in cylinder compression

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in cylinder compression

Postby JEFFMTEKK1 » Tue May 03, 2016 10:44 pm

Hello all. I have a 04 pontiac gto ls1 vin g engine. The questions I have is does anyone have cylinder compression waveforms of ls1 vin g engines. It appears that running compression is a bit too high and the exhaust opening happens too soon. Dont know for sure though. The capture I have is of cylinder 1. It starts out crank under wot, then i released the accelerator and let engine Idle. I also have cylinder 1 secondary there too. The problem I have with this car is that there are missfires at idle while it does misfire above idle it not that bad. Under wot conditions the o2 sensors stay lean but fuel pressure is 60 psi and the engine bogs severely. The map sensor is reading between 15 and 16 inches of mercury at idle baro is 29 inches. looked at sencondary and firing kvs are very high ( btween 15 to 30 kvs at idle). There are several mods on this engine but internal mods are unknown. I think there may be a wilder cam or a adjustable cam sproket but am not sure. Any help is greatly appreciated. Thanks, Jeff
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Re: in cylinder compression

Postby STC » Wed May 04, 2016 7:45 pm

Hi Jeff.

It would help if you were to upload the PSD Files of your captures.
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Re: in cylinder compression

Postby JEFFMTEKK1 » Wed May 04, 2016 11:56 pm

Pontiac_GTO_2004_20160503-0002.psdata
(4.82 MiB) Downloaded 67 times
oops I thought I did upload the psdata. It should be here in this post now.
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Re: in cylinder compression

Postby STC » Thu May 05, 2016 9:12 pm

Jeff
First, I do not have a good waveform that you ask for.

Looking at that capture the Cylinder Pressure is consistent, but Cylinder 1 Kv is all over the place. My thinking is that if the valve timing is out that then would be a Permanent Mechanical Fault / Modification. Surely the Kv Readings would be consistently Bad ?? Even if it had Variable Valve Timing (if fitted) Issues that would be reflected in the Compression capture, so too would hydraulic tappet / Oil pressure issues. I'm on a learning spree here so feel free to shoot me down / teach me.

Under wot conditions the o2 sensors stay lean but fuel pressure is 60 psi and the engine bogs severely.


Is Fuel FLOW within Spec ??

I would like to see a Captures of
CKP / CMP / O2 & Injector 1 at Idle with Misfire Present
CKP / Inj 1 / Cyl 1 Kv / O2


Would be good to know if the misfire is consistent in particular cylinder(s) or completely random.
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