Acceleration Problem

[gtcs07]

I didnt even change years it was 07-07

 

[scramblr]

Tried a different PCM and no change. Waiting for a leak down tool and adapter to do a test, although I'm confident that's going to be O.K. Bashing my head against the wall here...any and all ideas welcome.

 

[Mojave Dave]

Pretty simple, but if the ground from motor to frame is not solid, this will happen. Just a wild idea.

 

[scramblr]

Pretty simple, but if the ground from motor to frame is not solid, this will happen. Just a wild idea.

Sometimes simple is what we overlook. Can you be more specific, i.e., which ground/wire to look for? TIA...

 

[tmcolegr]

Our vehicles have 2 ground cables attached directly to the negative battery cable: 1 goes directly to the passenger's side motor mount, the other goes to the passenger's side strut tower. There is also a ground strap that runs from the back of the driver's side cylinder head to the cowl directly above the driver's side valve cover.

 

[Mojave Dave]

Yes thanks tmcolegr, you are exactly right. Easy to overlook any of the three.

 

[scramblr]

Still need to double check the neg cables, but did complete a leakdown test. Leakdown test came out <10% in all cylinders expect 3 (around 15%) and 4 (around 17%). However, I'm not 100% positive I was at TDC since I had air coming out of the passenger side valve cover breather for all 8 cylinders...or is that normal? I didn't hear air coming out of anywhere else nor bubbles in the coolant tank.

 

[lito]

However, I'm not 100% positive I was at TDC since I had air coming out of the passenger side valve cover breather for all 8 cylinders...or is that normal? I didn't hear air coming out of anywhere else nor bubbles in the coolant tank.

Yes, there is no 100% sealing inside the cylinder the rings have gaps (and specially if an engine built for boost) and that is where the pressure escapes from the cylinder, (that is why some leakage is expected) all this pressure end is the oil pan and thru the oil return passages get into the valve covers, by design the pass valve cover will realease the pressure easily.

All is ok there, shame the car is still having issues, I still think something has to go on with the bypass.

 

[scramblr]

What about the plugs being at .30. Would .28 make any difference? Would there have to be a change in the tune? Four months of this is driving me nuts.

 

[probercr93]

This scares me, and I don't mean to alarm you, but my old motor started doing this before it blew (no idea if this has any corolation with each other or not). However my new motor just had a random misfire on the same 2 cyl. as the last one. Says misfire on cyl 4 and 7. I'd really like to know what would cause this as my whole system is new except for the PCM.

 

[scramblr]

I'm not getting any codes at all and the plugs look good. Not sure if that means anything, but I don't have anything else to troubleshoot that I know of. I have a new bypass kit but not sure I can swap it out without a press for the bearings.

 

[Towelly]

We are positive your not getting belt slip or perhaps slap?

 

[94tbird]

gopro camera, mount under hood faced at belt. that will tell you for sure if you got belt slip or not

 

[Tbone]

Sounds like belt slip to me also, runs fine when no boost, belt slipping would cause the bucking and af ratio to go go crazy along with the boost gauge. Take the belt off and check the SC pulley for rubber dust in the ribs?

 

[scramblr]

Belt is practically new and not getting belt dust. I do have another new belt here so I think I'll swap and check all the pulleys. Thanks for the tips.

 

[Tbone]

Even though the belt is new, can still be slipping. I see you have a thump tensioner already so shouldnt be slipping, but really sounds like belt slip to me still.

 

[scramblr]

I have the Thump tensioner, BGG 8 rib kit, 90mm pullies on the tensioner and passenger side idler along with a 100mm pulley on the drivers side idler and a RR 2.95 pulley. Unless the tensioner is bad, I don't think that belt is going anywhere. But definitely worth a check.

 

[scramblr]

Added some videos to the first post. Tell me what you think. TIA!!!

 

[Ponykix]

Had a hesitation issue I was chasing down that was tough to find but here is what I found that may be worth a try. Plugs were new and I ran them with no problem for around 5000 miles. Car showed no codes with my
Autoguage 2. I used a dianostic scanner that would show misfires at each individual cylinder and I was getting a few misfires (very few, sometimes none) at cyl 6. I pulled the new plug an upon inspection found it was gapped correctly but the electrode was off center just a little. Installed new plug and problem solved.

I can not tell how long I chased this because I had new plugs and thought they were not part of the problem. Good luck.

 

[scramblr]

Had a hesitation issue I was chasing down that was tough to find but here is what I found that may be worth a try. Plugs were new and I ran them with no problem for around 5000 miles. Car showed no codes with my
Autoguage 2. I used a dianostic scanner that would show misfires at each individual cylinder and I was getting a few misfires (very few, sometimes none) at cyl 6. I pulled the new plug an upon inspection found it was gapped correctly but the electrode was off center just a little. Installed new plug and problem solved.

I can not tell how long I chased this because I had new plugs and thought they were not part of the problem. Good luck.

I appreciate the input...good first post. I've swapped plugs twice and have another new set on the shelf, so it may be worth a try. One thing I have not done is hook up a diagnostics scanner to the car. Eh, now that the car is in pieces (wreck), I can have the shop hook up a scanner to it and check it out. Thanks...