New 5.3 LM7 low on power

[70TWO NOVA]

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.

[TomM]

Sounds like its going into limp mode. Check fuel pressure at rail for starters, could be a bunch of things, need more details. Is it drive by wire, what's your trans, what is exhaust setup. Are you running a MAF or speed density tune.......... :headscratch:

T,

[70TWO NOVA]

Its not drive by wire, we are running a 4L60E. ITs MAF and headers with dual exhaust. I think the trans is low on fluid though, would this cause the engine to feel like this? I know as for transferring power it would effect it but the engine itself seems very sluggish. Also Im pretty sure I have a miss on cylinder 7 that I can seem to track down.

[barrrf]

Random misfires? Whats the code number?

Also troubleshoot your TPS.

Could also be a trans deal - if stuck in second gear. Just throwin that out there for thought because SOMETIMES my truck will not downshift to first from second after. It only does it once a great while and its never permanent.

[Rybar]

Check your O2's or possibly replace them. One of mine went bad on me.

[70TWO NOVA]

ok, i was thinking it could be the trans since the fluid was so low. I appreciate the ideas. Ill keep all this in mind while troubleshooting

[70TWO NOVA]

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 engime didnt want to rev...:willy:

[70TWO NOVA]

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.

[tooblue]

A good start would be to see what the ECM is telling you by reading the codes. With out the codes you are shooting in the dark.. Roger

[70TWO NOVA]

I bought a bluetooth adapter so I can read the codes on my phone, should be here wed. Wish I bought this earlier

[71RS/SS396]

I bought a bluetooth adapter so I can read the codes on my phone, should be here wed. Wish I bought this earlier

You can rent the code reader from O'Reillys and other parts stores, most will rent for free, just leave a deposit and you get the deposit back when you return the tool.

[70TWO NOVA]

You can rent the code reader from O'Reillys and other parts stores, most will rent for free, just leave a deposit and you get the deposit back when you return the tool.

Oh, I didnt realize they would rent those out. I bought a bluetooth obd2 adapter for use with my phone. It comes in on wed and hopefully it will work and let me view and clear codes also.

[ssable]

The most common problem that causes limp home mode is spark plug wire, next is the wiring to the coil then the coil itself. Start in that order. good luck.

[barrrf]

We should start up a pool. Or take bets.

My money is on the throttle position sensor or TPS wire going to the throttle body.

[70TWO NOVA]

The most common problem that causes limp home mode is spark plug wire, next is the wiring to the coil then the coil itself. Start in that order. good luck.
I know I have a miss on 7 cylinder. I have verified that the plug, wire, coil and coil subharness are all good. I even swapped everyting to 3 cylinder and no change. I put a noid light to the 7 injector plug and it is working properly as well. The only thing I can come up with on this is that either the wire going to the coil from the PCM is bad, or the injector itself is physically clogged. But honeslty would a miss on one of the 8 cylinders cause the transmission to go into "limp mode"??

[468Camaro]

I can tell you ive had a 5.3 for nine years and when i had a miss i could still fry the tires..03 GMC AUTO

[70TWO NOVA]

I know, there should be no reason the computer would go into limp mode over a misfire, that just seems excessive. I mean multiple cylinders or one whole bank maybe, but not a single cylinder.

[Todd in vancouver]

Funny enough I was sitting in on a class today and a similar discussion came up. According to what some of the guys were saying if you open the throttle body on a drive by wire set up manually (we were discussing cleaning and checking TB) you can throw the DBW system out of Wack and cause the car to go into limp mode. Just an FYI...

[70TWO NOVA]

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?

[tooblue]

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



I would go back and double check the wiring / routing for all of the circuits that the codes (0351-0740-0753-0758) are pointing to. Where did the harness come from for the conversion?

[barrrf]

http://dtcsearch.com/P0740/

Start there

[70TWO NOVA]

I would go back and double check the wiring / routing for all of the circuits that the codes (0351-0740-0753-0758) are pointing to. Where did the harness come from for the conversion?

thats what im going to do next, trace all the wires back to the pcm and make sure each has continuity. I bought the harness from a local company, SSP wiring I believe the name was. Seems like a really nice harness. Everything is new and well done. Im hoping a pin got pushed out of the connector or something simple.

[70TWO NOVA]

This may be a stupid question, but does the trans/pcm need an electrical input from the shifter to know what gear its been placed into? I only ask becuase Iam using the factory 1980 camaro shifter setup. There is no PNP switch or anything, just the shifter cable. I just know the 4th gen camaros had an electical switch mounted on the shifter itself and I want to make sure this isnt why Im having this problem.

[tooblue]

What year ECM are u using and what is the part# ? What year is the Trans? 4l60, 4l80, 4l70?? Roger

[70TWO NOVA]

Well I figured it out finally, the company I bought the harness from screwed up and put the wires in wrong in the main trans connector. Luckily I had a factory harness to compare to. The wires were put in 180 degrees backwards in the connector. I had to removed them all, turn the connector 180 and reinstall them. Everything seems to work fine now. I haven't gotten into 3rd or 4th gear yet but it seems to be shifting perfectly fine. Now all I have to do is figure this misfire out....

[Todd in vancouver]

Well I figured it out finally, the company I bought the harness from screwed up and put the wires in wrong in the main trans connector. Luckily I had a factory harness to compare to. The wires were put in 180 degrees backwards in the connector. I had to removed them all, turn the connector 180 and reinstall them. Everything seems to work fine now. I haven't gotten into 3rd or 4th gear yet but it seems to be shifting perfectly fine. Now all I have to do is figure this misfire out....

Great news and glad you were able to figure it out. Make sure you post some burn out pics once you get it out

[tooblue]

Well I figured it out finally, . :cheers:

[70TWO NOVA]

So far on the misfire I have; verified good fuel pressure 58-60 psi, checked the plug wires and coil. Swapped the coil/plug wire and the misfire didnt follow the coil. I used a noid light to check the inctor circuits, removed the coil sub-harness and checked all the wires for continuity/resisance, pulled the valve cover and made sure the valves were opening properly, removed the plugs (#7 is clean and shows good continuity and isnt broken internally) I fired up the engine for a few seconds and touched each header and found that cylinder 7 is the only cold one. So far everything I have looked at checks out fine. The only things I havent done is verified good coil driver circuit for cylinder 7 or checked for a physical clog in the injector. Any other ideas??

[Z06vette]

If the motor sat for any length of time, that injector could be plugged. I could not get my LS1 to start after the swap. I checked everything & nothing was out of order. I couldnt figure it out. I pulled all the injectors and soaked them in sea foam overnight. Put them in & it fired right away. Have you checked that plug- is it wet with fuel? Bad plug possibly? Scott

[70TWO NOVA]

Well I went through the harness wires (power and signals to coil connector) all the connections and wires were good. Just to be sure I pulled the wires out of a GM harness that I had and ran them instead of the wires that came with the harness. Still no change, miss on cylinder 5. I switched the coil out with one I had and it seemed to not be misfiring as bad. Maybe both my coils are bad?? I dont know what the odds of that are but Im out of ideas at this point. I think Im going to check the injectors next. I know they did sit for a while, its possible they got clogged.

[70TWO NOVA]

After scratching my head over this for a while I finally figured it out I think. Since I pretty much ruled out an ignition problem I pulled the fuel rail and injectors last night. I found a few little pieces of what seemed to be silicone sealer (the orange stuff) in the inlet side of a few injectors. I cleaned them out, but the real issue was that the #5 injector wouldnt "click" at all when I applied power to it. I checked all 8 and that was the only one that didnt work. This makes perfect sense since #5 was the cylinder throwing the code (P0305). I ordered a new injector from Rock Auto last night. Hopefully it will come by Friday so I can verify that was the issue all along.

[Todd in vancouver]

How did you make out?

[70TWO NOVA]

We figured it out. Since the ignition system seemed to check out fine, I focused my attention to the fuel system. I had good fuel pressure to the rail so I decided to pull the injectors. All 8 of them ohmed out fine, and all the driver circuits in the harness worked fine with a noid light. I pulled all the injectors individually and put power to them using a connector from and old LS harness. With 12v to each only one didnt "click". #5 which happened to be the cylinder with the consistant miss and code. I went ahead and ordered a remanufactured injector from Rock Auto (bad idea). Got it, installed it, and got a huge plume of blue smoke out the drivers side exhaust. Turns out the "new" reman injector was stick open and gas washing the cylinder. Long story short I got a GM injector from a local dealer and $140 later she runs like a champ. No miss, no smoke and ready for its final tune and dyno run on Saturday. Ill post up some dyno numbers then. Thanks again guys for all the ideas, support and for sticking with me on this.

[kainedogg]

Great job brother :trophy-1302:

[70TWO NOVA]

Thanks, I really couldnt do it without all the help. They say it takes a village to raise a child. Well I think it takes a Forum to build a Car!

[kainedogg]

Well my truck is ballsless after my swap as well and this is after a mail order tune from Frost. So since I know for a fact my motor was junkyard fodder and the injectors are equally suspect, I am going to check mine out as well. Can't get excited about twin turbos when you may have an ailing motor or system. Mine revs, but hangs for a bit :smiley_smack: