[250Lightning]

Hey guys, I'm back in another lightning after selling my old one about a year ago. I didn't post much, so most of you probably don't remember me. Here's a pic of the new one I just got.

The truck is pretty mint, and has only minimal mods such as a K&N intake and it has been chipped. Unfortunately, the owner wasn't sure what type of chip it is, as it was done a long time ago. I'm having a slight issue with it. Anywhere up to about 3/4 throttle, things are fine. Boost builds, the truck accelerates normally. However, if I hammer down, and go WOT, the truck falls on its face.

At WOT, the RPMs build to about 4000 normally, and then they kinda stop building, truck is shuddering, the boost gauge falls to 0, and the supercharger SCREAMS. I let off pretty quick after all this starts happening. Any ideas?

 

[250Lightning]

Just wanted to add a little more info I thought of. The engine on the truck (as well as the rest of the truck) was just detailed a couple days ago. The plugs were changed several weeks ago if that helps. Could the detail of the engine be to blame?

 

[Throttle Jockey]

How was the engine detailed?

If water was sprayed onto the engine its possible that you have water intrusion past the COP boots which will cause misfires.

 

[250Lightning]

How was the engine detailed?

If water was sprayed onto the engine its possible that you have water intrusion past the COP boots which will cause misfires.

I'm not sure. The truck was detailed just prior to me buying it (today), so I wasn't the one doing the detailing, nor do I know how they did it.

 

[Throttle Jockey]

Start with the cheap and easy... pull the COPs out and see if any are wet around the base off the boot. If so you will need to use compressed air to blow the water out of the spark plug wells.


If there isn't any water then I wonder if you might have a faulty diaphragm in the boost actuator.

 

[250Lightning]

After playing with it some more today, it seems more like a trans issue. It's really apparent when you floor it from a roll. Revs fly up to around 4 grand, and the truck doesn't really accelerate or want to upshift until you let off a bit. Feels like the transmission is slipping when the Revs are higher than about 3500, whether you're taking off from a stop or downshifting.

Is there anything that would make the trans act like it's slipping? Worst case scenario, what am I looking at cost wise for a rebuild?

 

[Thegoon]

Is it doing something like what is in this thread? If so see post #2, then call the writer of post #2 and send him your tranny! :bigtu






http://www.lightningrodder.com/forum/showthread.php?t=315922

 

[TOFTS]

At WOT, the RPMs build to about 4000 normally, and then they kinda stop building, truck is shuddering, the boost gauge falls to 0, and the supercharger SCREAMS. I let off pretty quick after all this starts happening. Any ideas?

Do the RPMs go up when this happens or stay around 4K?

 

[250Lightning]

Is it doing something like what is in this thread? If so see post #2, then call the writer of post #2 and send him your tranny! :bigtu

http://www.lightningrodder.com/forum/showthread.php?t=315922

I did read that thread, and it is definitely similar. Although the RPMs don't hit the redline. It does it for the 2-3 shift as well under heavy throttle, or a big downshift from 3 to 1. Small downshifts from 3-2 or 2-1, into the 2500-3000 RPM range, are fine. Any higher, and its like it isn't catching, revs just get stuck around 4k and the truck doesn't accelerate until you let off.

As for sending my transmission somewhere, I'm up in Canada. So shipping would be absolutely killer, it'll have to be rebuilt locally if it comes to that.

Do the RPMs go up when this happens or stay around 4K?

No, they stay at around 4k, maybe up to 42 or 4300. They definitely don't hit the redline. Everything is fine up to 3500, it'll shift normally, revs and boost build normally, everything seems fine. But once you get past 3500 (which requires WOT or almost WOT, otherwise it would upshift before 4k) it feels like the transmission is slipping, boost falls, supercharger is really loud, and revs stay around 4k until you let off, then it shifts normally and everything seems fine again.

 

[TOFTS]

No, they stay at around 4k, maybe up to 42 or 4300. They definitely don't hit the redline. Everything is fine up to 3500, it'll shift normally, revs and boost build normally, everything seems fine. But once you get past 3500 (which requires WOT or almost WOT, otherwise it would upshift before 4k) it feels like the transmission is slipping, boost falls, supercharger is really loud, and revs stay around 4k until you let off, then it shifts normally and everything seems fine again.

It doesn't sound like your transmission is slipping.

Where is your boost going?

A screaming supercharger can indicate restriction but that would increase boost. Stopped up Cats or a severely dirty intercooler could cause a restriction at high RPM but I can't explain the loss of boost.

 

[250Lightning]

It doesn't sound like your transmission is slipping.

Where is your boost going?

A screaming supercharger can indicate restriction but that would increase boost. Stopped up Cats or a severely dirty intercooler could cause a restriction at high RPM but I can't explain the loss of boost.

A restriction at high RPM would make sense too. It seems like it doesn't want to rev past 4000 no matter if it is from a dig or from a downshift when rolling, and is just stuck at 4000 rpm until I let off. The downshift from 3-1 when heavy throttle is given is worrying to me, as it just feels like the trans isn't engaged, revs stay at around 4k, truck doesn't accelerate, until I let off, revs fall, and it instantly drives and shifts normally again.

I let off really quickly so its possible it might not be the trans slipping and be something else, I'm hesitant to try and drive through it and see what happens, as I obviously don't want to cause any damage.

I've tried revving it in neutral, and it goes up to 5k no problem. So it's got something to do with being under a load.

 

[Killer Ride]

It could be a Maf. Mine did something like that when my Maf was unplugged.
Also if it had a tune and they changed the maf it could also do something like that as well

 

[250Lightning]

It could be a Maf. Mine did something like that when my Maf was unplugged.
Also if it had a tune and they changed the maf it could also do something like that as well

Thanks for the advice, I'll add that to the list of things to check. I'm pretty convinced it isn't the trans, it bucks and shudders when it gets to 4k, so there must be a restriction of some sort or a misfire at high RPM. Taking it in on Tuesday to try and figure it out. Who knows what kinda chip it has on it, that could be the issue too.

 

[TOFTS]

it bucks and shudders when it gets to 4k.

Not that it changes anything, but the bucking description could be important to someone that tries to help.

I am still perplexed as to why you are loosing boost when this happens. I don't know if a roots style blower can cavitate when the restriction is too high like a barrel (Squirrel cage) fan does when it has too mush resistance or if the supply side becomes too restricted.

Other things crossing my mind are a really dirty air filter, a boost bypass that is opening up for some reason, a worn blower case with too much clearance or a similar condition with the rotors. Of course it could be just a coincidence that you have a faulty boost gauge?

I have no clue if this is what the problem is, I am just throwing out ideas.

 

[Killer Ride]

If you had the lines crossed for the Boost bypass actuator might have something to do with it. One time I was not paying attention and was able to hook up fuel injector wrong caught it in time though. Point I'm making is if whoever detailed it moved something

 

[MattACK]

After playing with it some more today, it seems more like a trans issue. It's really apparent when you floor it from a roll. Revs fly up to around 4 grand, and the truck doesn't really accelerate or want to upshift until you let off a bit. Feels like the transmission is slipping when the Revs are higher than about 3500, whether you're taking off from a stop or downshifting.

Is there anything that would make the trans act like it's slipping? Worst case scenario, what am I looking at cost wise for a rebuild?

Do I understand this correctly that from a stop the rpms jump to 4k like you have a big stall converter? Are you spinning or do you have traction during this?

 

[250Lightning]

Not that it changes anything, but the bucking description could be important to someone that tries to help.

I am still perplexed as to why you are loosing boost when this happens. I don't know if a roots style blower can cavitate when the restriction is too high like a barrel (Squirrel cage) fan does when it has too mush resistance or if the supply side becomes too restricted.

Other things crossing my mind are a really dirty air filter, a boost bypass that is opening up for some reason, a worn blower case with too much clearance or a similar condition with the rotors. Of course it could be just a coincidence that you have a faulty boost gauge?

I have no clue if this is what the problem is, I am just throwing out ideas.

Thank you! I appreciate any and all ideas, I've been compiling a list and when my old man takes it into his work on Tuesday hopefully he'll have time to check out some of these ideas!

If you had the lines crossed for the Boost bypass actuator might have something to do with it. One time I was not paying attention and was able to hook up fuel injector wrong caught it in time though. Point I'm making is if whoever detailed it moved something

Also a good idea. We will check and make sure everything is hooked up right.

Do I understand this correctly that from a stop the rpms jump to 4k like you have a big stall converter? Are you spinning or do you have traction during this?

No, I have traction throughout this whole thing. I'm reasonably certain (and my old man who is a mechanic agrees after taking it for a drive yesterday) that it has nothing to do with the trans, but instead something is causing the truck to not be able to rev past 4k rpms when under a load.

From a stop the truck accelerates normally, will spin the tires, etc. However, once it hits 4k rpm, it's like it hits a wall, and won't rev any higher. Truck bucks and shudders until you let off a bit, then it immediately shifts and drives normally. Something (perhaps a restriction as others have suggested) is stopping it from revving past 4k. This occurs from a stop, when the truck accelerates problem free through the rpm range until 4k, where the problem is, or from a big downshift, when it downshifts into that 4k range and has no power, and will not accelerate until I back off and it then shifts and runs and drives normally.

 

[MattACK]

You could be running extremely Lean or rich under wide open throttle. What is your A/F doing during all of this? Do you have an A/F gauge?

A couple of other things I would check...
1- Trace and check every vacuum line to ensure none of them are cracked and the lines are firmly seated into the boots.
2- I'd also begin pulling plugs and checking the condition and gap of them.

One more thing that may be worth looking into... I had an SCT chip on my '03 cobra a while back and began having problems with it. Intermittently under WOT it would suddenly hit a brick wall. Pulled the chip and ECM, cleaned the contacts on both, re-seated them and all was well. He might have re-flashed the chip, I don't recall but I just wanted to point out that they can also cause problems like these.

 

[250Lightning]

You could be running extremely Lean or rich under wide open throttle. What is your A/F doing during all of this? Do you have an A/F gauge?

A couple of other things I would check...
1- Trace and check every vacuum line to ensure none of them are cracked and the lines are firmly seated into the boots.
2- I'd also begin pulling plugs and checking the condition and gap of them.

One more thing that may be worth looking into... I had an SCT chip on my '03 cobra a while back and began having problems with it. Intermittently under WOT it would suddenly hit a brick wall. Pulled the chip and ECM, cleaned the contacts on both, re-seated them and all was well. He might have re-flashed the chip, I don't recall but I just wanted to point out that they can also cause problems like these.

I have no a/f gauge, the truck is completely stock other then the k&n intake and a chip. Funny you mentioned your chip, I will definitely check the chip and clean the connections.

I will make sure we check the vacuum lines and pull some plugs. They were just changed, so its possible the gap is incorrect on them when they were changed. We will be pulling codes too, that may narrow it down as well.

Thanks for all the help everyone!

 

[250Lightning]

Alright, I have an update. Truck went into the shop today. My old man found several very minor vacuum leaks, nothing major though. Plugs are in good shape, gaps are correct. I'm going to try unplugging the chip and cleaning the connections this weekend when I have some time.

He tested the fuel pressure, and its reading 30 psi when idling, and the suggested range is 28-45 psi. When the truck is off, it was 37 psi, and the range was 35-50 psi (I think?). Anyways, numbers aside, it is on the low end of the range for fuel pressure both when idling and when off.

I took it for another spin tonight. It seemed slightly better, but maybe that's in my head due to thinking the minor vacuum leaks got fixed. Really tough to say for sure. I managed to get it to go through the rev range up to 5k RPM at about 80% throttle before shifting. However, its still acting up at WOT, and hanging up around 4-4500 until I back off a little. Boost isn't dropping to 0 when it is doing this now, but the truck is shuddering/bucking a little still. It just feels like it hits a wall at WOT and doesn't want to accelerate anymore unless you ease off the throttle slightly.

Is it possible the issue is the fuel pump? That would explain why it seems to just hit a wall at WOT at the upper rev range if it is starved for fuel. I doubt the intercooler has been cleaned yet, so I'm assuming that could be an issue too.

Again, thanks everyone for all the help!