Engine running problems

[orange02ss]

I have an 82 FI spider. The cars has been running good lately although I have had this issue before. I started up the car the other day and it was idling as I was moving stuff around to take it out for a drive. It then died (does that sometimes when its cold), then this issue started as I couldnt get the car to start again.

With everything as is, the car will start (long cranking) and run for about 3-5 seconds and then die. If I unplug the MAF sensor the car will idle and rev (not all the way but around 3000rpm or so). With the MAF plugged in and the coolant temp sensor disconnected the car will start and idle, although it will not rev. I have swapped out the MAF with a new (re manufactured) one and there is no change, I also just replaced the temp sensor again. The car was having these exact same issues about a year ago but i tracked it down to the temp sensor which was intermittent. The last time this happened I was living in Texas (the car is on Guam) and it pretty much sat for 4-5 years as nobody could figure it out. I am out working on Guam right now so I went through it last year and got it running good. Now its doing the same thing again??? I cleaned the wire harness ground on the intake manifold. Last year I went through everything (checked the fuel pressure etc..) I dont think its the fuel pressure as it will rev when the MAF is disconnected, I also checked the cap, wires and rotoe (replaced last year). Any ideas??

[narfire]

If it has been sitting, I'm gonna suggest the fuel system. Hows the fuel? Stale? perhaps rust in the tank and that has got into the fuel pump giving it intermitant flow. Fuel filter bunged up, not sure if water in the filter would bung it up but perhaps worth changing out,same with the fuel. If it ran in the past just fine,I'd like to think the sensors would be fine. Pessure regulator? Then injectors. Pull the cold start valve and watch it as you crank, it should flow for a few seconds.
Anyway thats a start.
Good luck
Chris

[orange02ss]

Its been running fine the last year, it was prior to the last year it sat.

[rlux4]

You've already checked the usual suspects for your symptoms (AFM and temp sensor) so I don't have the answer right off hand for you. A couple of things might help though. If you haven't changed the O2 sensor already, you should. It won't fix your problem, but will help attain good fuel/air ratio when the car is running. They are cheap and available anywhere. The only other thing that comes to mind is the ECU. They rarely go bad, but I recently loaned my spare out and the wrong one was returned to me and it was bad. It was an "oops" and he shipped mine back to me right away. You'd need a known good one to check this possibility. And it's probably not the culprit, but it wouldn't hurt to check the function and setting of the TPS (throttle position sensor). You'll find the method here on page 49:
http://www.artigue.com/fiat/books/Artig ... 124_MM.pdf
If you don't have it already, here's a good diagnostic manual for the system:
http://www.angelfire.com/wa2/fits/index.html#ljetguide
Ron

[orange02ss]

Thanks! I have checked the TPS and I had an extra computer that I swapped out to check with no luck. I even checked the pinouts for the MAF and temp sensor at the ECU plug and they checked out good. The TPS was acting a little weird but I don't have my Fluke with me and I am using an el cheepo meter, would the TPS be a culprit? or would it affect performance more, as in off throttle and on throttle?? Seems it wouldn't cause this problem even if it went out. I also checked the dual relay for power going to the pump and it was getting good voltage. I am searching for my old fuel pressure tester to check that but I am assuming its not it as the car will rev with the MAF disconnected but ill check it anyway. Any other ideas? I do need to replace the o2 sensor though. Thanks for the links!

[Pembroke36]

I am new to Fiat and I am not familiar with the exact system that your car has. But an ECu without a MAF reading will go to some constant, default map, causing it to idle, but not rev. No temp sensor could give you some output, but cause another default mode because the ECU does not want to run too lean without knowing the temp of the engine. I would think these are both working showing the change when they are unplugged. A TPS that is faulty could cause this exact condition. It reads air and temps, adjusts fuel with the injectors, but the air is not adjusting the right amount because the throttle is not really where the sensor says it is. This could cause long cranking and no idle. If the ECU in this car is really this sophisticated. I work at a Mercedes dealer as a tech and I have a hard time realizing every car is not setup the same way sometimes.

[rlux4]

You're right, the TPS's function is to signal the ECU when you're off throttle or WOT. It's unlikely to be the problem, but because the ECU responds to it's signal by varying the pulse and duration of the injectors, I suppose it's minimally possible that it could get a signal from it that would mess up the signal coming from the AFM (our cars don't measure air mass as in a MAF, the AFM measures air volume and temperature.)
You may want to check the resistance across the arc of the scraper under the AFM cap.
I'm stumped for a definitive answer, sorry.
Ron

[orange02ss]

Well, I figured it out! I finally found the fuel pressure gauge and hooked it up to the cold start injector hose. When I started the car it would run but no fuel pressure would register on the gauge?? Weird, so I pulled off the tester and left the hose open and cranked it, no fuel. There is gas in the tank and the fuel pump is turning on, so I figured I would check the filter. I pulled the hose but nothing, so I jacked up the car to get a better look at everything and then the fuel started pouring out. I put it back together and cranked it, now it has pressure, starts up and runs good! I guess there was some kind of air block (like a vapor lock) or something, who knows!