If anyone has a thought, spit it out! I want to see this lt1 powered truck STOMP some a$$ this weekend!

 

i pulled the NGK R5672A-9 plugs and installed some NGK FR4 plugs to just see if the plugs where possibly too cold.Of course there was no change at all.I think im going to back the rockers off some tomorrow and see if that has any effect on this thing at all.

This problem has stumped me, every person I know ,and appearantly the camaro board.........

 

what fuel pressure are you running? Please give specs of the fuel pump , injector and fuel pressure regulator combonation.

Once fuel has checked out you should move on to the ignition system. Either Opti or ignition module.

 

You need to track down which cylinder is misfiring, or if it is a misfire on random cylinders. I saw that you have 44lb fuel pressure, but I am wondering if it is a bad fuel injector, this is why you need to find out if only one or two cylinders are effected, then swap injectors to see if the problem follows the potentially bad part.

Second option is to take it to a reputable shop that has a scope, and pay the $90 to have them diagnose it. A scope will show the tech primary and secondary voltage and waveform on each cylinder, burn time...etc, this will accuratly pinpoint what the problem is in the hands of a qualified tech.

I see it's backfiring...out the pipe? back through the intake?

I would assume you mean out the pipe - ignition problem, get it scoped.

 

Im running a fuel cell with a1000 fuel pump with 10an feed line to pump and 8an to a y block into modified fuel rails,aeromotive fuel regulator with 8an return line.42 lb racetronic lucas injectors.

I dont think that it is 1 cylinder,1 cylinder would not have this much effect on the engine power.Im not even sure if 2 cylinders would do it.It does pop out the tail pipe with no signs of popping in the intake manifold.I have driven this truck with a dead cylinder and it was hardly noticable till i went to the track and was .3 off and 3 mph slow.When I hit the rpm range that it starts to mess up,it will absolutely not pull and more engine rpms.What ever it is is effecting all cylinders in one way or the other.

Ive already thought about the ossillascope,but I need to find a shop that has a scope and a dyno and that has proven to be difficult.

The entire ignition system is new and none of that has changed any thing.Im thinking that it almost has to be a mechanical issue with the heads,cam,lifters of some sort.

 

I rode in this thing 2 days ago and it pulls HARD until the problem happen (5800 or so) and then it will sound like a war zone in the exhaust with all of the fuel being ignited and burned in the exhaust. Kinda like a NOS system that is way rich and with the timing way slow. It is that violent in the headers. Just strange why the O2's do not show something strange here.

The scan shows 34 degrees timing constantly up there and the O2's look good also with no sign of a change. The scan shows there is no problem but a ride in the car will confirm there is a problem.

This only happens at this RPM and pulls perfect until then. It is like all 8 cylinders have the problem at the same time. You can leave it to the floor with it doing this for a few seconds and it never clears up (or blows up), it just SLOWLY gains RPM.

Lloyd

 

Do you have a copy of the program in the PCM? I didn't see anything in the scan files you uploaded.

 

I know it is along shot, but a friend of mine had a problem with the connector on the Optispark. The engine would pull hard up to 5500 or so and start to miss and loose cylinders. He swapped the opti and no change. He eventually found the wiring connector that plugged into the opti was damaged. It was not easy to see but with careful inspection you could see the damage. He replaced the connector and the problem went away. Never to be seen again. Apparently the ECM was seeing small problems with the high and low resolution signals from the opti and this was causing his issues.

Worth a check..

TOM B

 

You're running closed loop. I take it you have a BLM Locker for WOT? Is it supposed to reference cell 15 with the BLM Locker or 18, I can't remember? You're lt fuel trims (blm's) are pegged, way too rich, but your st fuel trim (integrator's) are around where they are supposed to be. It doesn't make sense why the integrator is close to 128, yet the blm's are at 108.

I would also say that 34* of timing at WOT isn't enough to see the full potetial of that cam. But worry about that after you get this figured out.

 

Here is the file that I received from Bryan at PCMforless

www.slammed98gmc.com/kmarburgercurrentapril1306.bin

 

I am by no means a lt1 programmer....
I pay someone to do that work for me.

 

No shops with a dyno and scope in dallas

Ship it to me lol.

Sounds like an ignition problem....check those connectors like was said above.

 

ok,well tonight i pulled the valve covers and loosened all the rockers.I cranked the engine and tightened them as tight as i could with my finger,then i shut the engine off and tightened down the set screws.all the rockers are tapping ,but the vibration and failing to rev up is gone.The random misfire is still there starting around 5800 and all the way up to at least 6500rpms.

I was telling Lloyd the other night when I was at his house that I cant remember if the engine was popping prior to the msd distributor or not.I put this engine together back in may.Drove it a few times and realized that It had a problem.I sold my house and moved and the truck sat over at a freinds house for a few weeks.I went and got it and replaced the opti with the msd unit thinking that was causing the vibration in the engine at highter rpms.I did not get to test it out any that day because it was 105 degrees that day and way to much traffic.It has sat at my freinds house for several months till just the last few weeks when I went and got it.

Im thinking that this msd opti could be the possible cause of this misfire that it currently has.I drove it around and adjusted on the timing screw and was unable to detect any change in the misfire.I still have my stock opti ,I may have to go install that and see what happens.

 

Yeah, there's nothing in the log or program that I saw that would cause the problem you're talking about. Only thing I can think is ignition.

 

Slammed, check your MAF Voltage Pin A on the MAF, Circuit 492 (yellow wire) should be 4 to 6 volts, your showing 2.2v - 2.14v on your log under MAT - Is that IAT or MAF voltage? (I use Auto Tap and it has different acronyms), and circuit 439 pink Pin C should be B+ (B+ Showing 13v on your log). check your ground on Pin B circuit 451 black/white wire. Pin C should come right from the ignition. This could cause the fuel trims being so high (PCM thinks there is a lot more air coming in and pulses the injectors longer)

this is madmike (that name was used by someone else on here).
Hope this helps..