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Warm-start misfire


BostonETC97

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The past month or so, I've been having a misfire that only occurs upon a warm start, usually a couple hours after the car has been driven. She fires right up, but there's a definite miss at initial idle, and a very pronounced "buck" when backing out of a parking-space. The odd part... this misfire completely resolves itself within 30-45 seconds. By the time I have the car in 'drive' and pull away from a parking-space, she runs perfect. Almost reminds me of the misfire I had before the headgasket went, but that only happened on the first cold-start, and never again during the day.

No codes are set. New delco plugs and wires last year (~8,000 miles ago). I checked all the plug wires, and even re-set all the terminals on the ignition module. There doesn't appear to be any vacuum leaks, and otherwise runs great. The only other observation I have made is that there is a mild raw-fuel odor from under the hood, after the car has been driven and allowed to cool. I can't find a fuel leak, or signs of a leak anywhere, and the car has the new fuel-rail. Could this be a sign of a faulty injector, that's leaking into the intake after shutdown?

Thanks for the help!

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The past month or so, I've been having a misfire that only occurs upon a warm start, usually a couple hours after the car has been driven. She fires right up, but there's a definite miss at initial idle, and a very pronounced "buck" when backing out of a parking-space. The odd part... this misfire completely resolves itself within 30-45 seconds. By the time I have the car in 'drive' and pull away from a parking-space, she runs perfect. Almost reminds me of the misfire I had before the headgasket went, but that only happened on the first cold-start, and never again during the day.

No codes are set. New delco plugs and wires last year (~8,000 miles ago). I checked all the plug wires, and even re-set all the terminals on the ignition module. There doesn't appear to be any vacuum leaks, and otherwise runs great. The only other observation I have made is that there is a mild raw-fuel odor from under the hood, after the car has been driven and allowed to cool. I can't find a fuel leak, or signs of a leak anywhere, and the car has the new fuel-rail. Could this be a sign of a faulty injector, that's leaking into the intake after shutdown?

Thanks for the help!

Bad FPR (fuel pressure regulator)? Leaking injectors?

Pull the vacuum line off the FPR with engine running and see if there is any presence of gas in the hose or dripping from the FPR. There should be none.

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It shure sounds like an FPR to me. Addilac's check for gas at the vacuum line on the FPR should tell the tale.

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Pulled the vacuum hose off the FPR at idle. No fuel leaking out. I replaced the FPR about 5 years ago, but I suppose it could still be suspect. I should add that to my next RockAuto order! :unsure:

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Consider lifting the fuel rail, pressurizing it, and seeing if any injectors are leaky

Try pulling the vacuum hose off of the fuel pressure regulator and starting the engine, hold a white card up to the FPR nipple, race the engine a few times and see if it spits fuel

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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No spitting from the nipple! (That doesn't sound right, but hey, I said it!)

Sounds like the next step is to lift the rail and see who's leaking. What's the typical life-span of an injector? Am I looking at replacing all 8 (ouch!), or can I get away with only swapping out the faulty injector(s)?

I think I'll let this be a job for my mechanic. I just don't trust myself playing with a pressurized fuel system, and I don't want to create a giant Eldorado BBQ!

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I think you should eliminate a bad FPR first its the cheapest and easiest thing to do, 5 years old

Tighten grounds near the coils, and clean each coils tower and check for a good clean plug wire connection at each tower

Put a fuel pressure gage on your fuel rail and check your fuel pressure cold, hot, idling, and when it does the miss..

Do you smell fuel ever?

Don't rush to check the injectors yet, you could do it yourself its not hard to do, not much could go wrong if you are careful. In addition, when you reinstall the rail, you can replace the orings and make sure they are seated

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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No spitting from the nipple! (That doesn't sound right, but hey, I said it!)

Sounds like the next step is to lift the rail and see who's leaking. What's the typical life-span of an injector? Am I looking at replacing all 8 (ouch!), or can I get away with only swapping out the faulty injector(s)?

I think I'll let this be a job for my mechanic. I just don't trust myself playing with a pressurized fuel system, and I don't want to create a giant Eldorado BBQ!

If you do not have a fuel gauge, I can ship one to you free. I have got extra. Sealed, USA made. It also lets you to relieve the pressure safely.

The saddest thing in life is wasted talent

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nice adallak!

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thank you very much for the offer of the fuel gauge - I really appreciate it! The car is due for an oil service, and my local mechanic is a very reasonable and knowledgeable guy, so I think I'll let him lift the rail and check the injectors. While I do have the mechanical ability to do it, there are some jobs I'd rather leave to somebody with more experience. The $100 he'll charge me for the labor will be cheaper than the $800 I'll cost myself when I somehow manage to destroy all 8 injectors in the removal process! :P

Tonight when I started her up after a 4 hour "cool" down, the misfire was present. I took a good "whiff" of the exhaust, which had a very strong unburned-fuel aroma. By the time I got back into the car and put it in gear, misfire was gone, and she drove beautifully. I'm really starting to think it's a leaking injector. When my FPR failed the first time, I recall the car being very difficult to start. I'm not having any trouble with the starting, only the mild and short-lived misfire on a warmish engine.

I guess it sort of makes sense that on a hot-start there's no problem, as the injector either hasn't had time to leak, or the fuel vaporizes quickly. On a cold-start, the fuel that leaked out also has time to evaporate or leak past the piston rings. I'm thinking about this TOO hard... :huh:

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Another way to check this is the have your oil analyzed at Blackstone Labs

http://www.blackstone-labs.com/

They will tell you if you have fuel in your oil

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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As a "here goes nothing" attempt to correct the miss, I added Marvel Mystery Oil to my last tank of fuel, and mysteriously, the misfire is gone. My guess is that it's a short-lived fix, but I'll try to keep the glass half-full and see how it holds!

Perhaps a stuck/sticky/blocked injector that the MMO cleaned-up? I never really believed in additives, but Marvel seems harmless. I'll keep everybody posted how it works out!

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I know you got the miss to go away, but I'm gonna throw this out there as a suggestion anyhow. If your miss comes back, check your coil packs. I have had 3 out of the 4 of mine die out on me in the last 3 months, and the last 2 had the same symptoms you are describing for about 2-3 weeks before they totally crapped out. I had a miss on warm starts and an AWFUL raw gas smell from my exhaust. I actually ended up having to replace my cat converter as a result of the first one going bad. I didn't know what it was that was causing the problem, and my cat ended up cracking and clogging.

There are 2 ways I know of to check a coil pack (I'm sure there are others), both of which could be hard to determine results from because your miss doesn't last very long. The first is to swap each one out, one at a time, with a KNOWN good coil until the misfire goes away. The second, which is the method I have used to determine all 3 of mine that died, is a plug-boot check. Wear a heavy glove...something that is non-conductive, for safety reasons. Then with the car running, pull each of the plug boots on the front bank off the plug JUST SLIGHTLY and listen for the "tick tick tick" sound of the spark. If there is no sound, there is no spark. One of them could also be much quieter/weaker than the rest. Either case indicates a bad coil...or a bad wire, but since yours are new that is much less likely. If you can get to the boots on the rear bank, you could check those too, but odds are if you have a bad coil, both cylinders that it runs will be out of spark. I don't know why the MMO made your miss go away, but there's a chance it MAY come back the next time you fill your tank.

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As a "here goes nothing" attempt to correct the miss, I added Marvel Mystery Oil to my last tank of fuel, and mysteriously, the misfire is gone. My guess is that it's a short-lived fix, but I'll try to keep the glass half-full and see how it holds!

Perhaps a stuck/sticky/blocked injector that the MMO cleaned-up? I never really believed in additives, but Marvel seems harmless. I'll keep everybody posted how it works out!

Maybe you had a dirty injector, this is from the MMO web page, if that was the case Techron probably would have helped.

• Marvel reduces and prevents varnish and gum build-up, two key contributors to robbing engine performance. When you shut off your engine, a miniscule drop of fuel is left at the tip of the fuel injectors or carburetor jets. This miniscule drop off of fuel then solidifies into a varnish type residue. Over time, the accumulated varnish blocks the openings of the injectors or jets, contributing to lower performance and fuel economy and shorter life of these components.• Spark plug life is also extended by using Marvel in your fuel. It creates a cleaner burning cylinder environment that reduces carbon build-up on spark plugs resulting in better firing plugs that increase performance and durability

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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