Resolved 1G Constant Misfire

[doebelj1]

Hey guys, I've done some crazy researching about this and haven't been able to pin down a solid answer for my problem. It's a two parter, so bare with me.

I have a ton of misfire happening over the entire rpm range, boost or not. Even idle has some misfire. I've done some diagnostics and found that when I plug a timing light to the coils number 1 and number 3 fire consistently. Though, number 2 and number 4 seem to misfiring. I read that misfire on two coils means your coil pack is going. But I thought that 1 and 4 were connected and 2 and 3 were connected. Is it still possible that the 2 and 4 could be misfiring together? And that would make my coil pack bad? FYI I have brand new NGK 7es's gapped to .030.

I also noticed when I do a boost leak test the air seems to run straight through the head and right out of the exhaust. I can't find a leak anywhere, but the system only holds 3 psi. You can clearly hear it dumping into the header and running right out of the exhaust pipe/wastegate. Should this be happening? Would something like this cause misfire?

 

[DSM1G90]

ECU controls the ignition timing since it's getting its feed from the CPS, which then tells the power transistor to open and close causing the primary coils to collapse creating the high voltage from the secondary windings to fire the plugs.

And two plugs are firing in series and out of phase with one plug firing from tip to ground and the other on fires ground to tip with both plugs firing at the same time.

Honda started this dual ignition with their twin cylinder motorcycles with both plugs firing at the same time but in opposite direction.

You got a bad Power Transistor - plain and simple with one transistor (there are two of them inside the module) that is starting to short across, since it's not allowing the one coil to collapse to create the secondary voltage at a given time- it's allowing the coil to fire when it wants to-why the misfire.

Same issue happened with my Laser during the winter. Thus, replaced transistor and coil and all is good again with very smooth operation and a dead on 750rpm idle for the results.

..and the misfire could create the low psi since it's not spinning the turbo at a constant rate...but keep checking on this one.

Good luck - DSM

 

[BoostedBeaver]

If it is an electrical issue, both parts may not be defective. The service manual has a good way of testing these parts so refer to the picture below for the testing procedures. You do not currently have a DSM Profile set up (please do so soon) so the picture is out of the 90-91 FSM.

If both parts meet manufacture specifications, you may try using a noid light to see if the injectors are firing as they should. Post the results of the two test in the image below and we shall go from there.

As for the boost leak test, I would isolate the engine and intake manifold by pulling the piping at the throttle body elbow and performing a BLT from there. Yes, you will probably have to make another BLT'er to fit your throttle body elbow but this will get you closer to finding your issue. Incase you are unsure of how to perform a BLT properly, here is a link.

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Robert

 

[asexton6969]

How are you performing a boost leak test? You should be able to hold alot more than 3 psi. Also what are your mods on the car as far as I/C and piping.

 

[pearl4gtsi]

If your only getting 3 psi max on a boost leak test, there should be a large, easy to find boost leak! And a boost leak that big can cause a misfire.

I would definitely suggest the following:
1. Boost leak test and fix every leak you find
2. Check the resistance of your ignition coils(as per service manual)
3. Check the resistance on your power transistor(as per service manuall
4. No matter how new they might be, a new set of spark plugs. I've had a spark plug go bad, cause a bad miss/dead cylinder issue, and when checking spark, give some odd results.

 

[doebelj1]

There is an aftermarket I/C and intake piping, I'm just not sure of the specifications on those. When I'm driving (and the car is running well) the boost goes up to 18psi no problem. I took the intake piping off running into the throttle body and blocked off the remaining piping that led back to the turbo. It held more than 10 psi before blowing off my boost leak tester (didn't tighten it, oops) and no leaks. I'm just super baffled as too why it would be running right through the head and straight out of the exhaust without leaks anywhere

I've had a problem with the PTU before and replaced it, it definitely doesn't sound like it did when it was the culprit originally, but I replaced it again a few weeks ago with a used one I got lucky enough to find on ebay. (The 90 PTUs are rare!)

I pulled my coil pack and tested the resistance. It's a 90 so there are four connectors that run into the primary. I checked the plug, which I believe is the primary resistance and came up with these numbers:

My digital voltmeter reads .2 and .3 over when grounded against itself, it's a little used, had it set at 200 ohms for reading

Connector 1 to Connector 4: 1.1/1.2 ohms
Connector 2 to Connector 4: 1.1/1.2 ohms
Connector 3 to Any Connector: No reading
Connector 1 to Connector 2: 2.1/2.2 ohms

For the Secondary Resistance I couldn't get a reading at all on the digital voltmeter, but I used an analog one, set to R x 100 and a reading of 140 on both secondary tests... This a bad coil than?

 

[BoostedBeaver]

When I replaced my PTU a few years back, I bought it new from Autozone. It was around a 100 bucks if I recall correctly but they had them.

I suggest getting a volt meter that is accurate and can test the secondary coil.

The air could be escaping out the exhaust if the intake and exhaust valves are open at the same time allowing the air to rush out of the cylinder. If one valve was bent that could easily explain the low numbers. Not saying that is your problem but a quick compression test would tell you a lot.

Robert

 

[90gsxProjectCruiser]

Haynes repair manual,
on the connector with the 4 pins (primary resistance) you should get 0.77-0.95 ohlms between the bottom right pin (4) and the top right pin(2). you should get the same between the bottom right pin(4) and the top left pin(1). your reading might vary a little but between 4-2 and 4-1 but they should be close

secondary resistance is checked by plugging in your testing leads to the first two posts on the coil pack(closest one to the 4 pin connector) you should get between 10,300-13,900 ohlms. if it tests good there, move to the other coil pack posts and do the same test. if they test outside the tolerance replace the coil packs.

 

[90gsxProjectCruiser]

If it is an electrical issue, both parts may not be defective. The service manual has a good way of testing these parts so refer to the picture below for the testing procedures. You do not currently have a DSM Profile set up (please do so soon) so the picture is out of the 90-91 FSM.

If both parts meet manufacture specifications, you may try using a noid light to see if the injectors are firing as they should. Post the results of the two test in the image below and we shall go from there.

As for the boost leak test, I would isolate the engine and intake manifold by pulling the piping at the throttle body elbow and performing a BLT from there. Yes, you will probably have to make another BLT'er to fit your throttle body elbow but this will get you closer to finding your issue. Incase you are unsure of how to perform a BLT properly, here is a link.

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Robert

the 90' has a 4 pin primary connector, not a 3 pin.

 

[25gtalon]

Replace the coil pack it sound like a bad coil pack borrow one from someone and test. I had a similar problem and I replace it problem fix. I am using a standalone ECU.

 

[DSM1G90]

Got my stuff from Rockauto and true, the PTU was around 90 bucks.

From what one wiseman told what he did with his PTU ... he took the unit off the bracket and coated the base side of the PTU with "heat sink" grease so the heat from the PTU can transfer quicker to the mounting plate to reduce the heat that the PTU builds up during operation. Thus, when I got my PTU, I had some "Arctic Silver" heat sink compound - stuff one uses when building computers to mount the heat sink fan on top of the CPU - and did the same trick. I was also looking in adding a computer heat sink fan on top of the PTU to aid in cooling the device down.

When I did my test on the PTU, one side had indeed shorted across due to the test light stayed on. This shorted transistor was feeding constant voltage to the coil and heated one of the primary windings causing high resistance readings - why I replaced both devices.

Zero reading on that one coil definitely shows an open primary coil.

-DSM

 

[doebelj1]

Well I forked up the cash and bought a new coil pack today, no difference. I had a brand new voltmeter right out of the package and it gave me the exact same readings as the old voltmeter for both the new and old coil pack (it wouldn't read the secondary resistance at all on either).

I ran a compression test a two days ago and had 140 on number 1 and 150+ on numbers 2, 3, and 4.

I traded out the PTU for another one I bought and had in there before trading out the one I have now, no difference. I'm not sure how to test those but I'll try to find it on here. Though, I don't believe I have 3 bad PTU's.

I have a brand new set of high performance coils, so I switched those back for the stock ones, no difference.
I re-gapped my plugs to .025, no difference.
I pulled off the valve cover to check the rocker arms and Cams, they were fine.
I drained the oil and fished around for any shavings, there were none.
I checked the wiring for the O2 sensor, thermostat sensor, and CAS sensor, all were fine.
I pulled the MAF while the car was running, it bogged down pretty good and threw a CEL, believe that's fine...?

I hooked up the timing light and found that instead of number 2 and number 4 misfiring, number 3 was the only one, and it was misfiring pretty badly. I have a stock ECU that still has the seal on it, I'm gonna put that in and see if it makes a difference. If that doesn't work I'm not even sure where to look next

 

[doebelj1]

I went ahead and changed the ECU, again no difference. I also checked my PTU using the light bulb test, it came out just fine. I did find that my spark plug wires weren't closing all the way on top of the plugs, it helped a little but there is still misfire, and she doesn't like to boost worth a crap; the gauge will read 12psi, but it feels like its pulling 2. I also had some other NGK 7es's. I switched the plugs all around to see if I could get a combination that works, there wasn't one. I'm completely at a loss here

 

[90gsxProjectCruiser]

not 100% if this will help. maybe try to switch the misfiring cylinders injector to a different cylinder? if its glogged or squirting instead of spraying maybe you could try to see if the problem moves to another cylinder with it? anyone else chime in on this??

 

[90gsxProjectCruiser]

did you notice a difference between that plug and the others? did it look like that cylinder was more burnt, or even wet like its flooding

 

[BoostedBeaver]

Blindly throwing parts at a car hardly ever fixes the issue the first time around get very expensive and normally frustrating.

Your motor needs four things to operate: Air, Fuel, spark and Compression.

One of those factors above, Air, is verified by doing a BLT. You attempted one and it failed. You need to fix this issue before throwing more parts at the car.

Compression was verified when you did the compression test and seems to be in working order.

For fuel, you must verify that the injector is receiving a pulse width from the ECU. To do this, pick up a noid light (rent from autozone). Unplug the injector and plug in the noid light. it should blink.

If it has electricity the you have to ensure the injectors are working properly. Test the resistance of the injector and then something like this can be used to test them. This will also clean them to some extent.

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Lastly, you need the proper amount of fuel pressure.

Spark is the electrical monster that requires a ton of trouble shooting. Verify the ones above and fix your boost leak first.

Robert

 

[DSM1G90]

Have we checked the CPS any?

 

[doebelj1]

Blindly throwing parts at a car hardly ever fixes the issue the first time around get very expensive and normally frustrating.

I agree with ya there. I was super reluctant to purchase it, but the ohm tests coming out indicated it was bad. Live and learn.

The CPS sensor has been checked with the "starting it and seeing if it spins test." I'm not sure if there is another one that would more accurately see what it is doing. I also regapped my plugs to .027, I'll try pulling them back to .030 tomorrow, though I had them there before it didn't seem to help.

I found one major problem that I can't believe I let slip by. My EGR valve was still connected and had only one vacuum line running to it from the intake. Without thinking I switched the vacuum line the other day from one of the pin holes to another. I ran a boost leak test today and air started pouring out of the other pin holes. I covered the pin hole that the vacuum line used to be on with my thumb and sure enough the pressure would dump right out of the system into the exhaust, only holding 3psi. I'm not sure why or how that works but I removed the valve and blocked it off with a THICK piece of iron, no more leak.

Though, that did open the door to a few more leaks. I fixed most all but one that seems to be coming out of the throttle cable; like the bearing inside is bad or something? I can't find a way to fix it. System holds 15psi now though, but I'd still like to know how to fix that leak.

It drives and sounds better but still misfires. I reset the ignition timing after the block off, and then checked the spark plug wires with a timing gun. Number 3 is the only one that misfires, and pretty badly. I changed out the plug in that cylinder, no difference. I switched around the spark plug wire, no difference. It definitely misfires and although it drives decent it still lags and sputters like it isn't getting enough fuel. I'm going to check the injectors tomorrow but the misfire spark on number 3 is baffling...?

 

[DSM1G90]

How are you testing for misfire .. first seeing if the spark is being 180 degrees off than No.1 ? Odd is that No.2 isn't giving you fits as well since the two are connected from one coil - just one is firing backwards.

There is one theory that can pop up in mind: Do you know anything about "crossfiring?"

Crossfiring is when two plug wires are laying next to each other in parallel and when one wire gets energized, the magnetic induction from that wire travels across to the one laying next to it and can cause that wire to be energized with firing that plug along the original one-and the plug could be the one that firing out of order..

I've seen picture of 4G63 motors with their spark plug wires all but where they should be to prevent crossfiring - why the arrow marking stamped near the spark plug ports on the head cover - and the have to be a certain way in the wire loom when heading back to the coil.

I've seen some where the wire loom was all bundled together and wrapped up in a zip tie. others, wires laying across the head since that a good path to ground and electricity is very lazy: it will find the shortest path to ground no matter what.

Now, not saying that these areas is how your setup looks like, or similar, but this is just a wonderment on this No.3 issue of misfiring.

I had a similar issue with a 4G37, AND with it's No.3 cylinder: I changed cap, rotor and wires and still no cure. ECU was good along with the ignition module. No. 3 was sparking real good, but still a grumpy No.3 cylinder misfiring. Thought I was experiencing crossfire. Redid the wire loom to get all wires far enough away, but still no cure. Thus, went to the last resort: changed the sparkplug out ... and that was the cure: I had a bad NGKBPR6ES-11 plug, and it was only a month old that had just barely suffered a hairline porcelain crack at the base and it was dead shorting to ground. Switched that plug out and all became good.

-DSM

 

[BoostedBeaver]

.025 is too close of a gap.
Compression can blow out the spark being that narrow.
Gap needs to be .028-.030

This is incorrect. A smaller gap makes the spark "stronger" since the distance that it has to travel is less.

As the gap becomes larger, it is more prone to spark blowout. If you experience spark blowout at the stock gap, the recommendation is to decrease that distance.

To the OP, you could also swap out your injector to see if that changes the misfire. As for the leak at the throttle body, its going to most likely be the throttle body shaft seals. Here is how you fix it.

http://www.dsmtuners.com/threads/1990-eagle-talon-sleeper.427853/page-2#post-153104752

Look at post #44 about half way down.

Robert

 

[DSM1G90]

Thx for the updated information - worth remembering. DSM

 

[DSM1G90]

Question: What would be the reason on narrowing a gap below factory specs? I never did this practice with any of the vehicles owned.

thx - DSM

 

[curt-s]

Have you verified that all the wiring AND the PTU/coil plug connectors are in perfect working order? Vehicles this old suffer from corrosion, petrified shielding which can cause breaks, and the little tabs within the wiring connectors breaking off, making only intermittent contact. I've suffered from all these, causing misfires and all sorts of problems.

The last one is the one that really caused a huge issue.

 

[Calan]

Question: What would be the reason on narrowing a gap below factory specs?

To get a hotter spark that is less prone to blowout, for whatever reason. A lot of people running big boost, different fuels, or various ignition systems will lower the gap for more consistent ignition.

I believe I was running .023" before tearing the car down, but at one point I had to gap them down to .019" to prevent blowout.

 

[doebelj1]

Sorry this one is so long, I'm trying everything.

I checked the voltage on the plug that connects to the coil pack and it came out to 12.46; my battery tested at 12.64. I also had a problem with the PTU plug before, so I hard-wired each one of the wires individually into the PTU, those all grab on there very snug.

I had thought about the crossfire as well too. I bought a spark plug wire holder for 2 bucks down at the part's store to keep them from crossfiring, made no difference.

I also changed out the plug in cylinder No. 3 and cleaned out the ground spot down there just to be sure, no difference. I have a handful of NGK 7es's and even had a few Denso plugs that were new, none of them worked. I'm thinking I might try out an NGK 6es in the No. 3 to see if that helps.

I've been testing the spark on the cylinders with a timing light gun. I connect it to spark plug wires No. 1, 2, and 4, and it fires consistently; the light blinks each time it fires. However, when I connect it to No. 3 the light blinks sporadically, and you can hear the misfire. I've checked it with different spark plug wires and different plugs, making sure to watch for crossfire, again no difference.

I checked the resistance on the injectors, they all came out to 6 ohms. I also checked for power on the injector plugs, all the right side connectors on the plugs came out to 12.46 volts. All the left side connectors on the plugs came out to 11.54 volts.

I did another boost leak test and only found the throttle cable spot again (I'm working on that).

It drives okay, but feels like it isn't getting enough fuel and has a hard time gaining speed. The boost gauge reads up to 12 psi when you get on it, you just can't feel it. You can also hear the misfires and when I decelerate it back fires like crazy. I found a spot on my flex pipe for the exhaust busted open pretty good and welded that. However, when I put it back on, the other side was leaking; I think I need new exhaust piping (it looks like 2 1/2" all the way back, no Cat). I also decided to check and see if the fuel pump has even been tampered with. The guy I bought it from SAID there was a Walbro 255 in it, however, I've never actually checked... When I pulled the fuel pump cover off it looked completely untampered with. From what I've read, you would be the luckiest person in DSM history to get the fuel line fitting off without stripping it or contorting it somewhat; the fitting looked like it had never been touched.

I also only have a stock fuel pressure regulator and RC 550cc injectors, fuel filter is brand new... I'm not sure how any of the fuel system could be effecting my spark in number 3, but it might explain some of the sputtering and lack of power...?