I'm chasing an intermittent stalling/stumbling problem on my car. Without getting into the details, it seems to be heat related and is more evident when the engine is under load, usually in either 4th or 5th. I'm suspecting the ignition system and would prefer not to start throwing parts at it. Since the problem on crops up when the engine bay has been thoroughly heated up (maybe 20-30 minutes of city/highway mix driving) I don't think I'll be able to test the ign module as I think it has to be out of the car to test, which will only give it time to cool down. I spent some time with the search engine and found out that the Haynes manual describes a resistance test for the coil, but I couldn't find the steps anywhere. If somebody with a Haynes manual could clue me in that would be great. If it matters, the engine is an 88 v6 5speed

What's funny is that I own one of the GM service manuals and couldn't find this simple tested detailed in it. Due to the nature of the manual they expect me to have testing hardware (and in some cases knowledge) that I simply don't have.

Thanks guys and gals

Misfire under load is a classic symptom of worn spark plugs. You should do a full tune-up first...

Complete failure after a half an hour of driving usually points to the coil or the ignition module. Unfortunatly I have no idea how to tell which it is.

If your engine fully dies when it heats up, I suggest you pull one of the plug wires as soon after as you can. Jam an old plug into it and lay it across the metal of the engine, and go ahead and start cranking the car. If it won't start still (or only starts for a moment before dying again) you can see for sure if lack of spark is the cause. After this you could borrow the coil from another older GM car and see if the car suddenly starts sparking. If not, it's probably the ignition module.

If it helps any, several of mine did this and the coil was the problem each time. But you also mention stumble, hesittate, ect, maybe a good time for a complete tune up --or winaldl will nail the problem down for you, so you won`t be throwing $$$ at it.. hope this helps some.....

I'm going to have to check on the spark plugs, but I know the wires and the distributor cap were replaced within the last year.

I've never had the engine completely die when the symptoms start up, but when it gets to the point that I feel it at cruising speed I usually just kill the engine and coast. Then I restart the engine after a minute and it is good enough to finish the last mile of my trip.

I'm sure a complete tune-up would be very beneficial, and I'm considering it a little more each day. The thing is, when this problem is dormant the car has all the power I expect it to have and once the engine hits operating temp it idles wonderfully at 950-1000 rpms (while cold it idles at 1500).

The whole situation got just a little more interesting today though. When I was leaving for work this morning I noticed that the SES light isn't coming on before the engine starts. Obviously upon further inspection I found that I can't pull codes either. I'm pretty sure it's unrelated, but something tells me I should find the cause of this first.

quote Originally posted by Toaster_Man: The whole situation got just a little more interesting today though. When I was leaving for work this morning I noticed that the SES light isn't coming on before the engine starts. Obviously upon further inspection I found that I can't pull codes either. I'm pretty sure it's unrelated, but something tells me I should find the cause of this first.

First thing to check is simply the bulb. I think you can get to it by removing the panel on the back of thr gauge cluster.
I dont think the car would run if the ECM were actually dead.

quote Originally posted by Toaster_Man: The whole situation got just a little more interesting today though. When I was leaving for work this morning I noticed that the SES light isn't coming on before the engine starts. Obviously upon further inspection I found that I can't pull codes either. I'm pretty sure it's unrelated, but something tells me I should find the cause of this first.

can't pull codes meaning? Do you still get a continuous code 12 when pulling codes?

quote Originally posted by ditch: can't pull codes meaning? Do you still get a continuous code 12 when pulling codes?

Well if the check engine light won't come on, there's no way to get codes

My car does this EXACT same thing. I have a new ignition coil on it(i've tried 3 and it still does this so i know the coil is good) and it's got new plugs and wires. I get no check engine light or anything either and the bulb is NOT burnt out in the cluster (it'll work in the seat belt or the ajar socket). Hopefully this thread will solve our car problem Toaster_Man. Right now for me it is looking like the module..

I tried getting at the SES light from the back of the control panel and I couln't figure out those little grey sockets. Do those pull or twist out through the back or do I have to take the cluster out and attack it from the front? Disillusion, I am pretty sure that the ecm would still be able to light the SES light with a bad ignition module. You might want to look at that flex circuit board on the back side of the dash. It might have a broken lead going to the light.

I'm not too proud to say that since I bought the car I replaced the clutch slave cylinder, bled the clutch, and rebuilt the alternator, but was finally stumped when asked to simply change a lightbulb. I know what you're thinking, and I don't understand it either.

they are little twist locking sockets like the taillight bulb holders and such. I know what you mean thought i've changed my waterpump, master clutch cylinder, heatercore, ignition coil, plugs and wires, installed my own stereo and the list goes on and i cant figure out this darn power loss garbage..

Aww heck. It looks like you and I are definitly in the same boat here, Disillusion. I just went out and switched the light bulbs in my SES and Parking break indicators and I'm right back where i started, the parking break light still works and the SES still doesn't. I also pulled one of the spark plugs while I was out there. They don't look bad at all; I mean it's running on the rich side, but I could have told you that from the smell of the exhaust. In fact it looked like the one at this link http://www.maxracesoftware.com/Plug_Reading_Normal_1.jpg which was described this way "The spark plug picture below ... shows the "Richest" a spark plug can be and make good Horsepower and Torque curve , any richer than this will definetly hurt Peak Horsepower mainly, but not so bad for peak Torque ."

It caught me off gaurd today when the engine started acting up about twenty minutes into the drive home. In all fairness about half of that trip was spent above 65 mph, but I wasn't expecting it on a 45* day. This time I just shifted into neutral and let it idle while I coasted down 10mph, then I couldn't get it to act up again for the next 5-10 minutes.

I'm going to borrow my buddy's spark plug light and see if I can at least narrow it down to weak spark. But I'm beginning to wonder if we shouldn't be looking towards the fuel delivery system.

Toaster_Man, I asked my girlfriends dad to take a look at it (he's very framilier with the chev 2.8 that is in our cars, and his 2.8 powered s10 did the same sort of thing our cars are doing) and he said it sounds like the map sensor might be f*cked, so im going to try and replace that tommorow(had to ship a map sensor over from the mainland) and i'll let you know if it fixes the problem. I'm really hoping it does.

That's the direction I was hoping this would take because after the spark test I am fairly confident that our problem doesn't lie directly in the ignition system.

and the long awaited up date......it runs better with the new map sensor! it still doesn't seem to have enough low end torque though...it'll move in 4th and 5th now but not as quick as i remember

Attaboy! I can't wait to get this fixed so I can concentrate on pushing my battery up front...like I was going to do 2 weeks ago. Couple of questions though (because I guess I'm too imapatient to wait and find out for myself)

When you say lack of low end torque--compared to what it had before it would go into what I am now calling "freak out mode" or compared to before this problem started? Did this fix the check engine light, or is that something I'm still going to have to contend with?

step 1
use high scale should read very high (Infinite) if not replace
step 2
use low scale should read very low or zero if not replace coil
step 3
use high scale should not read infinite if it does replace coil
The steps are out of my chiltons manual.

[This message has been edited by Jake_Dragon (edited 03-22-2006).]

Thank you very much. Looks like the test couldn't be any simpler.

Lack of low end torque as in it's gutless 4th and 5th still...before it wouldn't even go above 2000 rpms in those gears now it does but very slowly...and the check engine light is still a.w.o.l

I have done test #1 on 2 old coils and one new coil I just bought. It doesn't regester anything on my meter. You touch it to the terminal shown and then to the metal frame around the coil correct?

I didnt have time to read, but rule of thumb, if it dies when it gets hot then works again when cooled, its the coil. The module is almost always (99.5%) a one time kill, being solid state, when it fails its done for permanantly. Also the stumbling points to the coil as well, if the case is cracked moisture will get in there and cause it to missfire intermittently.

Also the coil test just gives you a dead or not dead answer, if the coil works even part of the time, it will be completely inconclusive as the test only checks for broken or shorted wires.

If I may make a suggestion????

Seen this before and it turned out the ignition module was loosing ground and it was getting hot because it couldn't disipate heat to the distributor housing. Any time I do a diagnosis/Tune up on a GM dist. I would loosen the module screws and retighten them to ensure proper grounding. It is true that ususally they are either good or bad but bad ground will make a good one act bad. Just thought I would through that in, in case you haven't tried it yet. It would be a sure cheep fix if it did work.

I guess I should have come back and updated this. I changed out the module because I found a couple cheap at the junkyard and that cleared it right up. interestingly enough, I had the module tested after I changed it out and it tested fine. I figure the thermal compound had simply passed its prime and a refresh would have had the same effect.

Glad to hear you got it fixed. I know it can be agrivating but good job.

Bob