help, engine acting weird
11-04-2010, 12:55 PM
#1
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help, engine acting weird i went to pick my car up from getting the ignition fixed on it and i go and leave drives out fine do a u turn and it falls on its face missing and barly able to move then after like 3k rpms it instantly lights up full power and goes then stumbles and stuff i go back to mech shop and ask them to take a look, when i start it back up ran fine, went to drive around again, ran great for the rest of the night, then this morning ran great going to work, make a 7/11 trip ran great as soon as i pull in the parking lot it does it again and stumbles and cuts off, start it back up limp it into a spot and shut it off and walk in to get stuff come out, ran great back to work, at lunch i went back to mech shop to get codes checked, only ones that came up were o2 sensor and egr codes which i knew about ( was thinkin maybe MAF sensor) go to leave it falls on its face and runs like crap the first mile back to my house, then the last 1/2 mile it drove fine and parked it.
also last night it was running fine but was making almost a knocking noise kinda like spark knock, shut it off started up and has never done it again, oil pressure was fine and it felt fine just heard a noise. what do you guys think it is? fuel pump, MAf and fuel pressure regulator were my thoughts but idk.
thanks
also last night it was running fine but was making almost a knocking noise kinda like spark knock, shut it off started up and has never done it again, oil pressure was fine and it felt fine just heard a noise. what do you guys think it is? fuel pump, MAf and fuel pressure regulator were my thoughts but idk.
thanks
11-04-2010, 01:41 PM
#3
Disconnect the MAF plug and see if it clears up, The car will go into Speed Density Mode and if it runs fine then its a bad MAF. If you have access to scanning software or a GM tech II then you should get some data on it. Generally most can see issues once the data is looked over.
BTW before I forget, what did the shop did to "fix" the issue.
Also you may consider a burn or cracked ignition wire. You need to pull them all and inspect.
Run a Fuel Pressure guage and put a 100% WOT Load on the motor ( you may need to find a desolate piece of road) and see if the FP drops more then 4-5 PSI.
Everything points to part throttle and IMO tune or MAF related.
BTW before I forget, what did the shop did to "fix" the issue.
Also you may consider a burn or cracked ignition wire. You need to pull them all and inspect.
Run a Fuel Pressure guage and put a 100% WOT Load on the motor ( you may need to find a desolate piece of road) and see if the FP drops more then 4-5 PSI.
Everything points to part throttle and IMO tune or MAF related.
11-04-2010, 04:18 PM
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like the steering column came loose so they got a new one and new bushings for the tilt wheel and it was messing up the ignition cylinder, and the shop is my dads friend and ive know him personally for the last 5 years and have been gettin stuff done by him so im pretty sure they didnt mess anything up, and now that it does it more this is how it acts, ill start it up drive it for like 2-4 mins and its fine, then it will start accting up and missing or what ever, rev it up once or twice drive for a sec and it will be fine for the rest of the drive home, ive been meaning to do plugs and wires on it but the weather has gotten shitty, i ment to hook a fuel pressure gage to it today before i got off but didnt get around to it
11-04-2010, 04:33 PM
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o and what happens if i just unplug my MAF and drive around? cause its never messes up long enough to like pull over and unplug but i can try, if not i might just drive around with maf disconnected and if it doesnt happen then its maf?
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11-04-2010, 07:13 PM
#8
These are the numbers you're looking for with that fuel pressure gauge:
55 to 60 psi with key ON
-3 to -10 psi of the above numbers with engine running
When you shut the engine off the pressure should bleed very, very slowly, over a long period of time, not immediately...
55 to 60 psi with key ON
-3 to -10 psi of the above numbers with engine running
When you shut the engine off the pressure should bleed very, very slowly, over a long period of time, not immediately...
Last edited by myk; 11-04-2010 at 07:19 PM.
11-05-2010, 06:36 AM
#11
I myself never relied on the engine running method. I took the car out and gave it a good run as when the FP needs to be at its best. There should be little or no drop off. When my LT1 FP went it was dropping 10-12 PSI off of the peak under load.
