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Old 10-18-2009, 05:18 PM   #1
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Default So, it idles on 3 cylinders - why?

This actually started quite some months ago and I never bothered to look into it. This is one of my winter projects and I'm looking for input.

Car starts and idles on 3 cylinders. Cold worse than hot, but still. I noticed this due to shaking engine and less vacuum.

Seems back to normal above 3000rpm-ish. Power is there: 235rwhp.

Cylinder 3 is not doing much. I can pull the plug wire and it idles the same. Not so on other cylinders.

Swapped injector, same.

Swapped coil between 2 & 3 (same pack), same.

Plug wire sparks violently on block if I let it. Less on other plugs actually so plenty of spark.

So - what are the options we have left?
- faulty or leaking HLA
- ?

I will have compression and leak down tested soon, but want ideas now.
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Old 10-18-2009, 05:39 PM   #2
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how's the no. 3 plug itself looking?
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Old 10-18-2009, 05:41 PM   #3
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how's the no. 3 plug itself looking?
Fine, like all the others. Swapped for new - same result.
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Old 10-18-2009, 05:43 PM   #4
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marginal injector that wont open below a certain pulsewidth?
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Old 10-18-2009, 05:45 PM   #5
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marginal injector that wont open below a certain pulsewidth?
No:
Quote:
Swapped injector, same.
I swapped injector 3 and 4. Still 3 is missing the show.
These are new flow tested RC 550s from BEGI.
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Old 10-18-2009, 05:49 PM   #6
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Quote:
Originally Posted by Spookyfish View Post
No:
I swapped injector 3 and 4. Still 3 is missing the show.
These are new flow tested RC 550s from BEGI.
Cylinder 3 is just lazy, only possible explanation.

I say look into the valvetrin, really the only other thing left since you have ruled out fuel and spark. Probably pointless even if you haven't already done it BUT..try swapping plug wires..? Good luck.

EDIT: nothing wrong with the injector's harness (car side not injector side) on #3 is there?
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Old 10-18-2009, 07:54 PM   #7
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cylinder health?
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Old 10-18-2009, 08:31 PM   #8
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Quote:
Originally Posted by Spookyfish View Post
I will have compression and leak down tested soon, but want ideas now.
Quote:
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cylinder health?
.
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Old 10-19-2009, 02:48 AM   #9
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I say look into the valvetrin, really the only other thing left since you have ruled out fuel and spark.
Another vote for valvetrain... ok

Quote:
Probably pointless even if you haven't already done it BUT..try swapping plug wires..? Good luck.
Wires swapped, no difference.

Quote:
EDIT: nothing wrong with the injector's harness (car side not injector side) on #3 is there?
The car is supposedly running fine in the higher rpm range, so, could it? Also I run MSPNP so the entire harness is OEM, nothing ever changes there. I doubt this is it.
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Old 10-19-2009, 04:05 AM   #10
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Quote:
Originally Posted by Spookyfish View Post
The car is supposedly running fine in the higher rpm range, so, could it? Also I run MSPNP so the entire harness is OEM, nothing ever changes there. I doubt this is it.
Probably not, but you never know, could be a fray in a wire or something and when the engine is at higher rpms it makes better contact **shrug** w/o testing the valve train that's the only thing left that comes to mind
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Old 10-19-2009, 04:08 AM   #11
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Quote:
Originally Posted by KPLAFIN View Post
Probably not, but you never know, could be a fray in a wire or something and when the engine is at higher rpms it makes better contact **shrug** w/o testing the valve train that's the only thing left that comes to mind
Does spraying unburned fuel out of the exhaust when cold rule this out?
It seems injection is happening, spark is there but no compression under 3krpm.
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Old 10-19-2009, 04:12 AM   #12
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cylinder health?
I doubt it's the block itself as it's still putting down 235rwhp on a stock 94 head. But I will have that checked.
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Old 10-19-2009, 01:47 PM   #13
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I think you've got your problem all but figured out, get those compression/leak down #'s and you'll have your answer.
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Old 10-19-2009, 01:52 PM   #14
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I still made 230rwhp as I blew my motor on the dyno itself. Ever since May I had smoke in boost and bad blow by. I had good compression across the board but horrible consumption. When I finally swapped the shortblock I only drained 3/4qt of oil, maybe 300 miles on it since the last change. lolz.
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Old 10-19-2009, 01:58 PM   #15
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I still made 230rwhp as I blew my motor on the dyno itself. Ever since May I had smoke in boost and bad blow by. I had good compression across the board but horrible consumption. When I finally swapped the shortblock I only drained 3/4qt of oil, maybe 300 miles on it since the last change. lolz.
Oil consumption on track is minimal. No smoke. I don't need your drama in my thread . Go scare someone else You had a stock engine. Also, 235rwhp is on a Superflow, not DynoJet.
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Old 11-09-2009, 05:27 AM   #16
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Hot leakdown ~80% in cyl #3 through valves.
Others are ~2%.
Ripping open valve cover this weak. Probably HLA.
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Old 11-09-2009, 07:46 AM   #17
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had the same problem in cyl 3 awhile back - runs like crap until you get above 2000 or 2500 rpm, then normal - water was getting past my headgasket (ouch)
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Old 11-09-2009, 07:58 AM   #18
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had the same problem in cyl 3 awhile back - runs like crap until you get above 2000 or 2500 rpm, then normal - water was getting past my headgasket (ouch)
That could also be the case as I did have cooling issues before...
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Old 11-09-2009, 09:58 AM   #19
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Intake valves are 'sagged'. Pulling head to see what's up (valve seats or?).
Probable cause is the overheating issues I had in the early days.
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Old 11-09-2009, 10:55 AM   #20
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perfect opportunity to source a '99 head though...
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