I own an 84 Fiero sport coupe and it flat out refuses to start when the engine is hot. It's the worst when i've been on the highway for awhile and let it sit for more than 15 minutes. If it's been off for less time than that it usually starts right away, and if it's been sitting for over an hour it starts easier, but still not right away. the car has a slight misfire in park but other than that the engine is in good shape so far as i know. I replaced the Spark plugs, fuel filter, distributer, rotor, and plug wires when i bought the car (~6 months ago). I'm totally baffled by this. please help!

most of the time I see this..... it's the starter, or battery. could be other stuff, but most times has been the starter, or the battery, neither of which like allot of heat.

what happens is that heat from the engine, and cat converter, soak them with heat. Hot batteries don't put out as much power. Hot starters take far more power to spin up.

1. make sure ALL the batery cable ends are tight, and clean.

2. replace all cables that have any damage. even if it looks slight. cables are cheap.

3. replace the batery, especially if it is more than a couple years old. Batteries are easy to get to, and cheaper than starters most times.

4. replace the starter.

even if the car is turing over do all the first 3 items. when cranking the starter motor draws so much power that there might not be enough left to properly energize other systems. A starter on it's last legs can make things even worse, even if it's spining up. You want to save that for last because of cost. ((The battery should be replaced any time a starter is, it's just not worth the hassle. A bad starter can damage a battery, and you don't want to be messing with it again in a week when the battery dies.))

I had the same problem with an '84 and replacing the starter and battery solved the problem completely.

actually, the engine turns over fine.. in fact it often has to turn over for quite a few minutes before it starts. it seems like fuel just isn't reaching the engine.. I'll try your suggestion's, been meaning to get a new batt anyways. thanks for the help

Hmmm, my 84's engine wouldn't turn at all when it was hot...

still sounds like some sort of heat soak problem. is it a 4 or 6cyl?

Hey guys. Just a thought,but I used to have problems with fuel line vapor lock in older English sports cars. Usually a little isopropanol or similar fuel additive to clear moisture out of the fuel system would clear up the problem. In extreme cases I've even had to insulate or reroute the fuel line. Although I've never had this problem in fuel injected cars [higher fuel pressures] I guess it's possible,especially given the high engine compartment temps. found in the Fiero.

I've tried a few additives, stp and seafoam, and they didn't seem to help.. it's a 4 cyl

Did you try replacing the ignition module?

try driving the car a bit to get it hot, and then park it, and lift the tail deck. this should let the heat go straight out, and keep it away from things like the battery, and terminal block. If it's something on the engine block, it may take longer to heat soak, but should still do it.

I always hate these type problems....

Just like to add my $.02(Cdn) worth...

My Fiero is an ‘87 with the 4 banger, 5 speed, and distibutorless ignition system. I've had it for more than two years. Among the several "frustrations" I have had with this car, I also have a problem similar to what is being discussed here. I live on the west coast of Canada where the climate is quite temperate. Doesn't get too hot or too cold. In the winter I don't have a problem starting the car at any time. But now that the weather is warming up a bit, if I try and start the car when the engine is HOT, and ONLY when the car has been sitting for 15 minutes or so, two problems actually occur, probably related. The car is difficult to start, and when it does start, stepping on the gas has almost no response, it's a very DELAYED response. The idle speed is all over the place. The only way I can get the car to move is to try repeatedly to rev the engine, and when the revs finally do go up, I then drop the clutch and start moving. If the tranny was an automatic I'd never get going! Once the car is moving, it takes less than a minute for it to behave properly. This is definitely a heat related issue. And to repeat what "Standard" has stated above, this is NOT a problem with the battery, starter, etc. The engine turns over just fine at any time, hot or cold. Other than this problem, the engine appears to run alright. The car will act like this until late next fall when the weather cools down again (unless someone here knows the solution!).

Any suggestions, short of replacing "everything" individually to find the problem?

-Patrick

patrick,

my guess... the MAP sensor. if it was TPS, or injector, I think you'd be stalling alot. It sounds like the ECM is keeping the mix right, but not seeing the vacume changes from the MAP.

I have slight version of this problem, and mine is an AT. It stalls in reverse, and sometimes it's just flaky in drive. It started after I changed the MAP. I havn't had time to stick the old MAP back on. (I have a habit of removing decade plus sensors, I think I may have gotten a bad new part. It happens.)

Patrick,

Actually, that is a good idea... Replacing everything! ;)

(sorry, couldn't resists - back to the serious answers again)

Hi Guys,

Thanks for the quick responses, although I'm not too sure about Cliff's solution.:)

Ogre, from looking through the postings here, I have to assume that you know a few things about Fieros. That's great. Knowledgeable people at these forums are a valuable commodity. To help educate myself and other visitors to this site, could you please answer a couple more questions .

If the MAP sensor is malfunctioning at any time, would this not be picked up by the ECM and displayed as trouble code 33 or 34? And even if this sensor only appears to malfunction when it is hot, would not these trouble codes be remembered and still be displayed when the MAP sensor was cool and functioning "properly"? Or am I being too trusting in the ability of the ECM to display trouble codes pertaining to every malfunctioning electronic component?

Any responses to these questions would be appreciated. Of course, this could result in Pandora's box being opened, and a flood of questions pertaining to Fieros might follow.:)

-Patrick

fiero isn't that much diferant that any other GM car as far as what the engine controls do. In short No, don't trust the ECM codes completely. For example I had a code 45 every time I turned around. Turned out to be the injector was just tired, and not seating completely, that after checking every thing else.

Looks like I found some of my warm flakeys today..... Recently I replaced the EGR with an after martket unit. (Wells brand if I recall) It has a little plastic elbo on it... the little plastic elbo is a turd. it creeps off slightly and leaks.

Actually Cliff's comment "replace everything" is Quite sound on a 10-20 year old car. All the sensors are old, and worn.

As for the MAP specifically, yes it can be not working correctly and not set codes. a partly blocked/leaking vacume line to it will delay it's responce enough to cause performance problems. It's also posible for the line to leak only when hot. the rubber ends soften a bit when warm. if they are already weak....... The thing has to be pretty much dead to set code allot of times, but it can be off enough without a code to be a problem.

Also diconnect, and plug, both lines to the vaporcanister, at the TBI. Also check the brake booster line, EGR line, etc. eny of those cause intermitant leaking.

Check the bolts at the base of the EGR. because AL expands diferantly than the iron EGR it has a nasty habit of comming lose. If either bolt turns remotely easily then replace the EGR gasket. The EGR can also bind when it's hot failing to close completely when it should.

I'm a little late in replying, but my car does almost exactly what Patrick described. It's getting worse now that it's starting to warm up here in Minnesota. Mine's an AT and it idles all over the place after it refuses to start. I have to sit and rev the engine a little and wait till it settles down or it'll nearly stall. and thanks for all the responses! I'm so glad I wondered onto this site. Best thing I've found so far! thanks again!

I checked my Service Manual and found a whole bunch of things that could be causing these problems. You might want to try and find a Pontiac dealer who has a diagnostics computer (scan tool) so you can narrow it down.

Even a badly insulated tach filter could cause this problem! If one of the wires is bad, it will cause smaller sparks at the sparkplugs. A hot engine will start easily, even with small sparks because the fuel evaporates almost immediately when it enters the cylinder and therefor ignites almost spontaneously. A cold engine also starts easily because the ECM switches to "cold start" mode. But an engine that isn't cold nor hot...

Then again, I could be completely wrong!

I was discussing this very thing with someone last night on another location. he'd noticed the tach gone nutty before the thing failed to start......

the sort form. Yes a tach filter can cause this. the simple test is to unplug the filter. This will disable the tach, but it should run now if the filter is bad.

The tach filter, as we've discused else where, contains resistors, and capaticors. The way the filter is wired, if a cap fails as a short circuit, a common failure with caps, it shorts out the control feed from the dist module to the coil. This usually doesn't do any permanent damage, but it shure as heck won't start.

(cliff, or who ever had it, please email me the secmatic you had, I collect them. I've been told several are "exact" duplicates. theogre@sprynet.com)

A bit of ignition theory: (I have limited Fiero specific resources, but other GM data seems to confirm it.) The Dist Module controlls the sparc thru 500RPM. The dist module controls the change over to the ECM, Not the other way around. (the DIS system is the same way. The coil controller manages the change to ECM running.)

In pre87's there is a pink lead that supplies power to both the dist module, and coil at all times the key is on. (my book say the same colors for both 4 & 6 cyl)

There is a white wire that connects the "control" terminal of the coil to the dist module, and the tach filter. This lead passes thru 2 resistors and out of the filter to the tach.

Inside the filter 1, or 2, capacitors tap this wire, and connect to ground.

To fire the coils the dist module, either by itself, or at the direction of the ECM, Breaks the Ground from the control lead of the coil.

If the caps in the tach filter are shorted, power will flow to ground thru them, bypassing the dist module. the coil will not fire. (or will fire weakly if the capacitors are alightly resistive.)

Keep in mind..... Computer controlled coils work basically the same as point controled coils. They fire when the primary winding's path to ground breaks. The 'hot' side of the coil primary winding is 12-15Vdc at all times the key is on. (I don't see a ballast resistor anyplace in my schematic.)

Thanks for the responses guys. Of course, this now leads to further comments... :)

Cliff, no offence, but I had to laugh to myself when you suggested finding a Pontiac dealership to help narrow down the problems. Over the last 25 years, I've always worked on my own cars. Every one has been a Chevy with V8 power. The Fiero has been the first car I've owned that has fuel injection and all the computer stuff on board. It's also the first car I've ever owned that failed the emission tests here. (There's something ironic about that.) I tried and tried to get the Fiero to pass with all the tricks I had learned over the years, but I finally had to admit defeat and I took the car to a Pontiac dealership for their mechanics to deal with. Well, $400 later I returned to the testing station where the Fiero not only scored worse on the emission tests, but the damn thing wouldn't even idle properly. Because I had spent the money at a "Certified" repair center, I got a conditional "pass" for the year, but what a friggen joke. I had to undo what the damn dealership mechanics did to make the car run better. A year later I went to an independent shop to try my luck. They determined that the "cat" needed replacement. I replaced it and the car actually passed the smog test legitimately. This is probably what it needed the year before. So much for any faith I have in GM's "factory trained technicians". Another year has gone by and the Fiero is due to be tested again. It's going to be interesting to find out if the "cat" is still doing it's job.

Ogre, thanks for your advice. It would seem to me after reading your post that it would be a good idea to simply change ALL rubber hoses in the engine compartment BEFORE changing any electronic components. If nothing else, it would be a relatively cheap way to eliminate some variables.

One statement you made that puzzles me a bit was in reference to disconnecting and plugging both lines at the TBI that lead to the vapor canister. Is this something you're suggesting to do and then to leave that way, or to do as a test and then to re-connect? I'm betting on the latter, but I just thought I'd double check.

-Patrick

Patrick,

Nononono, you got me all wrong! The only reason someone should go to the dealer is to use their diagnostics computer (unless ofcourse you have your own).

I know having them try to repair stuff is blasphemy! ;)

Why let the dealer mess up your car for a lot of money, when you can mess it up yourself for free? :D

yes, I ment at a test. that eliminates all the steel lines, the canister, and it's nasty little valve on top.

Replacing the rubber lines is a good idea. BTW you can find some of those rubber connectors for the hard plastic lines as well..... Motor Mite line has them. Pep boys carries them. they are in the section with nuts & bolts.

When you are looking for vac leaks, don't forget to checkout the break booster to.

Thanks Ogre, I'll be checking everything out.