hessitation/stumble after 10 psi?

[myskyon]

as the title states my 87 951 hesitates at any psi above 10. as far as mods go: LR 3" turbo back, MAF / mafterburnner, 3bar FRP, boost gage, boost controller, spec stage 2 clutch, LR hard pipes, msd blaster coil. and i just recently replaced the brake booster and line to it also with the lines for the idle stabilizer. i have gone over all of my vacuum line and cannot find a leak anywhere. i have also just replaced the plugs to Bosch platinums. i don't know what could cause this. i hear what sounds like air on the passenger side of the intake manifold but i cant find a leak anywhere? could it be the manifold was not tighened down all the way? the engine was replaced not too long ago and this is the second to last problem i have to fix since i got it back from the butcher shop.i am about to take it to the dealer to see if they can find the problem. but i don't want to spend that kind of money.please help. if you need more info i can get it for ya too. oh BTW my A/F gage sometimes reads only lean but mostly reads good. depending on the weather.

[IanS]

Why did you switch to platinum plugs? Everyone I know recommends either copper or iridium for turbos.

I would pressure test the intake with an air compressor. Then you'll know if there is a leak and where it is.

Try those two things first because they're cheap and fairly easy.

[myskyon]

OK now how would i go about pressure testing the intake? is it something i would have to manufacture myself to get it done? copper or iridium? hmm OK

[nynor]

copper.

[IanS]

If you have an air compressor, you can get a regular air hose quick-release with threads on the other end and a PVC endcap(either 1.5" or 2" I believe) from home depot/etc. Then drill a hole in the endcap and thread the air compressor quick release into the hole. The plastic is really soft, so you won't need a tap.

Then disconnect the pipe going into the intercooler and plug the cap in its place and pump up to about 10psi and see what leaks. Usually the leaks pop up immediately at a few psi and nothing new comes up at higher pressures. There are other spots you can connect the air compressor to, but I find the intercooler inlet the easiest to access.\

And I agree, I use copper.

[xero]

those bosche platinums suck I had a set of those +4's EXPLODE while installed in a 928, the ceramic part of them just shattered, the center electrode on those is just so small, I use the Bosche "super" plugs, they come in a green and yellow box and they're $1.19 at kragens

[nize]

the spark plug issue has been debated over and over again. the general consensus for the best 951 plug is NGK BPR6ES.

[nynor]

and why is this? (not picking on you, genuinely curious.)

[nize]

on rennlist over the years, various people dyno-tested dozens of plugs to get a definite answer, and NGK's consistently made more HP. every time a 'new and improved' plug is introduced (like the bosche platinums, which are a scam), someone always back-to-back tests them against the ngk's and none have beat it yet.

there is actually one plug that is the king of them all, which are the ngk pure platinum racing plugs, which have a solid platinum core electrode (not like the needle-thin wannabe electrode bosche tries to pawn off), but at more than $50 per plug, they're not really worth it for the small performance gains;
http://www.ngksparkplugs.com/products/racing/racing.asp?nav=16100&country=US

[myskyon]

yeah well i went and but the supers back in and it made a huge differance. so i am happy now to get some ngk's thankyou guys for all the help.

[myskyon]

also now that i have replaced all of my vacume lines my hesitation only comes when at 4500+ at more that 10psi. no i have another question on this same subject. my klr vacume hose has been disconnected sice i installed my boost controller should i have it hooked up? would it think there is an overboost situation at 15psi? or do my LR chips take that away?

[nize]

1) what boost controller did you install ?

2) what a/f gauge do you have ?

if your a/f gauge is sometimes reading only lean and you've removed the line to the klr to install a boost controller, you're well on your way to creating a money pit lemon 951.

[legion]

Bosch specifically says that the Platinum 2 and Platinum +4 plugs are not for use in turbocharged vehicles (though they neglect to put that on the packaging). A friend of mine who works for Bosch says that the cores of their platinum plugs is actually an nferior material to copper core plugs.

[myskyon]

Originally posted by nize
1) what boost controller did you install ?

2) what a/f gauge do you have ?

if your a/f gauge is sometimes reading only lean and you've removed the line to the klr to install a boost controller, you're well on your way to creating a money pit lemon 951.

i have insatlled the "greddy profec b" electronic boost controller and i have a "huntly racing" A/F guage. i have never had a problem befor i took it to this shop allways good readings. im now allmost to good reading with the stuff i be fixing. biggest one was the vacume lines and exhaust. also i have not removed the klr i have just unhooked the vacume line that runs to it. and removed the cyclic valve. the klr is still in the car. i am just using the mafterburrner (a piggy back fuel controller) to adjust the A/F.

[nize]

wait a minute, were you out at the nogruppe triple-xxx rootbeer porsche show sunday?

[myskyon]

yes i was

[nize]

okay i'm the guy with the red89, the only 951 there with a steam vent mod and mylar hood insulation.

pm me your number/email and let's get together, i'll help you troubleshoot your car, etc.

nize2 at msn.com

[nize]

by the way, i'm pretty sure that the huntley racing a/f gauge is narrowband, so it won't really tell you much.

are you using the stock wastegate ?

you should replace that vac.line to the klr. that's pretty important.

the cyclic valve is also pretty important, but i'm guessing the greddy ebc has knock control built in ? if not, i'd take that out too.

[myskyon]

ok so i will replace the line to the klr and see about that. yes i am using the stock wastegate not shimed. no the greddy doesnt have a knock sensor in it. but i do also have a MBC that i got from lindsey racing.

[nize]

if i were you, i'd set everything back to stock configuration and start over.

since your old motor grenaded, and since this is a different/used motor, you have no idea what the condition of this motor is, and all of the old tuned settings would be different.

boost increases should be among the very last stages of tuning, and only done after you're 110% sure everything else is running correctly first.