Off Idle Hesitation Stumble

[K4fxd]

Spark plugs don't look bad. Have you ohm all them to check the internal resistor wasn't broken? All my spark plugs showed 5 ohm on my voltmeter

That's 5,000 ohms. The K on the range display means thousands.

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[downtoearth1986]

I’m a little surprised by possibly being the coils. There’s 23k miles on the car. I can understand one going bad or possibly 2 at the same time, but I’ve got misfires all over the place lol. It could be and I certainly appreciate the help! Is there a range the coils should be in if I tested resistance? As you said, could be difficult to test though. Unfortunately don’t think I want to start taking stuff off a buddies car to test and don’t have another set of coils.

I’ve got a few hours tomorrow to try to dig in some more. What else can I try to check for intake gasket leak? Will be difficult to get it right at the blower/head junction. Idled pretty steady as it is now, so what should I notice if indeed there is a leak? I’m a little reluctant to try something really flammable. But I do know they would increase idle speed. By how much though? How noticeable?

Cheapest non expensive way would be swapping coils around but you could number them with a marker to keep track of the original cylinder you removed them from. Other option would be buying a new set if you can't get a hold of a set to test out.

If there is a leak the idle would change and it could hesitate under driving conditions. You would hear a hissing noise if there is a leak but it may be difficult to hear depending on the location if it's a leak. Which is why you can use a water spray bottle to check for hissing/suction noises on the areas you spray.

Spark plugs are inexpensive but I know you have 5k miles on them which is why I suggested ohm them to see if they all fall on range. Many places online recommended ohm on iridium plugs to fall between 3k-10k ohms. You would check with manufacturer ngk to verify what that should be.

Lastly 1 or 2 misfires will throw multiple cylinders readings into a misfire because the vehicle will have a hard time pinpointing which exact cylinder it is. This is why I provided the proof my car displayed with the 2 codes. 1 code stated multiple cylinders and the other code stated cylinder #1 on my car months ago. After I replaced my coil all hesitation and low noise of idle popping went away. In conjunction I took my injectors in locally to have professionally bench flow tested and cleaned for like 120.00 bucks. The tech told me it was my number 5 cylinder inj. because I had numbered them. Since then I've brought my own hand held dyi inj cleaning kit set called Allosun fuel injector tester cleaner on Amazon. These was the steps I took to eliminate and cover loose ends on my car.

 

[downtoearth1986]

That's 5,000 ohms. The K on the range display means thousands.

Correct 5k ohm

 

[Torinate]

Ok. Swapped the 1 & 3 and the 8 & 6 coils. Eliminated the catch can, scoped both 1 and 8 (they were the highest misfire count), changed vacuum hose clamps and then idled the car and did forscan logs. Then took soap and water spray and sprayed the blower to head junctions and the injector to blower areas and listened with a rubber hose. Was impressed with how you can hear more defined with hose.

But...

No changes. Same idle “pops”. Misfires galore at idle but taking the revs higher did not show any. Didn’t drive the car though. Idle has been the worst for misfires.

Mode 6 showed misfires on all the cylinders. Both 3 and 6 were the least before and now they show more. They were the “good” coils. The 1 and 8 show comparable misfires to previous log.

Idle vacuum on the gauge is +/- 20. Not indicating any sort of vacuum leak.
Spraying water and soap did not show any change to idle whatsoever. The hose picked up noises but nothing indicating any sort of vacuum leak. Scoping the 1 & 8 cylinders showed nothing. Clean and could read the numbering on the top of the pistons. Nothing out of the ordinary at least to my eyes.

Back to the flipping drawing board. Tempted to move the coils back to where they were and try again. Coil swap is quick. Of course now the car is hot so may get a few burns lol.

Going to swap them back and then do another crank relearn. Then log again and see if there’s been any change.

 

[engineermike]

Bad ground somewhere?

 

[Torinate]

Bad ground somewhere?

I’ve been going over everything in the engine bad and checking grounds, vacuum lines, clamps and haven’t found anything suspect.

Would a bad ground cause something like this? Maybe I’ll pull the rear seat and check the fuel pump and BAP grounds.

Switched coils back and ran another idle for 15 minutes doing the same things. Neighbors must think I’m nuts as it’s stinking hot here.

Interesting, mode 6 shows 1 as the worst again. 7 and 8 are the best with minimal misfires. Again only during idle. Still nothing on the soap and water and vacuum leaks.

Crank relearn is next. Can’t find it in for scan so I’ll switch over to the nGauge and do it.

If anyone has anything else to try I’m all ears. What am I missing?

 

[engineermike]

A loose ground in the coil circuit could cause random misfires. Also if you haven’t already, it might be worth trying a new set of plugs even if they look fine. I’ve had plugs go bad repeatedly and they look perfect to the eye.

 

[Torinate]

Thanks Mike. I think that’s the next step. Did the crank relearn (Misfire Monitor Neutral Profile Correction) in Forscan without change.

Plugs will at least eliminate that variable.

Pump connections and BAP were fine...

 

[downtoearth1986]

Thanks Mike. I think that’s the next step. Did the crank relearn (Misfire Monitor Neutral Profile Correction) in Forscan without change.

Plugs will at least eliminate that variable.

Pump connections and BAP were fine...

Good thing is you can eliminate vacuum leak from the list. I agree with the previous statement to check grounds and any corrosion. Is your battery fully charging? Something is causing this misfire and its even weird that it got worst when you switched coils around. Is fuel pressure solid? Did you mention before that your pcm was replaced? If so what caused the previous failure?

 

[Torinate]

PCM has never been replaced. Car has rarely seen rain - when I get caught out in it. Never driven in the winter. AFR through pulls is spot on. No fuel pressure gauge though. No codes. Have not had any battery issues. When car is not going to be driven it goes on a battery tender. Stored winter indoors in a heated garage.

Switching coils around didn’t make a difference. I switched them back and same thing.

Frustrating for sure.

 

[downtoearth1986]

Are you running 91 octane or better or e85?

PCM has never been replaced. Car has rarely seen rain - when I get caught out in it. Never driven in the winter. AFR through pulls is spot on. No fuel pressure gauge though. No codes. Have not had any battery issues. When car is not going to be driven it goes on a battery tender. Stored winter indoors in a heated garage.

Switching coils around didn’t make a difference. I switched them back and same thing.

Frustrating for sure.

This started when you was trying to make a pull a day or so ago? The only other thing that haven't been fully eliminated yet is the injectors, if coils are fully functioning, and new plugs? What fuel do you run >91+ or e85? I'm not familiar with the ngauge but will it store codes if the engine light kicks on? Reason why I ask because after you reset the KAM the issue should pop up as a code. I know with my SCT scanner it stores the codes. Sometimes a lil drive around the block will allow the code to pop up after a KAM reset. No hard driving though. Fuel pressure gauge will eliminate fuel delivery to the engine if you can rent the loaner tool from your local part store. Only thing it would narrow down to if needing replaced is new spark plugs, rear camshaft sensors(which they help regulate coil timing events), and coils. Seems like you have checked everything else.

 

[slime_bullet]

Did you do an idle relearn?

 

[Torinate]

This has been slowly getting worse. There wasn’t an event or anything like that. No. There’s never been any codes set ever. I have done a KAM reset and also crank relearn. Plugs are not new yet but look brand new and gapped at 28. There hasn’t been any change to the gap. Haven’t ruled out injectors yet.

I run 94 octane consistently. PetroCanada. Has always been great.

 

[Torinate]

Did you do an idle relearn?

Yes. Several times. No changes. I’ve done it with the nGauge and also Forscan and neither made a difference.

 

[slime_bullet]

Yes. Several times. No changes. I’ve done it with the nGauge and also Forscan and neither made a difference.

An idle relearn, not crank relearn

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