Scary Brief Engine Misfire

[BodybyFisher]

OK, I think its official, I am pretty sure I am at the beginning stages of needing head gaskets.

Ignition wires replaced, plugs replaced on 1, 3, 2 and 4 and I still have a brief misfire on 1. Hooking up my Autotap diagnostic scanner to the engine it shows a slight misfire on 1 and 3, again adjoining cylinders. There is no reason that I should have a misfire at this point

I think I am going to check for carbon by products at this point

[adallak]

OK, I think its official, I am pretty sure I am at the beginning stages of needing head gaskets.

Ignition wires replaced, plugs replaced on 1, 3, 2 and 4 and I still have a brief misfire on 1. Hooking up my Autotap diagnostic scanner to the engine it shows a slight misfire on 1 and 3, again adjoining cylinders. There is no reason that I should have a misfire at this point

I think I am going to check for carbon by products at this point

Mike, do not jump to conclusion. I have done pretty much everything you have done plus replaced all the injectors. Still have misfire and rough idle. The only thinh I have not replaced is the ECM.

[Cadillac Jim]

How about crossfiring between the cylinders? The layout of the wires is critical in preventing that. Also, there can be some interference in the injector wiring from the spark plug wires.

[BodybyFisher]

I started this morning and got the misfire again, just briefly. The ignition wires are new, I used loom on them to keep them apart, and where they cross metal, they do not travel side by side with any injector wires.

My next step is to check my injector resistence cold and warm to see if they are drifting

I think ill drop 4 cooling supplement tablets in to see if that moderates this mis.

The plugs on 2 and 4 were burned WHITE with some sort of build up on them, the electode was buried in white scale.

I am not sure if a compression test would indicate anything at this point. If this was coolant leaking into the cylinder, I should be overheating, as compression certainly would go the other way and superheat the coolant.

Any ideas as to what is causing this brief misfire?

[Jan Olsson]

I started this morning and got the misfire again, just briefly. The ignition wires are new, I used loom on them to keep them apart, and where they cross metal, they do not travel side by side with any injector wires.

My next step is to check my injector resistence cold and warm to see if they are drifting

I think ill drop 4 cooling supplement tablets in to see if that moderates this mis.

The plugs on 2 and 4 were burned WHITE with some sort of build up on them, the electode was buried in white scale.

I am not sure if a compression test would indicate anything at this point. If this was coolant leaking into the cylinder, I should be overheating, as compression certainly would go the other way and superheat the coolant.

Any ideas as to what is causing this brief misfire?

Have you checked the compression?

[BodybyFisher]

I started this morning and got the misfire again, just briefly. The ignition wires are new, I used loom on them to keep them apart, and where they cross metal, they do not travel side by side with any injector wires.

My next step is to check my injector resistence cold and warm to see if they are drifting

I think ill drop 4 cooling supplement tablets in to see if that moderates this mis.

The plugs on 2 and 4 were burned WHITE with some sort of build up on them, the electode was buried in white scale.

I am not sure if a compression test would indicate anything at this point. If this was coolant leaking into the cylinder, I should be overheating, as compression certainly would go the other way and superheat the coolant.

Any ideas as to what is causing this brief misfire?

Have you checked the compression?

Not yet Jan, I will, with this NS, I need a special compression tester to reach so deep. Ill begin getting deeper into this. I think a cooling system pressure test is next. There is definately something wrong however and this problem definately limits my trips this summer, I dont want to be in 100 degree heat and have a big problem

[Jan Olsson]

You mean with a pice of pipe (8" or so) at the end? I used one with a hose and a threaded brass end with an o-ring. It was quite easy to have the end locate the spark plug threads and pull just enough to let the o-ring seal.

[BodybyFisher]

You mean with a pice of pipe (8" or so) at the end? I used one with a hose and a threaded brass end with an o-ring. It was quite easy to have the end locate the spark plug threads and pull just enough to let the o-ring seal.

Thanks, I think JimD or Kevin has photos someplace of theirs, I need to make one,

[Cadillac Jim]

I would change the rest of the plugs before I did anything else except check the coolant for combustion products or do a coolant system pressure check.

[BodybyFisher]

I would change the rest of the plugs before I did anything else except check the coolant for combustion products or do a coolant system pressure check.

Good catch Jim, that is next on deck, but if in fact #1 and #3 are still misfiring, I dont think that will matter, but, maybe, what is happening is because the OTHER cylinder on the #1 and #3 coils might have bad plugs on them, increasing the resistance to fire, they are USING/KILLING the coils 'overhead' and causing a misfire when it comes back to fire #1 and #3, especially when cold... Funds are short, the other 4 plugs at $7 each are on next weeks budget

[JimD]

You mean with a pice of pipe (8" or so) at the end? I used one with a hose and a threaded brass end with an o-ring. It was quite easy to have the end locate the spark plug threads and pull just enough to let the o-ring seal.

Thanks, I think JimD or Kevin has photos someplace of theirs, I need to make one,

Mike:

My adapter is designed to thread into the plug hole and allow shop air to pressurize the combustion chamber. But it could be adapted to accept a compression guage.

I would be happy to loan it to you if you think it would be useful....

[BodybyFisher]

Thanks Jim, let me go home an look at my compression tester and see what I can make up, thanks for the offer

[KHE]

Here is a photo of the pressure adapter I made to test the head gaskets on my '97 STS. I used an old spark plug and ground off the metal ring at the porcelain and then drilled and tapped the center of the threaded portion for a 1/8" (I think) pipe thread. The tap drill size was very close to the ID of the threaded portion of the spark plug. I used red Loctite on the threads to make sure it wouldn't come apart.

[BodybyFisher]

Here is a photo of the pressure adapter I made to test the head gaskets on my '97 STS. I used an old spark plug and ground off the metal ring at the porcelain and then drilled and tapped the center of the threaded portion for a 1/8" (I think) pipe thread. The tap drill size was very close to the ID of the threaded portion of the spark plug. I used red Loctite on the threads to make sure it wouldn't come apart.

Thanks Kevin, that is the photo I was thinking of

[Jan Olsson]

I was thinking that since the car ran better after you changed the plugs but you still have a problem with the no 1 cylinder it seems like it is ignition related after all. But if you have good plugs/connections/cables there can only be a problem with the ICM or PCM (sounds unlikely) or with the fuel delivery (except from compression). Have you tried a pressure leak down test with the internal diagnostics? If you have OBD I that is?

[adallak]

I was thinking that since the car ran better after you changed the plugs but you still have a problem with the no 1 cylinder it seems like it is ignition related after all. But if you have good plugs/connections/cables there can only be a problem with the ICM or PCM (sounds unlikely) or with the fuel delivery (except from compression). Have you tried a pressure leak down test with the internal diagnostics? If you have OBD I that is?

Even removing and reinstalling PCM and PROM may help to improve connections. Replacing PCM with a reman. unit is not a big deal either. But something makes us to skip easy steps and prepare for the worst. Do you think I have touched my ECM to isolate misfire? Nope.

[Jan Olsson]

I was thinking that since the car ran better after you changed the plugs but you still have a problem with the no 1 cylinder it seems like it is ignition related after all. But if you have good plugs/connections/cables there can only be a problem with the ICM or PCM (sounds unlikely) or with the fuel delivery (except from compression). Have you tried a pressure leak down test with the internal diagnostics? If you have OBD I that is?

Even removing and reinstalling PCM and PROM may help to improve connections. Replacing PCM with a reman. unit is not a big deal either. But something makes us to skip easy steps and prepare for the worst. Do you think I have touched my ECM to isolate misfire? Nope.

Go on. Touch it As a matter of fact I have my PCM right besides me at the desk. I like to keep it safe

Actually I had to pull it in order to replace my radiator.

[Texas Jim]

I was thinking that since the car ran better after you changed the plugs but you still have a problem with the no 1 cylinder it seems like it is ignition related after all. But if you have good plugs/connections/cables there can only be a problem with the ICM or PCM (sounds unlikely) or with the fuel delivery (except from compression). Have you tried a pressure leak down test with the internal diagnostics? If you have OBD I that is?

Even removing and reinstalling PCM and PROM may help to improve connections. Replacing PCM with a reman. unit is not a big deal either. But something makes us to skip easy steps and prepare for the worst. Do you think I have touched my ECM to isolate misfire? Nope.

Go on. Touch it As a matter of fact I have my PCM right besides me at the desk. I like to keep it safe

Actually I had to pull it in order to replace my radiator.

I have my ECM (engine control module) and TCM (transmission control module) in my roll-a-way toolbox.

Locked up for safe keeping.

[navion]

Mike,

As this thread started a while back, I can't remember if I responded to it before or not.

I had a similar misfire problem with my 94 SLS that drove me nuts.

I changed plugs and wires, I removed the manifold & cleaned out the EGR passages, replaced the fuel pump fuel pressure regulator and a few other things that I have probably forgotten.

In desperation, I even took it to the local Caddy dealer who said that I had a hole in the plenum! (It didn't!)

I even quit driving the car for a while.

Finally I asked an ex-Caddy mechanic to take a look at it. He found that there were a couple of HI-tension connections on one of the coils that was corroded. He cleaned the contacts and the problem disappeared!

I haven't had much time to get on the computer lately and don't know if this aspect has already been discussed or not. I hope that it helps.

Take Care,

Britt

[BodybyFisher]

OK replaced all of the plugs now.

It still is rough now, I say rough because its not setting a code for a MISFIRE but its rough on start up but only for about a minute. With the new plugs, wires, egr cleaning, coil cleaning and TB cleaning the engine is very powerful and smooth.

I did a test, however

If I floor it twice on start up, the ROUGHNESS goes away and the engine is smooth, after I do that, I have a strong FUEL smell as I back out of my driveway.

My theory is that I have a leaky injector or two

I plan to lift my injector rail, support it in the air and pressurized the fuel system (turn the key on) and look for dripping, its possible that on shut down a leaky injector is emptying the fuel rail pressure into the cylinder. This could be a couple of dirty injectors

Any thoughts?

I guess, I could check my digital vs. actual calculated fuel mileage for a test PLUS, I would imagine that if I sent my OIL in for analysis, I would have fuel in it

Any thoughts?

[Cadillac Jim]

Well, the obvious one is the FPR but I'm sure that you eliminated that long ago. A leaking injector shouldn't cause rough idling on cold starts for the same reason that a diaphragm leak in an FPR doesn't usually cause problems in cold starts. You've also eliminated manifold leaks, EGR valve and plumbing, EVAP system (I think), plugs, wires, and coils, and crank sensors. If you haven't eliminated a leak in the EVAP purge valve or a problem in its operation, this is the time. Also, the EVAP system may be saturated; sometimes not driving at a steady speed so the EVAP system can purge can happen when cars are driven in urban environments without a freeway break every week or so.

Your original complaint was rough idle after an Italian tune-up; this is common in cars that don't see highway driving very much and is basically loosened carbon deposits. That should have all gone away by now, but a 50-mile trip should clear that up if it's the problem -- and it should provide the EVAP system a good chance to purge.

Since you've seen codes on #1 and #3 and you've seen all the plugs, then you know to look at cylinders #1, #3, and any among the rest whose plug looked different from the others. That probably won't tell you about a leaking injector because running closed loop will make the cylinder run OK.

Pressing the accelerator during starting shouldn't do anything with DFI. Since it does result in unburnt fuel that you can smell when backing up, I would look at that in the FSM; all mine says is that pressing the accelerator to the floor while turning the engine with the starter turns off the fuel.

Things that do occur to me are the ECT sensor and the IAT sensor, or a FPR that allows very high or very low fuel pressure at startup or is sticky, or a dying fuel pump, or an error in the output of the TPS; these are things that can force a bad mixture at start-up.

Other possibilities that may cause the engine to run rich or lean on initial start-up include the MAF and MAP sensors, but I'm not sure what these do to the mixture in open loop mode.

Have you tried smelling the oil dipstick? Your nose can be almost as sensitive as an oil analysis for gasoline.

Failing all else, I would drive it for a week and look at the plugs again.

[adallak]

My theory is that I have a leaky injector or two

I plan to lift my injector rail, support it in the air and pressurized the fuel system (turn the key on) and look for dripping, its possible that on shut down my in leaky injector is emptying the fuel rail pressure into the cylinder. This could be a couple of dirty injectors

Though lifting the fuel rails is not a big deal, you can check your theory simply by releasing the fuel pressure via shredder valve as soon as you finish the driving for the day. If that eliminates the symptoms, you can lift the fuel rail to see which one is leaking.

[Cadillac Jim]

My theory is that I have a leaky injector or two

I plan to lift my injector rail, support it in the air and pressurized the fuel system (turn the key on) and look for dripping, its possible that on shut down my in leaky injector is emptying the fuel rail pressure into the cylinder. This could be a couple of dirty injectors

Though lifting the fuel rails is not a big deal, you can check your theory simply by releasing the fuel pressure via shredder valve as soon as you finish the driving for the day. If that eliminates the symptoms, you can lift the fuel rail to see which one is leaking.

For those of you who aren't BodybyFisher, Ranger, or other experienced mechanic, be sure and have a paper (not polystyrene) cup and/or shop rag ready to catch the gasoline when you open the Shrader valve. Having a fire extinguisher handy might be a good idea too.

[BodybyFisher]

My theory is that I have a leaky injector or two

I plan to lift my injector rail, support it in the air and pressurized the fuel system (turn the key on) and look for dripping, its possible that on shut down my in leaky injector is emptying the fuel rail pressure into the cylinder. This could be a couple of dirty injectors

Though lifting the fuel rails is not a big deal, you can check your theory simply by releasing the fuel pressure via shredder valve as soon as you finish the driving for the day. If that eliminates the symptoms, you can lift the fuel rail to see which one is leaking.

For those of you who aren't BodybyFisher, Ranger, or other experienced mechanic, be sure and have a paper (not polystyrene) cup and/or shop rag ready to catch the gasoline when you open the Shrader valve. Having a fire extinguisher handy might be a good idea too.

That's a good and easy idea Adallak, I think Ill try that. I have to think that is what is happening, I am getting extended cranking, so its possible that the pressure is bleeding off. I have a fuel pressure gage, that has a pressure relief button and a hose that vents pressurized fuel, which I usually put into a coffee can (not styrofoam cup lol). I am smelling fuel, so I am thinking that I am honing in on the problem

Jim, yes, I did replace my FPR about two years, ago, my old one is fine and sitting on my workbench, maybe Ill swap it in and see what happens.

[BodybyFisher]

OK did a couple of tests

Attached a vacuum gage on the intake vacuum port that attaches to the T that goes to the HVAC/Brake/Vacuum tank (before the check valve), at idle my vacuum holds steady at 16 HG. This is an old gage, and 'normal' is 20, but that is for normally aspirated OHV engines, not sure what the vacuum (hg) should be on a 32 valve NS, anyone know?

Then I attached a fuel pressure gage, I get 42 PSI at idle, when I turn the key off, it holds at 40 PSI. I watched for 5 min and it held 40 PSI. Will wait for it to cool (when problem occurs) and see what I have

By the way, when I pull the vacuum hose off of the FPR, my fuel pressure increases to 45 PSI, and I do not get any fuel out of the vacuum port of the FPR