but cost me money and force me to bum a lot of rides, and being in college the money factor is excruciating. I was told that if its not a bad sensor then its the wiring harness

Hlvo13

bump