xupkid2

2 weeks ago I raced the race car at Mid Ohio and had no issues at all. This weekend at Road America I am having a boost issue. When the car is still cold the car will hold boost to redline. Once it gets warm the boost will go from 10psi to 2psi instantly once I hit 6k rpm in 3rd gear. If I shift at that point it has boost again in the new gear. In 4th gear it does the same thing but at 5700. Up to that point it will boost to 13psi and then ween off to 10psi and hold there steady till I hit the 6k threshold.

I have tried a new DME & KLR as well as verified the wastegate is working fine, even heated the wastegate up to verify under hot temp. I also checked the hoses to make sure those were ok to.

I am baffled as to what the issue could be. Not sure if its electrical or mechanical. It happens everytime at 6k rpm which lead me to think its electrical and something is telling the CV to open the wastegate.

Any ideas of things I can look at? Its not much fun short shifting.

Just for some additional info below is what the car is equipped with
- SFR Headers
- Lindsey 3pm crossover
- Stock Turbo Cup Chips
- K26/8 Turbo
- Lindsey Clubgate wastegate
- Stock cycling valve
- I do not have a MBC or any boost enhancer

Thanks
Brian

xupkid2

I guess I should also add that when the boost does cut out, it does not cut the ignition so it doesnt seem like its hitting the overboost protection. I can still get the RPM's to climb but its like an NA car.

951Saga

You could also disconnect the wastegate vacuum line to further verify it will hold boost on its own.

Tom M'Guinn

When you tried the new KLR and DME, did you use the same cup chips from your original? I've never had cup chips, so don't know, but are you sure their overboost works the same as factory street car chips? Any chance the bypass valve is failing? What happens to the AFR when the boost drops? How did you verify the wastegate was working right? Have you tried clamping the line to the wastegate and (carefully) checking to see if it holds boost that way?

951Saga

Oops, thats what I meant.

xupkid2

Tom - I did check the BOV with a known good one and it did not solve the issue. The chips I am using are the same as what was used before. I am fairly certain the overboost control on the cup chips is the same, ie: cuts ignition. As far as AFR, I dont have a gauge yet in the car so can't verify what is happening there. I plan to install one next week.

Im going to bypass the cycling valve in the morning to see if it is mechanical or electrical and then go from there. Im just stumped.

Thanks
Brian

Oddjob

Do you have stock turbo S chips that you can try?

How about a KLR Fault/Blink code test light?

Pretty sure the DME overboost protection is non-existant on any of the versions of "Cup" chips. Not sure what happens if the KLR identifies a fault and goes to limp home mode when a cup KLR chip is installed. I do not know if any functions of the limp mode is mapped on the chip or all internal to the KLR.

Trying the stock chips could eliminate the unknowns of the cup chips. See if the symptoms are the same.

xupkid2

Great idea Jim. I have a set sitting in my trailer that I can give a whirl.

Thanks
Brian

944hal

Sound similar to the problem I had with my track car. Mine is an '87, stock chips, 26/6 turbo, Lindsey wastegate, cat delete and 3" exhaust. It started out similar to yours with a reduction in boost, usually after running for awhile. Sometimes the boost would recover. Eventually, it started going into limp home mode. I replaced the DME chip with an aftermarket performance one and the problem went away. Oh yeah, the Blink code tests showed nothing on mine. I guess my point in all of this is that even though it seems as if it's not hitting the overboost on the chip, don't rule that out. Test some different chips.

Tom M'Guinn

I'd start there for sure. That's what I was getting at when I asked if you used the same chips in both sets of DME/KLR boxes. I've never had cup chips, so can't comment directly, but have "heard" they have lots of timing, no or very high rev limit, and different overboost protection.

Oddjob

Couple other thoughts:

If it was a gradual boost falloff, I would think something mechanical - but since its an instant drop from full boost to nothing at a specific rpm seems much more likely an electrical/sensor issue.

As already mentioned - certainly the cycling valve is a possible suspect.

Also, swap in a borrowed/spare AFM if you can find one at the track.

Remote chance it might be something with the knock sensor control (although unlikely)

TPS, full load signal problems

xupkid2

Finally figured it out today. The wastegate is failing once it gets hot so Ill order up a new wastegate and have it fixed for the next track day.

User 52121

Tom M'Guinn

How did you conclude that?

xupkid2

Checked all vaccum and had no issues. Replaced all electronic components with spares & bypassed the CV. When we bypassed the CV we found that it was a mechanical vs electrical issue. I came off track when everything was hot and we checked the wastegate for any vaccum and it wouldnt hold vaccum at all. We also found no consistency with the cv bypassed. When cold the was car it would go to 7psi and hold steady. Once everything was hot the pasi fluctuated drastically and then would drop to 2psi. The issue seems to be 2 fold with the wastegate. The diaphragm wont hold vaccum and the valve is sticking.