I've got a '91 RS 3.1L. Let me give some background info; I got the car a year ago, it ran fine for quite a while, even if the service engine light would come on when starting and (for the most part) go away after the car had warmed up, no problems honestly. Then, one night driving back from a friends, the hesitation started. I barely made it home, it was really bad. It'd die at every turn/stop, start fine, but needless to say it wasn't doing good. At first I thought it was just that I had ran out of gas. (the tank gague is really odd in my car, I mostly use miles driven instead) Filled it up with gas the next day, was still hesitating, got warmed up and ran fine. Figured that was the end of it, and that I had gotten low on gas.

Well, it kept doing it, less, but it was still occasionally doing the hesitation on full throttle, which honestly isn't a big problem in most cases. I changed the plugs, wires, rotor and distributor cap, which honestly solved nothing. I also ran some seafoam through the brake booster line, but not in the crankcase.

A week later, I went to Maaco, shut it off, and left 15 minutes later, more hesitation, stalled after starting, and then stalled at a stoplight not even 300 feet away from the parking lot, had to wait about 10 minutes, it fired right up, and I went home, no problems at all. This is where I started getting confused, how can you troubleshoot a problem when you can't get anyone who knows about it to see it? I've taken it to a mechanic after pulling a few codes out, and he fixed two of the problems (throttle position sensor and coolant sens. too high) and suggested that if it persists to bring it back again. (The codes I got were: Coolant sensor too high, Throttle position sensor too low, and Electronic Spark Control failure)

It also refused to start once. I turned it over, it stalled after sputtering, and then ran about 5 minutes later flawlessly.

Well, it happened again, and this time I wasn't driving, it was my dad (his truck was being painted) and it did the same thing, stalled, started up 10-15 minutes later. I went up to the post office fine, but on the way back more hesitation. What bothers me most is that I've checked for spark and I've checked the coil and they've been fine, but how could I even tell if that's the problem when it works most of the time? I hate irregular problems

 

my t/a went through a similar thing when the fuel pump took a dump, something to check out...

 

You can't that's the problem. Mechanics can only fix problems that they can duplicate.

Fuel pumps are not uncommon to give you problems similar to this as well as ignition coils. What I suggest you do is carry around a can of carb cleaner with you and the next time it dies and won't restart, open the air cleaner and spray the carb cleaner down there, then crank it over. If the car runs and then dies when it exhausts the carb cleaner supply, then you know you have a fuel delivery problem, otherwise, it's a spark/ignition problem.

 

Well, one thing I should have mentioned when I said it dies and doesn't start is that it actually fires some when it starts, but it only turns over a few times and dies again.

I will grab a can of carb cleaner and give this a try though, thanks for the advice.

 

Yeah, sounds like a fuel problem. That's how I deal with trying to figure crap like this out at my shop. Very successful using this method.

 

Earlier tonight I washed my car and was going to start it up and take it to the garage to wax it, and it wouldn't start. So, popped the hood, poured a little bit of gas into the throttle body (yeah, didn't get any carb cleaner, completely forgot about that until now ) and that did nothing, so I had my dad check for spark while I turned it over, and he believes it's the ignition control module, as his truck did the same thing to him. Going to pull that out tomorrow and take it up to Napa and hope they can test it, or I'll just get a new one.


I really hope it's the ignition control module, anyways. A lot cheaper to fix than a fuel pump..

 

Have you even had the fuel pressure checked yet? Before you jump to the fuel pump, for starters, eliminate any obstruction in it's path... clean your injectors thoroughly, and replace your fuel filter.

Also, you mentioned you threw a code for the Electronic Spark Control failure. Like your dad said, replacing the ignition module is a great idea... but have you replaced the ESC sensor itself? You might want to check the wiring in it's connector as well, as varying weather conditions can be brutal on them, resulting in poor readings.

 

Yesterday I got the ignition module out, had it tested at autozone, came out fine. Took it back home and cleaned a bit of rust off of it and the rest of the distributor, replaced the cap/rotor, and it seemed like the problem was fixed, until today.

The service engine light started blinking and the engine kept cutting out, and then finally died, but it didn't start back up for a good 30 minutes this time.

I'm going to replace the fuel filter and oxygen sensor while I'm under the car, since I'm sure it has never been replaced. I also regularly run injector/fuel system cleaner to keep everything clean, and I also ran some seafoam through everything but the crankcase about a month ago.

Also, Street Lethal, I was told that the ESC really shouldn't be the problem here, even though it wasn't working right, what exactly could poor ESC readings cause?

 

Oxygen sensor is a good idea to replace on general principle, but it's not going to fix your problem, I promise.

The ECS system is for sensring and controling pinging/detonation. If the Knock Sensor is bad, it'll give you this code, but the only symptom you'll notice is that the engine pings. I've never seen it cause stalling or no starts.

I've never trusted getting an ICM tested because they tend to fail only when hot, which is not the case when bench testing. Just get a replacment and install it, it'll save you lots of trouble trying to diagnose this. The only sure-fire way I've ever been able to test an ICM is to hook a test light up to the negative side of the coil primary. When you crank the engine, the light will flash if the ICM is grounding the coil properly.

 

What I just found quite interesting, is the listing of information sensors that I had just come across. I initially mentioned ESC, as I had a similar problem with my '86 (when it ran fuel injection), and a faulty ESC sensor was the cause of similar symptoms...

I'm now looking at my 3.1's diagram, and I'm not even showing an ESC sensor. The information sensors are as follows; O2 sensor, TPS, CTS, VSS, MAP, MAT, PSP (power steering pressure) and a/c pressure switch. The controlled devices are as follows; fuel injectors, IAC, fuel pump relay, ignition coil, trans. clutch connector, coolant fan relay, EGR, a/c relay, fuel canister solenoid...

Interesting.

Getting back to the problem though, have you checked fuel pressure yet? I would give the "entire" fuel system the once over, including the pump, relay, injectors, corresponding fuses, along with the oil pressure switch. Again though, we're shooting arrows in the dark without knowing the fuel's pressure...

 

Haven't checked the fuel pressure yet (Also really don't have any means of doing so myself), but I honestly don't think that's the problem. It was running as strong as ever, if not stronger today, for most of the day. Except we pretty much re-created the problem on our own, not at random, drove it hard for a while, came back home and let it sit for 30 minutes, sure enough, right when started it was idling rough and wanting to stall at idle. This was when we decided to replace the oxygen sensor (it looked fairly new on the outside when we were swapping the fuel filter) and reset the ECM error codes. We couldn't recreate the problem again.

Could the error codes from the bad throttle position sensor and other problems we had a mechanic fix a few weeks ago sitting in the ECM have caused the engine to act like it did?

Also; When we took the ICM to get tested, the guy testing it told us that he normally runs them 6-8 times to get them hot to see if they'd fail, could it be that when they get hot and start to cool down it would just flat out fail until fully cooled?

 

The minimal heat made from the electronics inside the ICM isn't enough to make them fail. If you can touch it and not have VERY hot fingers, it's not going to fail unless it's totally dead.

Remember, they sit on a plate inside the ditributor cap, it's very hot inside a closed engine bay, on top of a peice of metal. I'd say 250*+. I've had, and heard of, too many ICMs "testing" good at AZ or NAPA and the like, and having them actaully fail when they're in the vehicle to trust that kind of testing done by someone who doesn't know how they work.

 

In reference to fuel pressure, all you need is a pressure gauge. They sell them at your local Pep Boys. But now that you changed your fuel filter, that itself could have been part of the problem. The O2 sensor comes into play when the engine reaches closed loop (closed loop usually enables around 95 degrees, but then fully takes over once normal operating temperature is achieved)....

To be quite honest though Ravenant, when the mechanic resolved two of the three error codes (CTS and TPS), I'm sure the majority of us assumed that he reset the computer by disconnecting the battery for a few minutes. The only way to be sure now (now that you reset the ECM), is to drive it for awhile... and let us know how she's keeping up with you in the coming days.

If it happens again, although not likely, you'll definitely want to check the pressure. It's no biggie, in fact, I try to check all three of my cars' pressure when I give them their monthly tune up (I run them hard)...

Take care!

-Lethal

 

I had a problem kind of similiar once. The 2 most popular theories were the o2 sensor, and the ingnition coil (possibly having a hairline crack, which moisture could get into, causing problems.) It was very cold and wet though too at the time. I don't know what kind of weather you're having.

I replaced both and fixed the problem.

 

If you have an electronic EGR ,it's the EGR... Check if the solonoids are responding corectly. If not then the unit is causing it's own vacume leak at the top of the unit....

 

Well, I've been driving it for a few days, and I have to say I think it's working fine now, the only issue now is that when I brake quickly the engine tends to bog down, like it's idling low or something, except once I come to a stop it idles fine. Since I reset the ECM, should I need to re-calibrate the new TPS?