#1 cylinder seems to miss intermittanly

[ChevyBobby]

I'm missing something or I forgotten. I have a 1999 Siverado with a 5.7 vortec 350 with 160,000 miles on it. What it is doing is it has an interrmittent miss and it seems it is #1 cylinder because I pulled the plug wires one at a time and #1 is the only one that maked no differance. I also put a vacume gauge on the engine and it hovers around 16 in of vacume at idle. But when it is missing it fluctuates 1.2 - 2 in of vacume.

I have replaced: spark plugs, wires, crankshaft sensor, Camshaft sensor, Rotor, distributer cap, MAP sensor), IAC (idle air control), ICT sensor (engine coolant temputure), IAT (intake air sensor), the distriputer gear (it was worn), 3-O2 sensors (there are 4),

I have NOT replaced yet the EGR valve. Is there a way to test the mechanics of the EGR?
I also have NOT replaced the TPS throttle position or the MAF sensor (mass air flow), VSS sensor (vehicle speed sensor), KS (knock sensor)

I have timed it as close to 0% as possible without a scanner.
And I cannot find the wire I am suppose to disconnet on thei truck when you time it. Does my truck have one and if so. whare is it?

SO, what would cause this miss in my engine that would miss 80% of the time.

Thanks for your help in advance.

[jveik]

so you are 100 percent certain that it is missing? try taking a decent timing light and test it on another cylinder to make sure it works right and then put it on the number 1 and see if the pulses of light fluctuate. Sometimes i used to see it stop flashing for a bit and the engine would seem to be idling rougher then it would blink a few times with a smooth idle. oddly enough it was my number one cylinder lol. have you replaced the distributor itself?

maybe it isnt the spark that's the problem? is there any way that it could be not getting fuel to that one cylinder?

i would guess that your heads are not in good shape since there is 160,000 miles on the engine. maybe the compression in that cylinder is absolutely zero due to completely horrendous valvetrain.

try a compression test...

[ChevyBobby]

Originally Posted by jveik

so you are 100 percent certain that it is missing? try taking a decent timing light and test it on another cylinder to make sure it works right and then put it on the number 1 and see if the pulses of light fluctuate. Sometimes i used to see it stop flashing for a bit and the engine would seem to be idling rougher then it would blink a few times with a smooth idle. oddly enough it was my number one cylinder lol. have you replaced the distributor itself?

maybe it isnt the spark that's the problem? is there any way that it could be not getting fuel to that one cylinder?

i would guess that your heads are not in good shape since there is 160,000 miles on the engine. maybe the compression in that cylinder is absolutely zero due to completely horrendous valvetrain.

try a compression test...

I forgot to mention that I did a compreton test and all cyclinders ae a 175 PSI. I was surprise it was that good for an older engine. I also replaced the Fuel injectors. And I have sprayed the engine with water to see if it was a vacume leak or maybe a spark from the wires.
I have made sure that the timing light was good.
I did replace the distrubuter gear, it was worn. But other than that it was ok.

Like I said, when I pull #1 wire off the Distributer, #1 is the only cylinder that does not cause the engine to run worse.

Any other ideas?

[jveik]

im totally stumped. if it is electrically ok then maybe there is a lifter or cam lobe or something else in the valve train thats crapped up. i doubt it tho from the way you describe it having good compression and all... good luck though

[SpitAndDirt]

You are really throwing parts at a problem aren't you? Have you tried going to the dealer ONLY to see if you have a computer update available for your truck? Sometimes driveability issues can only be solved by a reflash of the PCM. It's worth a shot. I have 166,000 on my 96 Z71. I have replaced worn items such as the cap and rotor, fuel filter, and the two Pre-Cat O2 sensors. As for all that other junk, hell no. I have had updates reflashed into my ECM that did clear a few driveability issues. One other item: I have never done an intake gasket on my truck. It is possible that it was replaced prior to me buying the vehicle. I bought it with 40,000 miles. I have replaced the intake gaskets on two friends trucks. Both 5.7L VIN "R" engines, both 97 model years. The intake gasket tends to break at the water jacket closest to the #1 cylinder intake port. It would not surprise me that IF you were loosing coolant at a moderate rate, but it wasn't appearing on the ground or in the oil, that it was causing the #1 cylinder to misfire. Just a thought. Hope this leads you to some solutions. Oh, and as for the EGR, remove it and clean it thoroughly with a scribe or pick. Remove as much carbon as possible. Buy a new gasket and re-install. Back to the basics...... -Chris

[SpitAndDirt]

er...I bought my truck with 147,000 miles....that probably makes mores sense

[ChevyBobby]

Originally Posted by jveik

im totally stumped. if it is electrically ok then maybe there is a lifter or cam lobe or something else in the valve train thats crapped up. i doubt it tho from the way you describe it having good compression and all... good luck though

I wounder even though I did a compresion test with al the plugs out of the engine If maybe I got a bunt valve and it is only showing up at higher RPMs. I think I am going to take off the valve cover and mate sure att the valve ar opening all that way.

Any other suggestions?

I'm also going to have it put on a scanner and see if there are any plroblems.

Is it possible that the computer not to fine all the cylinders?

[ChevyBobby]

Originally Posted by SpitAndDirt

You are really throwing parts at a problem aren't you? Have you tried going to the dealer ONLY to see if you have a computer update available for your truck? Sometimes driveability issues can only be solved by a reflash of the PCM. It's worth a shot. I have 166,000 on my 96 Z71. I have replaced worn items such as the cap and rotor, fuel filter, and the two Pre-Cat O2 sensors. As for all that other junk, hell no. I have had updates reflashed into my ECM that did clear a few driveability issues. One other item: I have never done an intake gasket on my truck. It is possible that it was replaced prior to me buying the vehicle. I bought it with 40,000 miles. I have replaced the intake gaskets on two friends trucks. Both 5.7L VIN "R" engines, both 97 model years. The intake gasket tends to break at the water jacket closest to the #1 cylinder intake port. It would not surprise me that IF you were loosing coolant at a moderate rate, but it wasn't appearing on the ground or in the oil, that it was causing the #1 cylinder to misfire. Just a thought. Hope this leads you to some solutions. Oh, and as for the EGR, remove it and clean it thoroughly with a scribe or pick. Remove as much carbon as possible. Buy a new gasket and re-install. Back to the basics...... -Chris

Yes, but at 160.00 likes, moste of what I put in it was going to be needed in the future.
I am taking to to a fridn this week and have it put on a scanner. I do't do Dealers. They are too dishonest.

[ChevyBobby]

Originally Posted by jveik

so you are 100 percent certain that it is missing? try taking a decent timing light and test it on another cylinder to make sure it works right and then put it on the number 1 and see if the pulses of light fluctuate. Sometimes i used to see it stop flashing for a bit and the engine would seem to be idling rougher then it would blink a few times with a smooth idle. oddly enough it was my number one cylinder lol. have you replaced the distributor itself?

maybe it isnt the spark that's the problem? is there any way that it could be not getting fuel to that one cylinder?

i would guess that your heads are not in good shape since there is 160,000 miles on the engine. maybe the compression in that cylinder is absolutely zero due to completely horrendous valvetrain.

try a compression test...

Well I did take off the valve cover. #1 exhaust vale has a broken spring. Bt it still open and closed when I ran the engine with no taping noise.
At Idle I cannot see why that would make it miss. But I can see that at high speen that broken spring can cause the valve not to close fast enouph and possible the valve hit the piston or cause a burnt valve.
there is only one part of the spring that is broke and it is at the top.
While that valve is closed it still has tention on the rocker arm.

Any ideas guy?

[jveik]

umm... well... lol i have no clue

[GMMerlin]

Originally Posted by ChevyBobby

I do't do Dealers. They are too dishonest.

But yet you will PM me for help....after that slam, no more help from me.

[ChevyBobby]

Originally Posted by GMMerlin

But yet you will PM me for help....after that slam, no more help from me.

If you concider me spaking the truck a slam. ok.
But it is the truth.

If you are a dealer and your offended, You should not me and be proud your not like the others.

If you choose not to help. That cool also.

Have a good day sir.

[sherman69]

Originally Posted by ChevyBobby

If you concider me spaking the truck a slam. ok.
But it is the truth.

If you are a dealer and your offended, You should not me and be proud your not like the others.

If you choose not to help. That cool also.

Have a good day sir.

-------------------------------------------------------------
I have no idea what the heck you just said!
But even though some people have had problems with a dealer,
I have had a number of very good experiences with two different dealers in their service centers. I do 99 percent of my own work but occasionally a dealer is needed.
Bob B

[CustomDeluxe]

Since it hasn't been brougth up yet, did you take out the spark plug and double check that you have the correct gap? I had this same issue just last week, i replaced the plugs/wires/ect...but when putting the new plugs in, one of the plugs was dropped or something, i took them out and found there was no gap on one.

[ChevyBobby]

Originally Posted by CustomDeluxe

Since it hasn't been brougth up yet, did you take out the spark plug and double check that you have the correct gap? I had this same issue just last week, i replaced the plugs/wires/ect...but when putting the new plugs in, one of the plugs was dropped or something, i took them out and found there was no gap on one.

OK guys, here was what the problem was. A broken valve spring.
I did not show on on the compession testing I did.
I have to tale off the valve covers and phyicallly see it broken on #1 exhaust.