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Looking for Ideas - Detonation in Exhaust

4K views 34 replies 6 participants last post by  MaddMartigan 
#1 ·
OK, if you've followed my Project Resurrection thread, you've seen my issues with the engine. I'm at a loss so I figured I would start a thread in this forum to start figuring out how to troubleshoot the issue.

I'll try to create a video with the audio of what's going on but I don't have that just yet. I'll post it when I have it.

Long story short, all signs point to detonation in the exhaust. It does this almost immediately after starting the car. I say detonation in the exhaust because I had a buddy check it out with me and he indicated that it was detonation in the exhaust.

Here is a short list of what I've checked/changed:
  • Ignition System
  • Timing
  • Fuel Pressure
  • Vacuum Leaks (as best as I could)
  • Exhaust Leaks
  • Pulled Codes (No codes)
  • Re-flashed Chip
  • Wiring

I'm open to any other ideas.
 
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#2 ·
Detonation in the exhaust Immediately after Starting it would have to mean at least one cylinder is firing with an exhaust valve open, and unburned fuel is in the exhaust.

If it does it after the exhaust is hot, then it can be too much fuel, maybe a stuck injector.



Can you tell if it's one cylinder, on both sides, or randomly in both sides?

Adding a meter across an injector, and shining the timing light hooked to that cylinder could show this; the injector has to fire, then the spark, and the crank needs to be in the right spot.
If you can get an led across the injector and shine it on the crank wheel, you could see how many degrees apart they are, and where it's timing.
Search this: MSD Ignition Timing Tapes for Harmonic Balancers
These are tapes that stick to the harmonic balancer, and show the timing.

A boom in the exhaust is going to be after TDC; it should be before. Max on my car is set to about 20 degrees before, iirc.

A consistent ignition in the exhaust is going to be the timing is off, somehow.

A random firing is going to probably be noise pickup in the sensor wiring; or maybe a bad pickup in the distributor. (maybe a spark plug wire is too close to a sensor wire, or a spark leak in the distributor?)
Spark leaking in the distributor should leave a track, a darkened area like a line drawn with a pencil.
If the cap is dirty, you can wash it out with rubbing alcohol, or starting fluid.

One side only could be a stuck valve, and it's open when the cylinder fires. But where's the gas coming from, if there's no timing problem?
And you usually hear valve problems, when the piston smacks it.

That's everything I can think of; I hope it helps. :)
 
#3 ·
Detonation in the exhaust Immediately after Starting it would have to mean at least one cylinder is firing with an exhaust valve open, and unburned fuel is in the exhaust.
While I agree with this in principle, it also doesn't make sense when I think about it. I'll try to get a video/audio of it.

If it does it after the exhaust is hot, then it can be too much fuel, maybe a stuck injector.
The car has never had a chance to get hot. I have replaced all of the injectors with new ones. I don't think this is it.

Can you tell if it's one cylinder, on both sides, or randomly in both sides?
It is totally random. It sounds like it's all sides but I've been afraid to run it too long to find out for sure.

Adding a meter across an injector, and shining the timing light hooked to that cylinder could show this; the injector has to fire, then the spark, and the crank needs to be in the right spot.
If you can get an led across the injector and shine it on the crank wheel, you could see how many degrees apart they are, and where it's timing.
Search this: MSD Ignition Timing Tapes for Harmonic Balancers
These are tapes that stick to the harmonic balancer, and show the timing.
I have a balancer that has timing marks on it. I have manually set the timing and ensured it's right by using my compression tester and hand cranking the engine until I'm getting compression on #1 and it aligns to the 10 degrees BTDC and then installing the distributor per standard practice. I have run the car long enough to then use the timing light (with SPOUT removed) and set the timing at run to 10 degrees BTDC. The timing is correct for sure.

A boom in the exhaust is going to be after TDC; it should be before. Max on my car is set to about 20 degrees before, iirc.
A consistent ignition in the exhaust is going to be the timing is off, somehow.
See timing comment above.

A random firing is going to probably be noise pickup in the sensor wiring; or maybe a bad pickup in the distributor. (maybe a spark plug wire is too close to a sensor wire, or a spark leak in the distributor?)
Spark leaking in the distributor should leave a track, a darkened area like a line drawn with a pencil.
If the cap is dirty, you can wash it out with rubbing alcohol, or starting fluid.
I've been worried that this is a thing. I have swapped distributors without any change. I have re-routed the wires because I thought that maybe that was the issue but it showed nothing. I pursued the shielded wire stuff and it's all shielded and nowhere near the alternator. I have checked the cap repeatedly and there is nothing strange inside it. No odd marks, no extra dirt/dust. Just looks normal. I still feel like this is a thing however.

One side only could be a stuck valve, and it's open when the cylinder fires. But where's the gas coming from, if there's no timing problem?
And you usually hear valve problems, when the piston smacks it.
It feels like if I had a stuck valve that I would experience something more consistent. When I had a buddy listen to the car in person his assessment was that the car is running normally other than the loud pops. He's built several engines that actually run and have run for years so I trust him. He's actually the guy that got me into all of this almost 20 years ago.

That's everything I can think of; I hope it helps. :)
That does help. If nothing else it helps my sanity.

I have to admit one thing. I dreamed of it all night last night. The vacuum hose for the PCV valve to the upper intake ports is the original for the car. It's rather firm but I haven't replaced it because it's a molded hose and there is no aftermarket replacement. It's also the biggest diameter vacuum hose. If it's sucking air then it could be significant. I'll work to change that this evening but since I've tried so many other things without success I'm not getting my hopes up on this one either.
 
#4 ·
Silly question, but you did change out the eec at some point, I think, right?

If you're using a chip, can you try it without it without blowing anything up?

Dang; this is too good a project for something random like this. :(

I just had to throw everything out there; I'm betting when you find it, it will be something easy; that's the way it seems to go with me, anyway.

Keep your chin up; we'll find it. :)

We need Matt; he's the Genius. :D
I'm more the village idiot, on a good day, lol.
 
#5 ·
I have also swapped the ECM with no success. I could pull the chip but it would resort to running off the stock tables for 19lb. injectors and the stock MAF. It would then be super rich and I would expect the problem to be worse.
 
#6 ·
I agree it would not be optimal, but at idle it might be close enough to run, and I'm just curious if it still fires in the exhaust.

I certainly wouldn't want to blip the throttle hard; it will be ~20-30% lean, but it doesn't take a bunch of gas to idle.

It will probably act like it's starving for gas, but the lack of the 'boom' would tell you a lot.

I'm just wondering if there's a way to eliminate the piggyback chip as a source for this.

EEPROM chips have been known to toggle bits when they get old. (That's why they put tape over the window on the older ones, UV light from florescent lights would erase them sitting on the bench. I've had that happen at work, years ago; that's hard to find, lol)

I'm sure you've cleaned the pins carefully, and all that stuff; but when I get wrong results, flashing back to the stock program to see if it runs is my first step.
In my case, it's usually my fault, lol.

I'm just trying to cover everything; like I said before, when you find it, it will be something easy we haven't thought of yet.

It ran perfect before the wreck; and it's really close, just with some unwanted 'features'. :)
 
#7 ·
OK, more work. I did swap chips. At first I thought I fixed it but the more I observe it, the more I know that it's a problem that only exists at idle. If I give it some gas then it clears up. I'm beginning to wonder if I have a stuck injector or something. I'm also wondering if the base tables are just too rich and it's causing it because it seemed like it improved once it started to warm up a bit. I'm still confused but it's better than I was feeling. :confused::confused::confused:

Video with burned chip:
https://youtu.be/p7WRoPUXuzc

Video with Quarterhorse:
https://youtu.be/qN0HVJdAaVc

I apologize in advance for the shitty audio. Apparently my phone doesn't handle that noise all that well. You'll still get the picture of what it's doing though.
 
#8 ·
I've heard that before; that's what my 750 does when the carbs need cleaning, and are dribbling gas down the pipes.

I think you're on the right track; rich, or stuck injector.

That does not sound like it's in the manifold, but lower down.

I'm guessing there's no restriction in the exhaust, so it whooshes rather than bangs. :)

Are you sure there's not a puddle of gas in the pipes?

The normal firing will blow it out, then it will pop again as air gets scavenged back into the pipe.

It's rich burning (lots of fuel to the air, when it whooshes), otherwise the pipes would ring. :)

The QH video seems to do it less; can you compare the tables?
 
#9 ·
So, it's either too much fuel or unmetered air. I feel better about it now. Matt mentioned that he thinks it's unmetered air. I have two things to check. One is the thermactor ports on the back of the heads. The other is the connection at the collectors. When the engine was pulled and on a stand the plugs on the thermactor ports could have loosened. The collectors have been a deteriorating connection for a while because of all of the removals. I'll work on those first.

The too much fuel thing seems less likely but I can roll back to the old injectors and see if that helps if the air fixes don't.
 
#13 ·
I had a burned chip in the car. I do generally have it resolved now.

I'm just in hell getting the clutch to work. I can get the throwout bearing to move about 1/2 inch which either apparently isn't enough to get the clutch to disengage or something else is wrong.

I don't want to have to remove the transmission but that may be where I am.
 
#18 ·
The clutch only has to move 1/4" to let go; it needs to compress the springs, and clear the surface.

You're moving 1/2"; that should be way clear.

You're going to have to look.

Are you SURE it's moving that far?

If it's not, I could see it; but at that level of travel, you should have nothing.
 
#21 ·
OK, so the effort to do a reverse bleed didn't help. There is definitely something binding because the wheels don't really want to turn even with the car in neutral. I guess I'm pulling the transmission back out.

The bright side is that I can fix the collectors. :crying:
 
#22 ·
On the good side, maybe the clutch/linkage is all ok.

Rebuilding those isn't too bad (manuals in general); I'd bet it's in the shift forks, like Matt had to redo.

If they're bent, you can be in two gears at the same time; I've had a bike do that.

It's better in a car; you don't crash instantly. :thumbsup:

Are there two levers on the tranny linkage?
I remember an old chevy work van that the linkage would get jacked, external to the tranny, and you could crawl out in the middle of the intersection and jam it back into place with a big screwdriver. :facepalm: (god, I hated that van; they would Not replace it.)

It hit like 2nd and third, going to second, or some such.

What I'm getting at is that it might be a linkage problem, and that might be fixable externally.
One fork moves, one doesn't.

Have you tried moving the rear wheels backwards, while someone jacks the linkage/shifter? That was also a thing.
If it suddenly frees up, you know what to looks for, for sure, before you pull it.

For the record, I know nothing about these particular transmissions.
 
#23 ·
To my knowledge every thing is internal on these transmission. The car seems to shift just fine, it just won't disengage the clutch. Something is binding up and I'll need to separate the transmission from the engine to see what's up.
 
#27 ·
I keep thinking of your thread, with the external slave. D'oh!

Seems like Vic made one too.

My bad.

The only difference I see between S4gunn's setup and this guy is the Fidanza flywheel, and the side impact. :(
 
#29 ·
OK, lots of replies.

You've all nailed it in general. The transmission was in working order after the wreck since I drove it from the track to the tow truck. I also pulled it into the garage and out a few times.

The throwout bearing is definitely moving about 1/2" when pressing the clutch and I have verified that through the inspection window.

I'll just take it apart and see what I see.
 
#30 ·
Which parts are new, Just the flywheel and physical clutch plates/cover?

Do you still have the old parts? That gives you something to compare to.

One of the threads I saw elsewhere said something about the pilot bushing being the wrong size; I doubt you changed it, iirc it's in the crank.


I might try one more thing (I'm nuts...); since the slave is above the master, there could be a bubble in there.

If you REALLY want to know before you take it apart, you could hit the slave with the compressor to see if it will release.

If it's an air bubble, 150psi should still operate the throwout, unless you put a monster spring in it, or it's mechanically stuck.

It Will have an air bubble after that, so it still has to come out; but you'd know what it is.

It might blow the seals out of the slave, so there's that issue; I don't think so, but it's possible.

I test auto clutches with air, is why I even suggest it.
Nothing like building an auto clutch, and finding out a lip is curled over inside; I did that on the first one.


If you have one of the handheld brake "power bleeders", you could use that, and not really risk getting an air bubble in there.
 
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#31 ·
Good news. I pulled the transmission and the problem was the bolts that I used. The shoulder on the bolt was too long which didn't allow the pressure plate to evenly seat. I put on thick washers and the problem is solved. The car is back together and I've verified that everything is working as it should.
 
#34 ·
Nothing sucks more than to have everything together and you have to pull the trans or lift the engine out just to fix some issue like dropping something or the oil shaft into the oil pan. I've had to do that... twice. :)
 
#33 ·
Let's see that fire eating dragon make some smoke.
 
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