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930s rule the wasteland
 
h20cooled7's Avatar
 
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Porsche Crest ever have a backfire on hard accel.

well it sounded like a backfire in 3rd gear under boost. me and a buddy were showboating saturday and he said he saw white smoke when this happend. i was accelerating hard in 3rd gear and i heard a pop,pop pop. i got out of the throttle and stopped . i thought i blew a charge pipe but everything is on. the car runs fine starts fine and i even tryed to duplicate it but it wont do it . the car was pretty warm and has never done this,but me and my buddy where driving them pretty hard . any feedback
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Old 05-09-2007, 04:23 PM
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Backfire is usually caused by excess fuel dumped into the hot exhaust system passed the turbocharger (typically on DECEL), or it could have been a lean back-fire. If the latter, be very careful and ensure your A/F's are in check. You may have an air leak around the intake somewhere (perhaps an intake manifold gasket got sucked in, creating a vacuum leak)?

Torque down your intake manifold nuts as un-metered air will cause the motor to run lean, and you certainly don't want this on a turbo motor

Has it done it again since? Whilst the motor is running, spray carb cleaner around where the intake runners meets the heads and see if it makes a difference to idle quality. if so, then you have popped an intake manifold gasket. This commonly happens on 3.2 Carrera's too... ask me how I know
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Last edited by WydRyd; 05-09-2007 at 09:49 PM..
Old 05-09-2007, 06:03 PM
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930s rule the wasteland
 
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IF I HAVE A LEAK IN MY AIR INJECTION WILL THIS CAUSE THIS ? I WANT TO REMOVE MY AIR INJECTION AND KNOW ABOUT THE PLUGS FOR THE PIPES WHAT ELSE DO I HAVE TO PLUG AND DELETE. I WANT TO DO THIS AND ILL JUST REGASKET MY INTAKE WHILE IM IN THERE. THANKS FOR THE GREAT INFO
PETE
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Old 05-10-2007, 08:13 AM
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Correct me if I am way off here, but didn't you mess around with the boost knob when you first bought the car? If that was you, than my advise now is exactly what it was then.

Tune your air/fuel ratio. Don't go chasing imaginary problems when you could have altered your air/fuel ratio already.

If it was somebody else, sorry!
Old 05-10-2007, 08:19 AM
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YA BUT IF I CUT THE VALVE ALL THE WAY OFF IT SHOULDNT HURT ANYTHING SHOULD IT? YES IT WAS ME IM GUILTY. NAMES PETE
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Old 05-10-2007, 08:53 AM
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OK IM GONNA MAKE A APOINTMENT TO GET CHECKED
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Old 05-10-2007, 08:56 AM
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That sounds like what happened to me as my Cdi was dying. I was in the middle of obliterating a Honda S2000 and heard the same violent POP,POP,POP,POP and I let off, pulled off the high way when the car died out. I was about to obliterate the fender with my foot when my friend turned the key and it fired to life. I just swapped an Msd in there and it fixed all the problems.
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Old 05-10-2007, 09:11 AM
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OK ,BUT I STILL DIDNT GET THE ANSWER FOR THE MANUAL BOOST KNOB , CAN I SHUT THIS VALVE AND HAVE THE CAR RUN LIKE IT WAS STOCK WITHOUT AFFECTING THE MIXTURE
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Old 05-10-2007, 10:37 AM
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stop typing in all caps...
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Old 05-10-2007, 01:15 PM
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why does that bother people
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Old 05-10-2007, 03:20 PM
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As you know, the more boost you have the more fuel you need.
The stock WUR settings were specked at the factory for 0.7-0.8bar and MAY go out of spec lean when the boost is turned up to 1.0bar. I say MAY because many things play into it. The only way to know for sure is to measure the A/F ratios real-time while on boost.

I have no input on your popping issue as I have never experienced it or been involvd with a car that has.

As for the caps, it is an odd mental quirk of sorts BUT ALL CAPS SEEM LIKE YOU ARE YELLING.
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Old 05-10-2007, 04:49 PM
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no stop im not yelling ,come on this is serious stuff.here ill type in lower case to drive the other 1/2 nuts. ok i talked to robert down at luftecnik down in richmond , now he said the overboost sensor could have been killing my fuel pumps. i drove my car tonight and it will go well over 1.0 bar if i push it. if i limit my boost to 1 bar will it boost the full sweep of the tach. i will plumb my system as soon as i find the factory scematic . if i remove my air injection will this interfer with my boost and how do i cap everything off? i know about the plugs in the bottom of the engine what about the the air pump and the rest of the plumbing is there a post on this procedure. and damit i dont have a mental quirk,i just suck with the shift key!
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Old 05-10-2007, 05:10 PM
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Doubt it was the OB cutoff, when that kicks in the car bucks like a bronco trying to toss you through the windscreen until you let off. This I know a lot about.. lol
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Old 05-10-2007, 05:26 PM
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as soon as it happend i let off the throttle
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Old 05-10-2007, 05:32 PM
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Quote:
Originally posted by h20cooled7
OK ,BUT I STILL DIDNT GET THE ANSWER FOR THE MANUAL BOOST KNOB , CAN I SHUT THIS VALVE AND HAVE THE CAR RUN LIKE IT WAS STOCK WITHOUT AFFECTING THE MIXTURE


As far as your question about turning back the boost, this is only a guess, but if the CIS had been tuned by the previous owner to run at like 1 bar, or even more, and you cut the boost back lower than that, you may be running rich. Hence, you simply have to pick your boost level first, and tune accordingly.....I think that if you shut your boost valve off, you should get boost according to the actual boost spring in your wastegate, which I am just guessing would have been upgraded to 1 bar, considering how much boost you have been running. But maybe it is the ole' .8 bar spring.....

But what you are saying, I think, is that you are running more than 1 bar boost. If that popping sound is from too lean a condition due to insufficient fuel under too much boost, you are seriously in danger of killing your engine the next time you drive hard and it is a hot day. As in piston melting and major rebuild and over $10,000 down the drain. There is a chance that you heard detonation, I am not sure.

Tuning your boost knob to a specific boost level, like 1 bar, and then tuning your air fuel ratio to 1 bar is the first step. I think you should consider bypassing the boost knob completely and just put a 1 bar spring in your wastegate. That is essentially what I did, I had a knob of death like you, and my boost was supposedly set at 1.1 bar but would just go all over the place, and I now run a 1 bar spring and get dead accurate boost every time in every gear, so I can tune my AFR precisely.

This is something you need to do whether or not it has anything to do with your current problem. Maybe it is related to your problem, maybe not, but it is the required first step in not melting your engine.

As somebody already said, you might have distributor problems. If one of your plugs isn't firing right, than that is bad news. I would upgrade to a newer CDI type unit for precise timing and a stronger spark, if the distributor is starting to seize up.

If you are running so much boost that you are hitting the overboost cut off, you are in serious danger of melting your pistons. But I find it hard to believe that somebody put a knob of death on your car without disengaging the overboost cut off switch, because usually that is part of the 'procedure' in hot rodding your turbo. That is something you can check, but the fact is that you have no reason to run so much boost as to hit the kill switch in the first place. You really should stay at 1 bar of boost.

All I know is that my system never stayed at one boost level until I bypassed my boost knob, and then my AFR could be set more accurately.
Old 05-10-2007, 07:02 PM
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I did not mean to say the odd mental quirk was you, the odd mental quirk is the perception that folks get when they read things written in all caps. The perception is yelling. I find that perception to be an interesting quirk, that's all.

We've been talking about your dial-a-death knob in many different posts. You really need to get rid of that thing. WURs are not designed to handle adjustable levels of boost very well. That is where the tunability of EFI really shines.

Removing the air injection is as simple as ..... removing the air injection. Take it off, cap the various hoses, plug the heads and sell the mess to some poor bastard that lives in California.

There are 2 systems that protect your engine from stretching too far. The dizzy has a cut-out at ~7100RPM and the overboost switch shuts off the fuel pump(s) at ~1.1bar.
I have never experienced the fuel pump shut off so I don't know if it would do the things you describe. I have many times experienced the dizzy cut-out and it sounds ugly. Kind of like a machine gun of sorts.
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Old 05-10-2007, 07:38 PM
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If you have seen more than 1.1 bar of boost on your boost gauge before than you can pretty much bet that the overboost switch was removed.

Perhaps you overrevved the gear to 7100 rpm? That is something you would have to rule out as a possibility....Easy to do in 2nd gear, maybe even third.....
Old 05-11-2007, 08:29 AM
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How much does the stock spring cost?
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Old 05-11-2007, 10:52 AM
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Quote:
Originally posted by h20cooled7
How much does the stock spring cost?
You may have a stock spring, or at most maybe a 1 bar spring. Take it out and have a spring resistance test done on it, or just bypass your boost death gauge and find out by driving your car.

They are cheap enough. Look it up at Pelican Parts while you are here. I think about $50, as a guess.
Old 05-11-2007, 07:26 PM
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can i run a 1.2 bar spring without imploding my motor? if i can does any1 have 1?
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Old 05-14-2007, 06:07 AM
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