Misfire, where do i go from here. (Page 1/18)
Dukesterpro FEB 09, 10:45 AM
So in the process of my new headlight system I have been attempting to iron out my 84.

Story time. Will keep simple.

Bought with bad clutch, fixed clutch, ran good from august to October.

Started misfiring at load in October. Lugging or toeing in 3rd or 4th gear and it continually misses on all 4 cylinders.

Clutch broke again, never got to it.

Fixed clutch again and installed new plugs, wires and coil (all AC Delco).

Started driving. Same misfire is better but present. Now get a bouncy tach. 2 weeks go by and then a lifter collapses.

Take apart front of motor, replace flat tappets, pushrods, rocker arms and rocker arm pivots. Break in procedure. flubbed intake gasket install cause I RTV'd it and was using coolant. misfire is present.

Finally get around to fixing misfire and intake gasket. Replace gasket with new blue felpro unit. Replace TPS, Replace ICM. Now wont stop high idling. (vacuum leak???) exact same misfire. Oddly enough outside of the very specific condition it misfires in the car seems way up on power. Its only during toe in from cruise or during lugging that it bucks and pops. Sometime out the intake. Never violent bangs it just feels like its just a bit behind. Capped off everything but the MAP and the EGR. Still no change. When cold starting the idle is low and rough. Hard to start when cold. Needs gas pedal. Its still very, very drivable and seems to run well on the highway (85mph plus under half throttle). But if you toe into it on the highway it starts to shudder.

I can run it at wide open throttle but sometimes you have to step down, buck misfire, let up and then step down again to get it to not misfire.

Another question the engine when running makes a whistling sound (a soft, whoooooooooooo that varies with engine RPM), nothing out of the ordinary, its always had this. Is this a sound the EGR makes. Older carbureted iron dukes don't seem to make this noise.


Where do i go from here? It doesn't appear that my intake is leaking (brake cleaner check).

Clogged cat, clogged fuel filter, bad 02? I have read almost every article on the matter on this form and it usually the TPS and ICM.

Please Advise, sorry for the block of text, just wanted to provide as much information as possible.
ArthurPeale FEB 09, 02:29 PM
it sounds like some kind of timing issue. One that creeps up when there's a higher load on the engine.

When you had it apart, did you check out the timing chain? Perhaps it's stretched enough so that at lower use it's "fine" but with a bit of additional strain it becomes apparent.
Dukesterpro FEB 09, 03:20 PM

quote
Originally posted by ArthurPeale:

it sounds like some kind of timing issue. One that creeps up when there's a higher load on the engine.

When you had it apart, did you check out the timing chain? Perhaps it's stretched enough so that at lower use it's "fine" but with a bit of additional strain it becomes apparent.


Its a duke, no timing chain, gears.

When they dont make much noise so they likely aren't stripped. Plus It would affect high RPM pulls the hardest. Once she clears her throat she pulls fine to 5k
82-T/A [At Work] FEB 09, 03:58 PM

quote
Originally posted by Dukesterpro:

Its a duke, no timing chain, gears.

When they dont make much noise so they likely aren't stripped. Plus It would affect high RPM pulls the hardest. Once she clears her throat she pulls fine to 5k




When you say misfire... is it bogging down, or are the plugs actually firing indiscriminately or out of order? You said you replaced the ignition control module, so I'm assuming it's a 1984-1986 and not an 87-88 w/ DIS ignition. So if you've replaced the ICM, and the TPS... and you've ensured that the TPS is properly adjusted... the only other thing that I can think of that would cause bogging down would be:

1 - Fuel issue from inconsistent fuel delivery... that could mean that it's providing "consistent" fuel, but when the demand for more fuel exists, it's starting to lean out. This can be either a clogged fuel filter, clogged fuel pick-up sock, or even a clogged or sticking injector in the TB.

2 - MAP Sensor: No idea how this thing works, but I've had several Fieros where they bogged hard... almost totally undriveable other than at idle, and I've had to disconnect or plug the MAP sensor for me to even be able to drive home (and bucking stops). Cheap fix in this case.

3 - Catalytic Converter: Yup... definitely been there, done that. I had a 1997 Pontiac Grand Am GT that I sold in 2006 because I couldn't figure out what was wrong with it. I replaced basically everything... timing chain, injectors, ignition packs, everything. Idled AMAZING... turns out... the catalytic converter (pre-cat) had completely melted because I used a can of SeaFoam and I guess it was just a bit too much for it. It ran very hot and melted the cat. The new owner of the car (whom I sold it to for $2,500) was kind enough to let me know what the problem ended up being, after I spend $3,000 in parts! It would idle... meaning I could move it around the cul-de-sac, but any significant throttle and it just bucked and sputtered and popped.


Hope that helps!
Dukesterpro FEB 09, 06:31 PM

quote
Originally posted by 82-T/A [At Work]:
When you say misfire... is it bogging down, or are the plugs actually firing indiscriminately or out of order? You said you replaced the ignition control module, so I'm assuming it's a 1984-1986 and not an 87-88 w/ DIS ignition. So if you've replaced the ICM, and the TPS... and you've ensured that the TPS is properly adjusted... the only other thing that I can think of that would cause bogging down would be:

1 - Fuel issue from inconsistent fuel delivery... that could mean that it's providing "consistent" fuel, but when the demand for more fuel exists, it's starting to lean out. This can be either a clogged fuel filter, clogged fuel pick-up sock, or even a clogged or sticking injector in the TB.

2 - MAP Sensor: No idea how this thing works, but I've had several Fieros where they bogged hard... almost totally undriveable other than at idle, and I've had to disconnect or plug the MAP sensor for me to even be able to drive home (and bucking stops). Cheap fix in this case.

3 - Catalytic Converter: Yup... definitely been there, done that. I had a 1997 Pontiac Grand Am GT that I sold in 2006 because I couldn't figure out what was wrong with it. I replaced basically everything... timing chain, injectors, ignition packs, everything. Idled AMAZING... turns out... the catalytic converter (pre-cat) had completely melted because I used a can of SeaFoam and I guess it was just a bit too much for it. It ran very hot and melted the cat. The new owner of the car (whom I sold it to for $2,500) was kind enough to let me know what the problem ended up being, after I spend $3,000 in parts! It would idle... meaning I could move it around the cul-de-sac, but any significant throttle and it just bucked and sputtered and popped.


Hope that helps!




Oh nuts.

It's starting to jog my memory that I was dumping seafoam into the motor during its first time being fixed since the lifter was starting to tick. I bet you I killed the cat. Will cut it out this weekend. Its rattling like a mofo anyway


The misfire is odd, it's like the engine is outrunning the spark. The ignition just feels behind. I doubt its fuel related. It has a brand-new pump and filter. Im going to post a youtube video]


Here's a youtube video of my car, the noise is faint, but Im holding the pedal right at the place it likes to misfire, its just about half throttle but its more based on engine load than throttle position. Meaning the place on the pedal it misfires changes based on the speed of the car.. You can hear it struggling https://www.youtube.com/shorts/O9Aw71vKrD4.

Im still concerned about the fact I cant get the idle to come down. I reset the computer and it idles pretty nicely at about 800 for 20 seconds and then climbs right up and I get some light to moderate greyish white smoke out the pipe
Patrick FEB 09, 08:10 PM

quote
Originally posted by Dukesterpro:

You can hear it struggling...




I can hear either a loose rod or severe pre-ignition (or maybe even a couple spark plug cables going to the wrong cylinders).

What have you got the ignition timing set to?

[This message has been edited by Patrick (edited 02-09-2023).]

82-T/A [At Work] FEB 09, 08:29 PM

quote
Originally posted by Dukesterpro:
Oh nuts.

It's starting to jog my memory that I was dumping seafoam into the motor during its first time being fixed since the lifter was starting to tick. I bet you I killed the cat. Will cut it out this weekend. Its rattling like a mofo anyway


The misfire is odd, it's like the engine is outrunning the spark. The ignition just feels behind. I doubt its fuel related. It has a brand-new pump and filter. Im going to post a youtube video]


Here's a youtube video of my car, the noise is faint, but Im holding the pedal right at the place it likes to misfire, its just about half throttle but its more based on engine load than throttle position. Meaning the place on the pedal it misfires changes based on the speed of the car.. You can hear it struggling https://www.youtube.com/shorts/O9Aw71vKrD4.

Im still concerned about the fact I cant get the idle to come down. I reset the computer and it idles pretty nicely at about 800 for 20 seconds and then climbs right up and I get some light to moderate greyish white smoke out the pipe




I'm definitely not saying it's a definite... but that is totally what happened to me... haha, and it totally killed my cat. I try to use it on a totally full tank, and not continuously.

White / greyish smoke usually means that you're burning oil, and that would normally be an indicator of worn O-rings; however, I think your problem could likely be more a PCV problem. It's been a long time since I've had a Duke, but there's a PCV valve somewhere that connects to the top of the crankcase to the air cleaner. I think it might be between where the air cleaner goes over the crankcase. It's a cheap part to replace, like 10 bucks or less.

But yeah, I hear a lot of pinging... which definitely means that the fuel is pre-detonating, which could simply mean that it's running really hot. With a huge vacuum leak, that certainly could be causing your problems too, AND... cause your cat to melt (due to running too lean).

Try not to drive it too much like this, because you can burn your valves and damage the valve seats if it's running too lean.

I'm trying to think of all the places that you could have a vacuum leak. So, of course you have the brake booster... just thinking out loud here. The brake booster uses vaccum to provide boost to the brakes. How do the brakes feel? It's possible that if you have a leak anywhere in the line, it could be causing it.

The Iron Duke is pretty simple... you basically have an intake manifold, a TBI unit, and everything plugs into the TBI unit. You COULD unplug literally every vacuum line, and then PLUG it closed on the intake manifold... and THEN see if your idle is still high.

If the idle is high at that point, then it's likely a problem with your IAC / Idle Air Control valve. I can't remember if you said you replaced that... but that unscrews and then you usually hit the hole with some carb cleaner, and also the IAC valve too. But if you are feeling lucky, just replace it if you haven't already. They don't last forever. If you still have a problem, then you may also need to adjust the arm on your TPS... especially if you just replaced it. They aren't always good from stock.

If after plugging all the holes in the intake (as in, after removing all the EGR lines and plugging them)... you don't have ANY high idle... then I'd simply go through the process of elimination by re-installing them one by one until the high idle comes back.

But to be clear, if you're hearing a rattling in your catalytic converter, it definitely means that the honeycomb broke up, and what can happen is that a large chunk of it gets lodged in the exit of the cat, sideways... which means it's blocking the hole... and it will continue to do that until you let off the pressure and it rattles again... hah...

Hopefully that helps.
Dukesterpro FEB 10, 01:53 AM

quote
Originally posted by Patrick:

I can hear either a loose rod or severe pre-ignition (or maybe even a couple spark plug cables going to the wrong cylinders).

What have you got the ignition timing set to?




Damn Patrick, you know your stuff.

The timing was initially set to something, who knows, I never checked since it had been working fine *facepalm*

I filled it up with 91 octane from empty to see if it would change, there was an immediate improvement. Drove it 20 miles home. Retarded the timing slightly with terminal A and B jumped and In the dark found a spark plug arching to the exhaust manifold. Fixed. No more stumble. However, Idle is still too high, and now I have some pretty clear pinging that starts under load at mid-throttle and seems to get better or sometimes disappear at wide open. I plugged every port except the map and still high idle and pinging. I think, here's another video for your expert ears https://www.youtube.com/shorts/E8PFNOhRaOk

I'm starting to think a new EGR might be the way forward. I read in another post here that mid throttle pinging and high idle is almost exclusively EGR related.

Once again, please advise.
Patrick FEB 10, 03:50 AM

quote
Originally posted by Dukesterpro:




Sounds to me like it's still pinging under load. You didn't say what you set the ignition timing to.

If you don't have a timing light, the ignition timing can be set "by ear". When driving up a slight incline in 4th gear at 30 mph, floor the accelerator. If the engine pings (as it's currently doing), retard the ignition a bit and do the driving test again. Keep doing this until the ping is eliminated, and then retard the ignition just a bit more. Keep in mind that if you've put 91 octane gas in the tank, you'll have to do this again with 87 octane fuel. And no, don't keep using 91 octane gas. It's a waste of money with an engine designed to run on 87 octane.

You also need to make sure the EGR valve is opening. With the car parked and running, stick a finger up through a hole in the underside of the EGR valve and see if the diaphragm moves when the throttle is opened. (If you have an aftermarket EGR valve, the holes may be too small for a finger. If so, I'll advise further.) Also check (when the engine's not running) to see if the diaphragm is airtight by pushing up on the diaphragm with the vacuum hose disconnected. Then put a different finger over the vacuum hole, release the diaphragm, and see if it holds until you take your finger off the vacuum hole.

[This message has been edited by Patrick (edited 02-10-2023).]

Dukesterpro FEB 10, 11:05 AM

quote
Originally posted by Patrick:

Sounds to me like it's still pinging under load. You didn't say what you set the ignition timing to.

If you don't have a timing light, the ignition timing can be set "by ear". When driving up a slight incline in 4th gear at 30 mph, floor the accelerator. If the engine pings (as it's currently doing), retard the ignition a bit and do the driving test again. Keep doing this until the ping is eliminated, and then retard the ignition just a bit more. Keep in mind that if you've put 91 octane gas in the tank, you'll have to do this again with 87 octane fuel. And no, don't keep using 91 octane gas. It's a waste of money with an engine designed to run on 87 octane.

You also need to make sure the EGR valve is opening. With the car parked and running, stick a finger up through a hole in the underside of the EGR valve and see if the diaphragm moves when the throttle is opened. (If you have an aftermarket EGR valve, the holes may be too small for a finger. If so, I'll advise further.) Also check (when the engine's not running) to see if the diaphragm is airtight by pushing up on the diaphragm with the vacuum hose disconnected. Then put a different finger over the vacuum hole, release the diaphragm, and see if it holds until you take your finger off the vacuum hole.





Ignition timing is unknown, I just backed it off a bit. I'm going to get a light soon. Until then I will use your method.

Not able to check the EGR right now as I am at work. But if it fails either of two tests, should I just replace it. I have a local new replacement here for 55 dollars. The one I have in there now is the factory original. Never been changed according to the previous two owners

Thanks

[This message has been edited by Dukesterpro (edited 02-10-2023).]