CPR

Spark Plug gap +/- .01~.03 (in either direction) will not cause that.

How much boost are you running? With that size turbo mated with the APE chips, anywhere north of 16psi will immediately send you to KP clip......possibly even 15psi.

If you are below that, then I would immediately check every hose coupler & IC pipe connection first, then each vacuum line, then Sensor connect, etc......

As an aside, did you properly grind the manifold & reclock the 27/8 so the IM can sit flush? Would not be the first one I have seen that wasn't, as it appears to be properly seated.....

lee101315

A lot of great advice here, here are a few details I may have left out. A few months ago, I changed everything that was rubber in the engine compartment. The intake manifold was removed, I changed every vacuum line, deleted the cycling valve, upgraded the isv hoses for the newer style, and changed all the intercooler and turbo hoses. Also, I did change the factory bypass valve for a new one.

The chips I have now are Lindsey racing afm chips, specifically mapped for the k27/8 turbo. The car runs much better than it did with the autothority chips, but unfortunately the same problem is plaguing me.

Being that I am running chips and no cycling valve, I do not have overboost protection. As a matter of fact, I accidentally swapped the two lines to the tial dual port wastegate and saw nearly 30 psi momentarily, and the ecu had nothing to say about it....

CPR, I did reclock the hotside of the turbo, loosen the headers, and align the entire exhaust system before tightening everything up. I did not want any exhaust leaks or cracked headers in the future. The compressor of the turbo was clearanced before I bought it, as it came off of another 951. When everything was installed, I double-checked all vacuums and smoke tested everything before starting it.

But I haven't checked the fuel pressure yet, and I haven't tested it with 1bar pressure at the fpr as elargentino suggested...

I checked the reference sensor gap readjusted it to .8mm
And also after going for a long drive, the car is very responsive and runs well, but any time it's under full load for 3-4 secs I get that nasty misfire... I'll take a crack at it tomorrow with some fresh ideas you guys gave me. I really appreciate the help so far!

lee101315

Oh and I'm running 15-16psi

CPR

Then I would say the OEM intake is no longer adequate. Time to change to a MAF with proper plumbing. Not enough air, and add with heavy fuel (warranted)= choke+cough+blacksmoke+sputter.

Rock

This is wrong info. I dont know if Lindsey Chips remove the "overboost" Knock protection. It IS not a boost protection, and has nothing to do with boost. If the engine senses knock, it goes into limp mode which is exactly what you're describing. Have you tried unplugging the knock sensor?

Ive spiked 25PSI on Stock chips and havent had it kick in.

Where are you getting the info that your knock protection has been removed?

Rock

After further reading your post there is now no doubt in my mind that you are hitting knock protection.

Also make sure that the line from the intake manifold to the KLR is not broken or disconnected. If the KLR sees atmospheric pressure and you're under 15-16 PSI then uh oh.

The cycling valve has ABSOLUTELY NOTHING to do with knock protection. Removing it does not remove the DME's ability to retard timing.

Turn the boost down to 13 PSI. Run it at open throttle, see what happens. Make sure youre running Premium too....

86 951 Driver

This sounds like my problem. Change the FPR to one that is the right size. I imagine you need a 3 bar FPR.

Oddjob

There is some confusion here between the DME overboost protection (fuel cutoff) and the KLR knock protection (KLR retarding the DME igntion signal by a few degrees ). There is plenty of historical information on this forum that correctly explains these two functions.

The KLR knock protection should not cause a stumbling miss-fire.

lee101315

Problem solved!

The problem was the manual boost controller. I had only been testing the car in town, and any 3rd gear runs were done quickly here on rt 1+9, so I could only peek at the boost gauge quickly. So I took it on the highway for a nice long drive on Sunday and it finally occurred to me!

While testing, the car would never appear to boost more than 15-16 psi, where it would run fine. Intermittently, I would get a boost spike to 25psi!!! Knock would occur (as Rock mentioned in his last post) and the DME would pull timing to compensate...causing all the backfiring out of the exhaust.

So I left the upper hose of the wastegate off, and with 10-11psi there isnt anymore issue (and far more power than the k26 at 18psi)

Elargentino was nice enough to give me his number to discuss a few things, and he told me a ball and spring type MBC is not meant for a tial dualport wastegate, and to order a Lindsey racing air regulator type of MBC, which I will do this evening.

Thank you to all who took their time to help, I appreciate your input greatly.

I should also be very thankful I didnt destroy any headgaskets or melt a piston in the process.....

minho78

Lee I hope that 1&9 has new pavement, the last time I drove there it was a mess by the Pulasky skyway.

lee101315

Yea its still a mess, theyll be doing construction there for the next two or three years...Did you drive on the Pulaski towards Elizabeth? Its my personal favorite stretch of 1+9, no places for cops to hide

minho78

Yes it used to be a nice place to take it up to some good speed. Actually we always played arround coming from clubing in the city.I'm getting old.

GPF

Glad you solved your problem - but if you had said that you did not have an MBC it would have been solved in the 1st post! (that "ball and spring type" is NOT an MBC - it sounds like a boost enhancer?)

However, as Jim (oddjob) said, there has been some confusion over other things here which I think needs clearing up or it will confuse listers reading this in the future....

The DME does not pull timing - that's what the KLR does. And if you go in to limp mode it will not reset instantly as waslike you described in an earlier post. You were hitting the DME's overboost protection which cuts fuel because boost was too high for your chipset - not because of knock.

Hope the MBC fixes it for you.