Well, I got the car back today, and it's still got the same problem. Tried swapping out the KLR with a spare that Tom loaned me, and it still does the same thing. Guess I really need to check the codes at this point and see if they are any help.

 

This is really irritating. I checked for codes after causing the overboost problem, and it didn't show any codes at all. Anybody got any other ideas?

 

The afm is bad. The spring may have lost it's tension It's probably sending a higher voltage to the dme than what it's ingesting. Have your buddy swap it out with his.

 

If it doesnt show up as KLR fault, then it is likely the DME fuel cutoff issue. You may want to swap the DME unit as a test also (if you have not already). I thought I recall that you mentioned earlier that you had swapped the AFM. If not, then I also agree that you should also check/test/swap the AFM.

Does it happen absolutely everytime 3-3500 in 4th, or is it an intermittent problem?

Sorry if any of these questions or suggestions are redundant.

 

Quick update for our esteemed panel of boost meisters. Had a little time with car last night as we installed SS brake lines (nice DOT parts from Paragon, a great way to spend $60 IMO) and I reconnected the open-to-the-air line from the side port of the wastegate to the capped line off the IC banjo T connection. Thus, I've got a sealed system at IC pressure going to the top and side port of the WG.

Boost meter now responds predictably and less irratically than before, but still seems capable of climbing to 2 bar, which slightly nixes the theory that this rig would make the WG operate like a single port unit with 1.2 bar (or so) soft/safe mode. But, no problem, really as I'm now watching the boost gauge more than the tach until things are sorted.

Lindsey Manual Boost Control on order, should arrive today. I'll put it in line where I patched the hoses together last and share a full report. I hope to get the thing settled in around factory limits first and foremost, then consider a long term strategy for boost management.

 

The waste gate spring mite be a 1 bar or over. A 1 bar spring will give you 2 bar on the factory gauge.

 

I can duplicate the problem every time without fail. 4th gear, starting full throttle from around 3000 it will cut out at 3500. I did replace the AFM a couple of months ago, but it was with a used unit, so there's not really a guarantee that it isn't the problem. I'll see if Tom will loan me a different AFM and DME so I can try swapping those two items out (one at a time) to see if either fixes the problem. If it is the AFM, I may just go ahead and get a MAF instead of spending more money on another AFM that I'll replace eventually anyway.

 

https://rennlist.com/forums/showthre...otection+Stock

Evan, Lefty,

You might want to take a look back through this old thread I started. There was some good info from a couple guys on how the chips, DME and KLR work. I learned quite a bit through the discussion at the time. Unfortunately, after I thought I had figured out the problem (bad AFM?), the car has still tripped the overboost protection on occasion.

At least there may be some comfort in knowing that a lot of guys have struggled with this type of problem....

 

Thanks for the link. I would say that misery loves company, but this is far from misery because the reward for figuring things out is immense with these cars. This is a helpful community of experienced hands worthy of the engineering we all tinker with.

 

Lefty, are you only using the factory boost gauge? If so, this is just not smart.
It is inaccurate at best.
Installing a real boost gauge is just too simple not to do. I started with one from Pep Boys (forget the brand) - it was like $20.00. It actually was very accurate, and was a vacum/boost gauge. I'd recommend this, as the vacum side will go a long way toward diagnosing possible vacum leaks (which I had, and didn't know it). Remember - a vacum leak becomes a boost leak. When the vacum is around 18 - 20 inches at idle, the system is relatively leak free.
I feel these are the first steps in solving boost issues - a leak free system and knowing exactly how much boost is blowing around in there. Playing with WGs and boost pressure beforehand is playing roulette... Next is knowing your AFR...
My 2 cents.

 

Sage words and useful numbers.

 

Well, after all this headache I finally figured out it was the AFM causing my problems. Took apart my original one, cleaned the contact strip and reinstalled it, and the car now runs fine. Just goes to show that used parts are sometimes a real pain in the butt. I guess I'll take apart the used one, and clean it and see if it works fine after cleaning. If so, I guess I can always sell it on Ebay.

 

Glad to see you figured it out. How does your 97 lt4 compare with the 951 s on the happy meter?

 

They are both a blast to drive, but for different reasons. The LT4 Firehawk is more of a brute force approach. Tons of torque off the line that will instantly send any size tires up in smoke (including the 315/35R17 R compound tires I use for the track). Wide track, long wheelbase, stiff suspension and wide tires. Great handling (actually runs laptimes within a few seconds of the Z06 I had at our local track, and I have no doubt it would toast a stock/nearly stock 951/951S), but it still has a decent ride and get decent gas mileage (of course, with a .5 overdrive you'd expect it to). Plus, being only 1 of 29 made it's got that rare factor when I take it to a cruise or show. It's only real problem is that it weighs somewhere aroudn 3400-3500lbs. Overall, I'd describe it as the ultimate "muscle car".

The Turbo S on the other hand, is much more nimble but still has a decent ride, but then it also weighs probably 500lbs less. The weight difference is very apparent, and you can feel it in both the handling and the ride. Not too say that the Firehawk doesn't handle great, in fact I'd probably take it over the Porsche for a track car, but you definitely feel the weight difference and have to adjust your driving style a little for it. One big plus for the Porsche is the seats. While the Firehawks interior design is ok, the seats suck. Porsch on the other hand, knows how to make a seat that is very comfortable yet holds you really well too. The biggest thing with the Porsche though, is the turbo. When the boost hits, it's incredible. With the DP wastegate, EBC and test pipe on my car, it hits WAY harder than any stock/chipped 951 I've ever been in. The other thing that's really fun about the Porsche is the sense of effortless speed that you have. I've never driven another car model that accelerates so quickly and effortlessly on the highway. Also, if you like looks, the Porsche will beat out the Firehawk everytime. Even with degraded condition of my car (needs new header panel and headlight covers aligned at least), I still get comments on it quite often from complete strangers (even more than my red Z06 did).

Anyway, I love them both. The Firehawk I doubt I will ever sell just due to its rarity. The Porsche, now that I've got the problems all ironed out, makes a really fun daily driver. Since it's already got some body issues, I don't mind driving it everyday, and don't have to worry about new door dings etc. I do plan on getting it fixed up a little more, but honestly I'll probably never try to get it to a 10 as far as the body goes. I enjoy driving it too much.