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Author Topic: Major ignition problem
Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
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Last Sunday on track my son noticed our 91 had stumbled a time or two.
We checked for loose connections and finding none I took it out with no problems.
Second session, he limped into the paddock on what seemed like two clylinders.
Cut a long story short, We got the car home and Monday I started work.
First looked for a bad plug or lead with a timing light and found all four leads had a serious missfire.Canged plugs and wires, no change.
Heres what has been done so far with no change.
Changed ignitor.
CAS
Coil
Checked for continuity between ignitor and coil
Checked coil resistance.
Checked for short circuit.
I am really frustrated with this, the car has been flawless for eight years and recorded 116 rwhp and 106 ft lbs. just two weeks ago.
A quick note of public thanks to Steve Bertok for his time and help over the many phone calls.

JimEli Verified Driver Made Donation to Website
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Region: NWR
Car #: 5
Year : 1991
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Re-establish ALL grounds. Don't just simply check them.

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Randy Thieme
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Region: Oregon
Car #: 51
Year : 1993
Posts: 322
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A bad connection from the harness to the ECU did very similar things to my car. If you've swapped ECU's recently that's a suspect.

Jamie Tucker Series Champ

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Car #: 97
Year : 1990/99
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Change out the MAF meter! At least clean the connection and/or try a different ECU. My money is on the MAF meter.

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Bad Al Bell Verified Driver Made Donation to Website Series Champ
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Year : 1991
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There are two coils. Did you change both?
Did you check for codes?

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Year : 1991
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Check yor kill switch

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Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
Posts: 293
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Kill switch no longer in the circuit.
No codes, that surprises me. [banghead]
All 3 coil packs check good.
Did a pin out on the AFM (maf), checks good.
All grounds cleaned and continuity checked before reattaching.
Could the ECU be telling the ignitor to fire both coils at the same time?
All good points guys thanks, keep'em coming please.

Jamie Tucker Series Champ

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Year : 1990/99
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Just change the MAF! Doing a pin out will not show the problem. I have had the same problem and it is often caused by an internal failure of the MAF meter. If that does not work change the ECU. The problem will most likely be one of them.

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Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
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ECU on order. What would the MAF/AFM have to do with spark. I'm confused. [Confused]

Randy Thieme
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Year : 1993
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quote:
Originally posted by Dave Lewis:
No codes, that surprises me. [banghead]

Dumb question but does the engine light come on at all when starting the engine? If not that points to either the bulb, ECU or harness.

There are situations when enough things are going wrong at once the ECU can't report errors correctly. Last spring when I was trying to retrieve error codes while dealing with a bad ECU connector, the engine light would stay on and never go out like it's supposed to when there are no error codes to report. Swapped ignitors and then it started blinking error codes like crazy for three separate issues: AFM, ignitor, and temp sensor.

Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
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Yup, normal CEL operation. Also no CEL can mean a bad ground close to the fuel regulator. Ask me how I know.

Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
Posts: 293
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ECU and AFM changed yesterday. theproblem still exists.
I guess now is the time to tear into the wiring.
Forgot to mention, I did get a code 1, ignition pulse, But it did not come back after clearing.
My son did the pull wire and listen thing, he said 1 and 3 had a weak arc and no change in engine behavior, 2 and4 strong arc and engine died. This just adds to the confusion.

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Car #: 88
Year : 1991
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How old is the battery, how is your charging system working. A problem with either could result in your symptoms.

jj15ball
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Car #: 15
Year : 90
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Do a compression test. 8 yrs of racing could have bent a valve or two. I went through all of the electrical system of my car when I had a miss and finally decided after 3 days to check the compression. It turned out to be a bent intake valve. Its an easy check and will rule out anything mechanical.

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Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
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Battery is about 3 months old Denny and the charging system is up to snuff.
Jason, head reworke beginning of this season.
Comp and leakdown done last weekend cold.
!88/192 and less than 10%.

davew Verified Driver Made Donation to Website
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Here is what I would do.

Step back take a deep breath and put the car back together 100%. Fill all fluids. Every bolt bracket and wire, with the exception of removing the exhaust manifold heat shield.

Now start the engine and let it run for 30 seconds. Using something non flamable like glass cleaner, spray each individual runner on the exhaust manifold. A cylinder running properly will burn away the liquid very quickly. Almost instantly on a fully hot engine. The cylinders that are miss firing will have a cold exhaust tube. Once you determine which one(s) are misfiring shut the engine off. An old time mechainic showed me this trick 30 years ago.

Take another deep breath and think about the results:

If only 1 cylinder is dead, the problem is most likely not spark. Since each coil fire 2 plugs at the same time, a bad coil, wire or plug would effect both cylinders on that coil. If it is 2 cylinders on the same coil replace coil, plugs and wires with KNOWN GOOD pieces. It is possible for the igniter/ecu but unlikly.

If it is 2 cylinders next to each other but on different coils, I would look at a blown head gasket. It is possible to have a blown gasket and not loose coolant.

If it is one cylinder think about the basics. SPARK, use a spark tester, not a timing light, to test for spark on this type of ignition system. AIR, check compression and leakdown compared to the rest of the engine. FYI 10% leakdown can cause a missfire. FUEL, using a noid light check for injector signal. If signal is good, swap the injectors between 2 cylinders and see if the missfire moves with the injector by spraying the exhaust again.

Generally, igniters, ecu's, air flow meters, fuel pumps, battery, alternator etc will effect every cylinder the same. They will cause overall poor running, but not a missfire.

Each coil runs 2 cylinders, so one bad wire or plug effects 2 cylinders.

Fuel injectors will effect only that cylinder

In many cases it is cheaper to diagnose things properly, with the proper tools and methods than to just through parts at the car.

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dsrgr Verified Driver Made Donation to Website
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Whats a noid light to check for injector signal and how does it hook up???

Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
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Dave, thanks for the post. I agree with most of what you wrote except throwing parts at the car. I had all the parts ecept the ECU which I didnt have to pay for until it worked, which it didnt.
All cylinders are misfireing abouy equally so the manifold test does not work. I have done that test in the past on aircraft radial engines and it works very well.

davew Verified Driver Made Donation to Website
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To my way of thinking, you have just changed the entire diagnostic methods by saying "All cylinders are misfireing abouy equally"

Lets go back to basics.

You need air, is there a rag sucked up into the air intake tube. Seen it before, don't laugh toooo hard. Has the alternator pulley/belt rubbed a hole in the air tube? Has the flex part cracked?

You need spark, do you have enough spark, use a spark tester to prove if it is weak. Check all 4 cylinders.

You need fuel, did you get a bad load of gas? What is the fuel pressure? Fuel filter plugged? Do you have noid at all injectors? I'll explain noid later. Is the car running rich or lean? Are the plugs black? Black smoke? If it is rich, check the square green electrical connector on the back of the cylinder head. I have seen the wires pull out of the plastic connector on several occasions. You have to remove the connector and the rubber boot to look inside to see if the wires have pulled out.

You need compression, check compression and leakdown today. Last week it ran fine and the tests showed fine. This week it runs bad, re do the tests, something may have changed.

You need correct timing of various events, verify ignition timing. While doing the leakdown, verify the crank timing mark is TRUE tdc. Verify valve timeing.

A noid light is a small strobe light that plugs into the injector harness and allows you to see if the ecu is trying to pulse the injector. This tests both the power side and the ground side of the wiring/ecu in seconds. A standard test light or volt meter can not react fast enough to be of any use. There are 6-8 shapes of injector electrical connectors, so there are 6-8 styles of noid lites. I am sure NAPA etc can order them, I get mine from the expensive tool vendor who drives up every Thursday morning. All Miatas use the same one, no need to buy the set. About $25 if I remember correctly.

There are times where throwing parts at the car is the only solution. Been there and have the scars to prove it. But in most cases, logical diagnosis will find the problem faster and cheaper. Make no assumptions and gather facts, not assumptions.

Dave

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Glenn Verified Driver
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GREAT info Dave, I am printing thhese tips for future reference.

Thanks

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Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
Posts: 293
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Quick update, but first a word of thanks to Dave wheeler for the time on the phone last Thursday.
I was at my local track all weekend so could do nothing until yesterday afternoon. Took Dave's advice and checked the plug on the thermosensor at the back of the head, all OK there.
Next I started to strip the insulation off the harness that goes to the coil and found what appears to be a shield around the two wires (white and red) tha go to the coil plug, that was broken. Fixed that But found continuity between the shield wire and the white, red AND blue wire which means all are going to ground. Am I going nuts?

omg
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I feel for u dave,going through the same thing. Sorry I have nothing to say that could help.

Dave Lewis
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Year : 1991
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Misery has company David. Keep us posted on what youi find.

Dave Lewis
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Region: detroit
Car #: 17
Year : 1991
Posts: 293
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Well it seems my problem is solved. Thursday I checked the plug on the thermosensor at the back of the head. All good there.
Then I stripped all the shielding from the two wires that go from the ignitor to the coil
Yesterday, I double checked the coil towers to make sure of a good clean contact for the plug wires. Got out my ladder and cleaned my gutters.
Started the engine and it ran like the champ it always was.
Dont know which of the four rid the problem
Many thanks to all who spent valuable time both here and on the phone to help
David P, check that plug and the coil towers.

   

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