eshane

'86 951, APE chip with banjo, 38 track days, >150,000 miles, really good car (see avatar), never had this problem before. At last event, car made full boost for first 4 laps, then lost boost for last 5 laps. Into pits, cool down for ~1 hour, next session same.......full boost first 4 laps, no boost last 5 laps. Cool down, next day - rain, much cooler outside temperature. Full boost all session (exciting in the rain!). Car has much maintenance, newer hoses, vacuum lines, j-boot, rebuilt turbo, exhaust studs&bolts, CV, Mobil 1 20-50W. Runs fine around town, full boost always. Full boost driving to track, full boost after event driving home. Heat related I'm thinking. Any ideas, experience??

bw993

Sounds like your KLR is retarding your timing and limiting your boost due to knocking. It's putting you in limp mode, which resets when you restart the car. You should check you AFR's when you are on full boost. APE chips are known to run lean at WOT.

eshane

Thanks for the idea. Does that require a trip to the dyno? Would trying higher octane racing fuel, to reduce the tendency to knock, be a help? I run Shell 93 octane pump gas. BTW, the driver was my 19 year old son. He has 9 years of kart racing experience, and may be a bit faster than me (more on the throttle and less on the brakes) Ya think?

bw993

Ways to reduce knock is with higher octane gas or lower boost. I would also suggest changing the Bosch coil to a MSD Blaster II coil (OEM swap). Blaster coil gives you more charge/energy at higher RPM (>5K) than stock ~50%.

Transaxle

Ask the KLR with the blink-code why it interacts.

GPA951s

I would put money on the Cycling valve... Its electric and its right under the manifold next to isv...

eshane

GPA951a - Could you expound on the CV causing the problem only when hot and high load? Performs just fine when not on the track.

Bit more on the car..... 2 1/2 inch test pipe, stock/old wastegate, 2-piece crossover, new downpipe, newer Beru ignition wires, newer Bosch coil, correct stock plugs and gaps, recent timing belt service w/ water pump, newer TPS, newer air circulation valve.

Car starts, idles, runs with no stumbles or hesitation, every time. No coolant overheating, even at Sebring in the summer.

At the track,when the boost does go away after 4 hot laps, the car still runs fine, no hesitation or stumbles, and finishes the sessions..........just no boost. Boxsters that got ate up down the turn 16-17 straight get to pass me back. Ugh!

GPA951s

I Feel your pain, I have had that experience before... most of the day your car is a rocket and you are blasting past other cars and then all of a sudden if feels like someone stole the turbo out of your car..LOL You think to yourself where the hell did my boost go? The next thing that happens is that you accept your fate and have to stick your arm out the window to give a miata the signal to pass..... Most frustrating.
Anyhow, What the cycling valve does is simply switch ON/OFF depending on the throttle that is applied. I will try my best to explain its function There are three vacuum hoses tied to it. One comes from where you have your "Jet" the 17mm head banjo bolt on the inlet to the intercooler..The other goes to "Atmosphere" at the inlet of the turbo (the small hard line to the j boot) and the other goes to the Wastegate. when the CV (Cycling Valve) is "Off" this circuit is basically disconnected... allowing for no boost to be made (Potential boost from intercooler pipe -----> to Atmosphere J boot) . anything that the turbo makes for Zero throttle to basically 1/2 throttle goes nowhere..... When you Hammer the Gas pedal (past 1/2 throttle) a 12V signal is sent to the CV allowing the circuit from that inter-cooler pipe Directly to the wastegate. This is why closing down the orifice on that banjo bolt will give you more boost. ALSO This is exactly why people install a "Boost Enhancer" into that circuit. The Boost Enhancer basically Closes off that Circuit at the lower end of boost However it opens up when a set level of boost is made. When it opens up the CV gets switched on and that "Jet" takes over giving you your upper level of boost. It makes the car have allot more torque down low and it feels like a go-cart...
The CV is a simple "GATE" of diverter valve. It is a selinoid has a diaphragm, coil, ect in it.. They will fail over time, what you are experiencing is that exact failure mode, however it is intermittent. no boost is the only result of the valve not firing off when it fails . It will still idle. start, run perfectly. This is an electrical component with a coil in it... When the coil fires off it is essentially an electromagnet the pulls a steel plate inside moving the diaphragm to allow the completion of the Banjo bolt to wastegate Circuit. While you do this job replace your wastegate hose and your problem should be solved. Due to the valve firing off constantly at a track day and the heat of the engine is why they fail typically at track days and not necessarily on the street. I believe the coil is weak in yours and once it gets "heat soaked" it fails. I have a dual port wastegate now on my track car and have eliminated my CV, but I still carry one with me to track days for other 951 guys..
I will post a pic of the valve and location on my next post. I happen to have a complete factory engine out of my 88.... Hope this helps... let me know your progress.. - G

GPA951s

Humboldtgrin

fast951

All good suggestions. My guess is a CV going bad or knock.
Read the KLR codes.

To detect knock, Visual knock is a good tool to have, as you know the moment the KLR detects it. For more details go to V-Knock

jerome951

Have you noticed low system voltage? I had a case where the alternator,voltage regulator & grounds would get hot after a few laps, reducing voltage to the DME & KLR, and they would limit boost. That was accompanied with the ! warning light, though, so I'm sure you'd notice that.

Chris White

What do you mean by 'no boost'? Could be in 'limp home' mode which is reduced boost brought on by the DME/KLR sensing a fault. If you mean absolutely no boost then thats a whole different thing!

eshane

Chris, I wasn't driving, but my son said "no boost". He may have been too busy, it was Sebring, to notice if the "low voltage" light came on. He said the car drove just fine for the remaining laps, but he just could'nt blow the doors off the boxsters and old 911's down to turn 17. BTW, I just filled the tank with Sunoco GT2 racing fuel, at $9/gal., but the next event isn't until February and it has full boost on the street when not heat soaked. So............we'll see.

eshane

What do you think?
https://rennlist.com/forums/924-931-...l#post14775820