chriswtx

I want to pick some brains.. don't know if you saw my other posts, but I have been fighting what I thought was a high rpm miss for a few months. At about 5500-5700rpm the car feels like it has a miss(jerks) hard enough by 5800rpm you need to let off.. I went through everything New: plugs, wires, valve springs, crank sensor, checked crank sensor wires, pulled oil pan and checked reluctor wheel, etc... So the other night I was thinking outside the box..So I reved the motor up slowly in neutral with no load or boost(low cylinder pressures) and it still does it at 5700rpm...So pulled the belt off, reved the motor up slowly in neutral and the motor pulls clean and smooth to 7000rpm. Put the belt back on, pulled off the 2 bypass valves and just let the air free flow(no load on the blower) and reved it up slowly in neutral again with no load or boost and it still does it. Very weird..I'm thinking its an internal problem with the Paxton.. Chris from ECS is sending me a 3.25" pulley to test with and see if slowing the blower speed down moves the problem up in the rpm range indicating if it a head unit problem...

Well sorry for the long message guys..Any input would be helpful.

FactoryRaceCar

I would love to know the cause. It could very well be internal head unit problem.

Rag-Top Rick

Just throwing this out since I didn`t see it on your list....did you check all of the coils?

Anyone you could swap with short term?

Come to think of it, I had a similar problem awhile back...
In my case the coupler "in front of the maf" had de-laminated on the under side and a piece was flapping just in front of the maf wires......car ran fine in the lower rpm`s but started crapping out once the air speed was high enough to cause the piece to flap.

Sometimes it can be the least likely things that cause a problem..

Good luck!

Mike04

Here is outside the box thinking, what about compressor stall like on the compressor of a jet engine. Could the flow into the SC be getting disrupted at high RPMs and cause the SC compressor issues. Or do you have a blade bent slightly on the SC.

Try running it up to the troubled RPM with the air filter and pipe disconnected. Just don't leave any bolts in front of the SC...

Good luck

chriswtx

does it no matter what the load or AFR..not running fat..

chriswtx

Yes I havn't swaped coils yet. But if it were a coil problem I would think it would do it worse under boost. It still does it with no boost and vacuum in the manifold with the belt on. Pull the belt off and run it up in vacuum and it doesnt do it...

chriswtx

basically did that. pulled off the 2 bypass valves and just let the air free flow(no load on the blower) out of the two big 2.5" bypass holes...still did it..

exploder

Well that is freakin weird. I have followed your saga for a long time, and I wish I knew something that could help you. Here is a little good news though. Your headunit like mine will probably not be in warranty for a cheap fix from Paxton, but I did find a place here in Texas that can rebuild them from bottom to top and they are actually half the price of Paxton. www.superchargerrebuilds.com ....mine is going out to them next week to get a little oil leak fixed. Hey come to think of it since mine is going to be off anyways why don't I just send it out to you. You put it on and see if mine does the same thing on your car. Then you can just ship it out from your place to the rebuild guy and kill two birds with one stone. Maybe he might cut us a little deal on 2 at a time. PM me if your interested.

FactoryRaceCar

chriswtx

sweet offer. I was going to try and locate one locally tomorrow. There's a local shop that does alot of Paxton installs. But I might take you up on it. I will PM you...

Mike04

Did you still have the air filter hooked up?

chriswtx

yeah, i will try it without it. But its same air filter all the other ECS kits are using..

chriswtx

Hey, when I was on the phone with Paxton last night they said it was $424.95 for new bearings and seals..What did they tell you???

leojnknsC5

Backpressure? Restrictive cats?

chriswtx

no cats,1 7/8" headers, 3"pipes with open cutouts..no back pressure..

BLOWNBLUEZ06

Just thinking what about with the supercharger connected, but with the plumbing opened up where you still have the MAF connected though. Then disconnect the MAF and let it run in open loop and see. I am just thinking the more scenarios you can go through, the easier it might be isolated. It just seems to me that if the head unit had a physical problem inside that was capable of causing a hiccup like this, that it would destroy the internals. There's really not much to the guts of these things. I am kinda thinking something like Rag-top-Rick is talking about. It seems like something physical. I remember when my thrust bearing went out on my turbo, it would "sneeze" something awful because it allowed the compressor wheel to hit the housing. Maybe check the end play on the compressor wheel and look for signs of impact on the housing from the compressor wheel. Just some ideas. I hate crazy problems like this, but I also enjoy an occasional challenge.

Skunkworks

but put your hand supercharger case and see if you feel any vibration (doesn't have to be much). It's possible not sure on how likely that some sort of resonance is present that matches tunes frequency of knock sensor... did you check knock retard?

If no knock retard, then if supercharger related it may be more serious... and related to engine sensors somehow. Do you see strange belt dynamics, or event that occurs XXXX rpm such as harmonic??? Sorry just thinking out loud.

Good luck,
Mike

Rag-Top Rick

I think disconnecting the MAF is a good idea and a quick way to eliminate "it" as the problem if the issue persists with it unplugged........

briann510

Mine was doing sorta the same thing last month and turned out to be a bad impeller bearing and right at 57-5800 it was putting a huge load on the unit and stumbling and detonating. 1 impeller bearing cage was literally gone when I took it off and impeller had dropped down off center when all the bearing rolled to one side.

chriswtx

Bingo.....Thats what I'm thinking right now... Going to do a few tests tonight, then pull the head unit off...Probably just rebuild it myself...