Engine Miss at idle when engine is warm

[Guest Brolliar]

I have a 1989 Reatta with less than 50,000 miles that has recently developed an engine miss. It doesn't miss when the engine is cold but starts missing when the engine gets warmed up missing at idle and low rpms. The ECM, engine module and coil kit were replaced in 2004 which was about 7,000 miles ago. The plugs were replaced last week with no change. Thinking the ECM was again bad it was replaced last night with an parts store part but didn't cure the problem.

Now checking the engine with a timing light that measures the spark near the coil without connecting into the plug wire circuit, the light blinks on and off in a normal pattern until the miss starts and then the light blinks irregularly for two plugs.

Now my question, if the plug wires were shorting out somewhere before the plug wouldn't the timing light still blink on and off normally?? Does this mean the coil, ignition module or some part before them is bad or could it still be a plug wire problem??

My son and I kind of think it is the ignition module that is bad now but are not sure.

Any comments or suggestions would be appreciated.

[jonlabree]

Have you changed the wires???

[Ronnie]

Look around the base of the ignition module for a gray gooey looking substance. That would be one indication of a bad ignition module.

[wws944]

Sounds like it works ok in open loop mode, and starts acting up in closed loop mode. Wouldn't this fact rule out the ignition system?

[Guest Brolliar]

We have not changed the wires. We thought the timing light info probably meant it was a spark problem. Thought even if the plug wire shorted out the light would come on.

Open loop vs closed loop??? The car is at my son's house and the repair manual is there also and he is out so at present can't check the open vs closed loop.

The ignition module did have some black stuff oozing out of it in 2003 when it was bad but not now.

Considering getting a noid ( $8.00, a bargain, at advance auto) to check if all the injectors are getting an electrical signal to inject fuel.

[padgett]

Which two plugs ? (1-4, 2-5, 3-6,...)

Suspect that when it goes into closed loop and the mixture is leaned out, a weak coil is the problem. Might check with an ohmmeter across the terminal pairs, all three should read the same.

I do not have a good opinion of the Magnavox ignition, prefer the Delco.

[Guest Brolliar]

Thanks to all for their help. Padgett, 3 and 6 were the problem plugs. In checking the ohms all three pair read the same, 12 ohms. Switching the 3 and 5 plug wires improved the feel of the miss some. I am familiar with your interesting ignition module page http://padgettp.com/cars/coils.htm and Delco preference. This ignition module and coil pack is a magnavox.

I think the plug wires are probably the original so the Reatta deserves new ones. It has been and is a great car. Then after new wires and a good noid check on the injectors if it still misses I guess it needs a new ignition module. A little surprised one would go bad in 8,000 miles and seven years.

Again all comments and suggestions are very much appreciated.

Edited July 9, 2010 by Brolliar
Corrected my error on listing pagett's ignition/coil web page (see edit history)

[wws944]

I wouldn't replace the wires unless they are proven bad. One quick check: Start the engine and look at them at night. If you see a 'light show', they need replacing.

Padgett made a good point about firing leaner mixtures in closed loop mode. It could very well be a weak coil in the coil pack. Is there a FLAPS that can test it for you? And 7 years ago, was the coil pack replaced? Or just the ignition module?

[Guest Brolliar]

wws944, seven years ago after the coilpack and ignition melted and shorted out my Buick dealer replaced the coilpack and the module and retested the system. The car still read a missfire on cylinder 3 and they replaced the engine control module (ECM). They then drove it 27 miles and it ran great. They also replaced all six spark plugs as part of maintenance service.

We also think it may be a weak coil but the plug wires are 21 years old.

My wife and I bought it in 1994 with 22,000 miles after falling in love with the body style and the dash computer. The previous owner was a real purist who xeroxed the owners manual so he wouldn't get the original one dirty and kept it in a friend's garage since he lived in an apartment. He only drove it on weekends. He was an Egyptian software expert and only sold it when he was transfered to Paris.

What is a FLAPS??

[padgett]

Friendly Local Auto Parts Store - AZ, Boys with Vigor, etc.

When replacing the wires, get at least 8 mm. My experience is that coils show up first at 50 mph in lockup, wires and plugs at lower speeds.

They probably gapped the plugs at .060. The Magnavox seems to like .045 better. Delco Rapidfire #3s. With the Delco Ignition, I use Rapidfire #14s at .060. A wide gap stresses the rest of the secondary ignition system.

Magnaxox coils should measure 11k-13k ohms, Delcos about half that, so assuming there was a k missing yours sounds ok.

Coils fire pairs of cyl so if you isolated to 3-6 then any of two plugs, two wires, and one coil could be the problem. Sounds like you eliminated the coil and found a minor difference when swapping a wire. Sounds like the next step should be to change out the wires. No big.

Do not know which alternator you have but the wires go around a large frame and under a small frame. Running under a large frame will pinch them.

[wws944]

...My wife and I bought it in 1994 with 22,000 miles after falling in love with the body style and the dash computer. The previous owner was a real purist who xeroxed the owners manual so he wouldn't get the original one dirty and kept it in a friend's garage since he lived in an apartment. He only drove it on weekends. He was an Egyptian software expert and only sold it when he was transfered to Paris.

Sounds nice!

What is a FLAPS??

Friendly Local Auto Parts Store.

[DAVES89]

Padgett seeing as you live in Florida, I always thought when you said FLAPS you meant FLorida Auto Parts Stores. [FLAPS]

[Ronnie]

What would be wrong with just calling them auto parts stores?

[padgett]

Less typing. Also I consider the chains different from the professional parts houses.

[Guest Mc_Reatta]

In answer to one of the original questions, seeing the miss (a hitch in the regular flashing of the timing light strobe) only tells you that there was not sufficient current running through that plug wire to be picked up by the trigger coil of the light to trip the strobe on. Does not tell you why the current wasn't there. i.e no ignition signal to coil, weak coil, bad (open) wire or defective (open) plug. If the wire or plug is shorted directly to ground, you will still get the stobe light to fire, as the timing light can't tell if the current went through the plug gap to ground or not, just that it went to ground somehow.

[padgett]

However if only two siamesed cyl are affected you can be reasonably sure that is it secondary ignition (coil, plug wire, plugs) and not primary (CPS, ICM, harness). One of the things I dislike about the Magnavox is that you cannot simply change one coil but my feeling is that from what has gone before is that it is not the coil.

If you have a couple of extra wires, you might just replace those two & see what happens.

When the blue car acted up (was hard to get over 25 mph) I just replaced all of the wires with an 8mm Bosch set from AZ. That was two years ago.

[Guest Marty Russell]

May I suggest a possible cause for your problem as I experienced a similar problem with my 1990 Reatta a few months ago. It started and would run fine when cold (open loop). However, once it warmed up and sent into the closed loop, it would not run properly. I replaced wires, coil pack and everything I could think of, but to no avail. Finally, after sharing my problem on the forum, one of the members suggested I might have a bad/defective Crank Position Sensor (even though it had been recently replaced). Sure enough, I purchased another CPS, installed it and the engine ran great. Prior to getting the information from the forum, I was under the impression that, if the car would start, the CPS could not be defective and had not given any thought to replacing it again. While this may not be your problem, I did want to share this information with you.

[Guest Brolliar]

Mc_Reatta, thanks for your comments about the timing light. Marty your comment about the crank position sensor is interesting. When ours went out years ago one minute my wife was rolling down the road at 40 mph and the next minute the engine stopped and the car coasted to a stop and would not restart without a new sensor.

Padgett, I went to FLAPS (AZ) got Bosch 8mm plug wires and a loaner noid kit. At dinner with my son and his daughter - our wives are both out of town - it rained cats and dogs and the temperature came down. Last night my son changed the plug wires and checked the injectors with the noid. The car now runs like new with no problems, but the temperature is down from the rain. The noid also said the injectors were getting a good electrical signal. Now we just need for it to heat up today so we get the final test with the engine hot. I'll post the results after it heats up.

Thanks again to all for their help.

Edited July 10, 2010 by Brolliar
spelling error (see edit history)

[Guest Mc_Reatta]

To give yourself a little more confidence that you have found the problem, measure the resistance of the wires you removed. While the actual reading will vary by length and by brand/composition, they should be in a range of approximately 6K to 20K ohms. More importantly wires of similar length should be similar in resistance.

See if you don't have one that is significantly higher or lower than the others. Value also changes with temperature, so one that is marginal when cold can be much worse after engine heats it up.

[padgett]

I'd look for burned/pinched spots also.

[Guest Brolliar]

Well it is now hot in north Alabama. Just got back from watching my granddaughter slalom racing (autocrossing) She is learning event by event and doing pretty good. That was fun.

Now the Reatta - The good news is it is not a daily driver the bad news is that with the heat the miss is back. With new ECM, plugs and plug wires doesn't leave much to replace. Problem still seems to occur on plugs 3 and 6.

Earlier it was mentioned checking the ignition module/coil at a FLAPS. Do some FLAPS do that?? Of course their is also the crank positoin sensor that Marty mentioned. Also I guess the wiring to and from the ECM.

[padgett]

Might be a good time to swap some plugs and run a compression check. Never say never but with only two cyl affected it does not sound like a CPS. ALso I would wonder ablot a failing injector exept you said you could see a change in the ignotion tester.

This is where a scope really is handy.

[Guest Brolliar]

To recap: The miss, when the engine was hot, was there with the old plugs. The plugs were changed a few days ago and when the engine gets hot the miss is again there. For both sets of plugs the miss is gone when the engine is cold. The timing light shows nice uniform blinks that vary with the rpm on all the plug wires, the old wires and the new wires, when the engine is cold. As the engine heats up the light blinks become erratic on 3 and 6, being most noticeable at an idle, and with 3 being the worst. THe noid lights up and shows the injectors on 3, 6 and the rest of the front bank are getting a signal even with the engine hot.

Last night the 3 coils on top of the magnavox ignition module were rotated as a unit 180 degrees which changed the plugs the old 3 and 6 coil was driving. This did not move the miss to two new plugs. The miss stayed at the 3 and 6 plugs which we think means the three coils are OK and the ignition module may and I say may be bad. The Auto Zone (AZ) here says he can check some ignition module/ coil packs off the car but by the time the part is off the car it is no longer hot.

I guess it could be a compression problem but then not sure why the timing light blinks like it does once the miss starts. Padgett I appreciate your comment on the CPS as it is a harder part to replace. Do wish we had a scope.

Next week I plan to look for a good used Delco ignition module at a jyard and see what installing that does. Also plan to repeat the noid injector test today.

On open loop vs closed loop is there anything that changes that could change the spark??

Thanks again to all for their help. Again any and all comments very much appreciated. This problem has turned out a little harder to solve than I had expected.

[padgett]

Well the spark advances according to a different map and the mixture leans a bit.

[Guest Brolliar]

Hmmmm, the spark advances according to a different map. Do you know where the map is located?? In the ignition module?? If the bad part isn't the ignition module it seems to us that it has to be something that provides spark varying input to the ignition module. Since the miss occurred with two different ECM's we think that rules out the ECM. Repeating the noid check of the injectors today showed good results no matter whether the miss is there or not.

[Ronnie]

I have just read through this thread again and it seems the source of the miss is pinned on the ignition system based on erratic flashes of a timing light. I have never found that to be a reliable way to find a miss.

A better way to find a miss (without having access to a diagnostic scope) is to have an assistant put the car in drive and put a load on the engine by holding the brake while pressing on the gas pedal until the miss occurs. While the car is under load and missing, pull each plug wire off one at a time and replace. You will be able to tell when you remove the wire from the cylinder that is missing.

The ignition system may very well be the problem but don't overlook the MAF sensor as possibly being the source of the miss. A lot if times the MAF is the cause of a miss that starts after the car has warmed up.

I would still put my money on a bad crank position sensor or a bad ICM as being the cause of the miss.

[padgett]

OK, just for S&G what is OLDPA3 (ED17) doing when it is missing ? I'm still leaning toward a dirty injector but could be a knock retard.

[DAVES89]

I think that peiodically one should remove the ICM/coil pack and clean up both the ICM mounting plate and the botton side of the ICM. Just recently, [within the last week or so] my red Reatta started acting up [wouldn't start on first crank] on cold start/first start. Because I was going to take that ICM/coil pack off the red to put on the black Reatta [see posts on No start black Reatta] I was surprised at how much corrosion there was on the plates since I did the Padgett Delco upgrade 3 years ago. Keep in mind that while this car is also a daily driver, it is a summer only daily driver.

Something to think about when you start getting hard starts and misses.

[Guest Brolliar]

DAVES89, padgett and Ronnie I'm now sure an engine miss can at times be a complex thing. Thanks for your recent comments. We put in a new Duralast ICM under the old magnavox coil pack and the miss changed in character but did not go away. Maybe it is a dirty injector or crank position sensor or knock retard, or MAF or corrosion around the ICM. From looking at a lot of other posts concerning Reattas with a miss their seem to be a lot of possible causes. Padgett I'll check what the OLDPA3 (ED17) is doing when it is missing. And I'll read up more on what changes when you go from open loop to closed loop.

I also have a new problem. The air con compressor decided to blow its front seal and it's clutch is toast. Together they made a lot of smoke while driving checking out the miss yesterday.

In a way I miss the way engines were when I drove a 47 Pontiac convertible, bought with paper route earnings, back in the 1950's when I was in High School. For the spark you checked the point gap and condensor, plugs and plug wires and distributor cap - coils almost never failed - and to see if it was getting gas you looked down thru the carb. Oh well we do get better gas mileage now -- but at 20 cents per gallon gas cost was not much of a problem then.

My mechanic/son will be busy with other tasks for about a week so our post on the final solution may not come for a while. I'll be busy reading the service manual and previous forum posts about misses:).

Again thanks to all for your help. One thing we didn't have in the 50's was all the expert help one gets from Forums like this.

[padgett]

a) For a/c stuff several here have used TechChoice - talk to Gregg or Jerry and mention the Reatta forum for a good price on a new compressor.

Most of the cars here have been converted to 134a and work fine.

c) In 1967 gas was 20 cents/gal but a new Camaro with 327, 4 speed, and a/c was $3000. Change has mostly been inflation.

d) belt that bypasses a/c is

Gates #060725/6pk1840

AC delco #6k725

Goodyear #4060725

e) Florida has four seasons: Cool, monsoon, not-so cool, and hot. The order varies & is occasionally windy.

f) might also check the vaccuum, a leak could make the idle rough.

[Guest Brolliar]

padgett, thanks for the info on the a/c stuff. True most of the gas cost change has been inflation. I bought the six year old Pontiac convertible for $275 then. Wouldn't it be funny if after all of the parts installed it was just a simple vacuum leak. I would be very happy with that easy fix. Obviously we put too much emphasis on the timing light change but the light change was clear to both of us. We knew the two of you were discounting the light data but decided to still try the ignition monitor change.

When the Reatta first indicated a problem it was much as you described on your Bonneville on your Ignition monitor page padgettp.com . My son's wife was generally driving the car then and I don't think she noticed the mild miss but told my son the car had started bucking under load in high gear and low rpm at about 50 mph. Then as that was being diagnosed it started having a clear miss at idle.

You clearly describe the Florida weather. My son worked on the shuttle at the cape until he moved back to Huntsville two years ago and my wife and I visited Melbourne a number of times.