New Engine Low on Power
New Engine Low on Power Ok guys, looking for a little guidance. I rebuilt a 5.3 lm7 with all stock bottom end, new bearings throughout. New 4.8l pistons, ls6 cam, intake, tb and injectors. I fired the car for the first time the other day and drove it for the first time today. The problem is, it is extremely low on power and has virtually no throttle response. Engine rpm barely increases even at 3/4 throttle or more. Iam stumped here. Any ideas as to why it would seem to be so low on power? When the car is in park or neutral it will rev up fine though the RPM range and sounds to be fairly healthy.....
any insight or help is greatly appreciated.
any insight or help is greatly appreciated.
I don't kno too much about this without seeing it, but the only thing I can come up with is it might be a vacuum line. Check all of them and make sure they aren't pinched either. Good luck.
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Verdad Gallardo yea, sorry for the limited info. Its a 5.3 our of an 04 tahoe. I rebuilt it and its now in a 1980 Camaro. The ECU is from a 2002 F body. I had vats deleted from it last week and the tuner removed the rear cats from it. From what he told me it should start and run fine on this tune, at least enough to get it to him to fine tune it. The car has headers, dual exhaust and cats. Im not sure of the condition of the cats that are on it though. I was going to take it down to have an entire new exhaust put on it this weekend (no cats, just 2.5" dual with H pipe and magnaflow mufflers) I havent checked fuel pressure yet so I guess thats my next step
I'm not familiar with these engines and parts interchangeability but if the piston pin high is different you may have end up with very low compression even with the flat tops, this may be something you want to check. However if you seen the pistons @ top dead center, been at list flush with the block deck you may be OK "just a thought"
On The Tree
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from what ive heard 4.8 and 5.3 pistons are the same pin height, only difference i think is the dish in the 5.3 pistons, check your fuel pressure before anything else. I would get that exhaust done and get those cats out after that,since your going to do it anyway, or unbolt the exhaust for a bit and take it for a ride to see if it helps,that would rule out the exhaust quickly, i dont know much about stock ecu's (i run a holley hp) so cant help much there,maybe your tuner can shed some light on whats wrong, after the exhaust id say get it tuned, if the timings really out to lunch it would do what you describe, if he has no luck then check the cam and crank marks to make sure.
Last edited by 65panel5.3; Mar 7, 2013 at 11:34 AM.
well I checked a few things the other night, I couldnt find any obvious issues, cylinder 7 is definintely missing though. Also the transmission was really low. I guess I didnt put enough fluid in when I initially filled it. It took a good 2.5 quarts. I guess that would explain it not wanting to go anywhere when I tried to accelerate. But I still dont get why the engine didnt want to rev...
today, I checked and found a small vacuum leak, fixed that. Also checked fuel pressure and have a consistent 58-60psi. I also swapped out the TPS with another one I had laying around. Still no change. Very little power no matter what throttle position Iam at under load. It will rev great though in park under no load. Bad map?? I just cant seem to figure this out.....
On The Tree
Joined: Oct 2010
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you say #7 is missing? have you pulled the plugs to see what there like? how bad is it missing? could it be a bad plug or coil, id check for spark on that cylinder and see what that shows, a bad map could throw off you readings and cause some issues.swap it out quick if you have another. Are you running a maf or is it speed density? if the tune is set up for a maf and your not running one thats most likely your issue right there. Get it to the tuners and let him set it up before you go crazy looking for issues that may not be there.
A little update, I think I narrowed it down to the trans being in "limp mode". All the research I did points to this. The engine seems to being running fine but the trans is stuck in third gear (will go into 2nd if done manually) I do have reverse though. So I did a little testing and made sure there is 12v going to the trans and that the VSS is operating (I even swapped it out with a new VSS, no change) From here Im not sure what to do. How do I clear the PCM from limp mode? What else would cause this? Anything else I should check? Any additional help is greatly appreciated.
thanks for the advice, Ill try disconnecting the battery. I did that yesterday but only left it that way for about 15 min then reconnected it. I thought that would be long enough to reset everything. Ill try leaving it disconnected longer today.
Ok, so I scanned the PCM and got the following codes;
P0300--Random Misfire(which I know cyl 7 is missing)
P0351--Ignition Coil "A" Primary/Secondary Circuit (which doesn't make sense cause its cyl 7 missing, not cyl 1)
P0740--TCC Circuit
P0753--Shift Solenoid "A" Electrical
P0758--Shift Solenoid "B" Electrical
So Im thinking the reason Im getting all 3 of the transmission related codes at once is because there is an issue with the wiring or connector going to it. It just seems unlikely that all 3 of these things would go wrong with the trans at the same time. Am I wrong for thinking that?? Any Ideas?
P0300--Random Misfire(which I know cyl 7 is missing)
P0351--Ignition Coil "A" Primary/Secondary Circuit (which doesn't make sense cause its cyl 7 missing, not cyl 1)
P0740--TCC Circuit
P0753--Shift Solenoid "A" Electrical
P0758--Shift Solenoid "B" Electrical
So Im thinking the reason Im getting all 3 of the transmission related codes at once is because there is an issue with the wiring or connector going to it. It just seems unlikely that all 3 of these things would go wrong with the trans at the same time. Am I wrong for thinking that?? Any Ideas?