OK map sensor is correct, vacuum is half what it should be. I did the leak test and there was a leak, replaced intake manifold, it runs better, but map never went under 75 kpa and it should be under 60 around 55. I'm going to tear the heads back off. I am disappointed.
Any other suggestions on what can mechanically be causing map to be higher and vacuum to be lower? I'm starting to think blown rings or something.
Would a blown head gasket cause higher map and lower vacuum?
If it's something specific to just one cylinder the needle on the vacuum gauge will usually bounce like crazy. If it's steady it's something like cam timing, something that affects all cylinders equally. Unlikely that ALL the rings/pistons/valves are the cause. Same for head gasket, that should be limited to 1 or 2 cylinders and show up in the way the vacuum gauge behaves.
Holy crap batman - I thought I was the only one who ever used a vacuum gauge to diagnose things anymoreOriginally Posted by blindsquirrel
Actually the last time I used one was to diagnose a faulty ecm where out of the blue the gauge dropped and went to bouncing with throttle snaps due to ecm causing faulty ignition timing - had a bad intermittent stumble - that was a hard one, but got it fixed...
Compression test will tell a lot in this case too...
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That's exactly what I was wondering, if the ecm crapped out after 100 or so flashes. And sorry for not answering the prior question, the vacuum is correct at idle, it bounces around with rpm, when the rpm levels out vacuum stays level, when rpm jumps from 700 to 1100 the vacuum jumps with it. Idk if that info gives you more insight, but thank you all for the help.
I found a couple more things... I think lol. I'll update again after a few more tests.
OK so not all my cylinders are firing. I pulled the plugs and only half are firing. But i get no codes other than failed maf that i intended to get.
Is this a sign of a bad ecm?
This should I have been checked before anything…… can let an engine run for 20 seconds and cut it off and to a temp check on each header tube to fine this!! Change plugs and make sure Lambda is reading properly and it will do what’s it’s suppose too I bet
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On some GM vehicles, some pretty major components can have wiring issues that won't throw a code. The ecotec can have no power to the coils and it won't throw a code. Although if yours was running, how was it not triggering misfire codes if only running on 4 cylinders?
You think bad plugs are causing half my cylinders on each side not to fire? The plugs are brand new, and the half that is not firing look brand new, like they are not getting gas either. It's as if it's in reduced engine power mode but not throwing a code
REP does not disable cylinders, it only closes/disables the throttle or shuts the engine off entirely, depending on the fault.
Which cylinders are not firing?
Apologies for such a delay, sometimes work does not allow me the time to work on the car. Everything is fixed now, thank you to everyone for their input and contribution.
Rocker arms had loosened, causing multiple cylinders not fire, as if it had misfires and dead cylinders. Reset valve lash, retorqued rocker arms, actually used Loctite this time, and she runs like champ. thank you all again very much appreciated.
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How did you "reset valve lash" ?
Lifter preload is not adjustable on the LS engines (at least not when using stock rocker arms).
Lifter preload is set by varying the length of the pushrods.
i followed the ls rocker arm torque procedure, once you have set everything to zero lash, you should only be able to crank the torque wrench so far before getting to 22lbs, if too far than you need a different pushrod. Sorry if I used incorrect/confusing terminology.
Procedure: I put the 1st cylinder at TDC, zeroed out the lash then tightened the appropriate intake and exhaust valves to 22 ft lbs, which at the same time allowed me to check the load on the pushrods to ensure everything was set correctly. then i rotated 360 degrees and did the same for the remaining cylinders. for me i consider that resetting the valve lash, load, and torque on the rocker arms/lifters/pushrods. I hope that helps
Before and after retorquing rocker arms
start after retorquing rocker arms.hpl
horrible running.hpl
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