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-   -   Question: mis and back fire on full boost (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/402826-question-mis-back-fire-full-boost.html)

x98boardwell 04-08-2008 06:51 PM

Question: mis and back fire on full boost
 
I took my 930 for a spirited drive this evening. The oil temperature had risen to just below the 1st hash mark on the gage (194 F) and I was coming off an on-ramp and pushed the throttle all the way in 2nd gear.

When the car reached approx. 4500-5000 rpm it started to hesitate and at one point "kind -of" back fired on me.

Now, the car never did it again and I even attempted 2nd gear with hard throttle and no dice... just pulled like she was brand new.

I have a B6 Inter-cooler, K27S and GSF Headers. The car has been on the road for about a week or so since all of the upgrades and not acted up once since. The car also seems to hesitate when cold (I'm guessing fairly normal).

My thoughts,

1) Possibly running lean??? (The mechanic that checked my work and adjusted my afr's said that hew set it a little rich so the car would run better)
2) The car was too cold to introduce full boost to the equation? I thought it was just warm enough, so not sure.

Any help would be appreciated.

Thanks in advance,
Bryan

x98boardwell 04-08-2008 07:22 PM

Thoughts
 
The more I sit here and think about it, I think it's fuel related.

Possible fuel pump going bad, or something in my fuel filter or fuel injector??? I just filled up from a quarter of a tank before I went out.

Any ideas?

Thanks,
Bryan

dsiegel360 04-09-2008 05:33 PM

Are you running the stock wastegate spring? If you are running 1 bar with a stock warm up regulator, then you are not getting enough fuel on enrichment/boost. If you are running the stock spring, I assume you are getting enough fuel. What is your timing set at?

Also, if you've removed the stock BOV to install the new IC, the car will burp and fart alot. Normal.

If you lifted your foot off the pedal at 4500rpms, the car would gurgle as it goes lean. Normal.

If the car was warm and at 4500rpms-full throttle- there was hesitation, then you may have some kind of vac leak.

I'm no expert but I know that you don't want to be running this car lean. To me, an AFR gauge is a necessity. [url]www.inyourfacegauges.com is where I got mine. I have PLX but Innovate's LM-1 can be purchased used for pretty cheap.

x98boardwell 04-10-2008 07:29 PM

Dsiegel360
 
Answers,

1) I am running a .8bar (stock) waste gate spring. Not sure what the timing is set at. Remember, this has only happened once and not prior to there after.

2) With the BOV gone, I understand that the car will burp and fart on deceleration, but should not under throttle. I am curious about acceleration.

3) There is no vac-leak... we used fluorescent gas to see if there was and no dice.

4) The car was set actually a little richer than normal so the car runs better. I know at some point, the AFR gage will be the way to go.

I appreciate your input. If you have any other ideas, please post.

Thanks,
Bryan

WERK I 04-11-2008 06:11 AM

Quote:

Originally Posted by x98boardwell (Post 3875750)
I took my 930 for a spirited drive this evening. The oil temperature had risen to just below the 1st hash mark on the gage (194 F) and I was coming off an on-ramp and pushed the throttle all the way in 2nd gear.

When the car reached approx. 4500-5000 rpm it started to hesitate and at one point "kind -of" back fired on me.

Now, the car never did it again and I even attempted 2nd gear with hard throttle and no dice... just pulled like she was brand new.

I have a B6 Inter-cooler, K27S and GSF Headers. The car has been on the road for about a week or so since all of the upgrades and not acted up once since. The car also seems to hesitate when cold (I'm guessing fairly normal).

My thoughts,

1) Possibly running lean??? (The mechanic that checked my work and adjusted my afr's said that hew set it a little rich so the car would run better)
2) The car was too cold to introduce full boost to the equation? I thought it was just warm enough, so not sure.

Any help would be appreciated.

Thanks in advance,
Bryan

Bryan,
I'm leaning towards plugs. If the plugs are loaded up with soot/carbon, you'll get a mis-fire. Once you have a good hard run on them the problem doesn't manifest itself again.........Until there's another opportunity for the engine to carbon up the plugs again.bKeep in mind your mechanic turned the screw to richen the mixture.
Were you driving around town at low RPM's prior to this incident?

I agree with the others'. Put the engine on a LM-1 analyzer and track the AFR's.

x98boardwell 04-11-2008 07:24 AM

Werk-I
 
We looked at the plugs when we had the motor out. They are the expensive Bosch and looked to be just fine.

I was driving rather cautiously around town while I was warming up the motor but I kept the rpm's around 3000 while doing so and I just had exited the highway where I was going 80 at 3000 rpm's or so.

Not sure what is could have been. I took the car out last night and she drove beautifully.

Maybe it was something caught in the injector? Maybe time for a new fuel filter?

Thanks for your help.

Bryan

911boost 04-11-2008 02:00 PM

Look at the plugs again, after the mechanic richened the mixture. Mine was running wo rich that if I let it idle for long periods of time, it would build up and run like crap.

x98boardwell 04-11-2008 05:14 PM

Bsiple
 
Great point. I will do that and well see. When I had the leak-down on the car, all of the cylinders came back with 2-3% (96k miles... not bad huh) but cylinder #3 had a 15%.

Now, the engine was out of the car (meaning extremely cold) and the motor had been used less than 100 miles in 3 months time prior to the engine drop. He said the plug looked to be fine (#3) and he thought it was from the coldness of the motor and said I should have no worries after all of the others came back so good.

Any thoughts? The car runs great otherwise!!

Thanks,
Bryan

x98boardwell 04-11-2008 11:14 PM

Final Question
 
Well,

After driving the car for a week or two, I have noticed a pattern. When the car is cold... when I take off (from a stand still) she hesitates a little like she is running on 5 cylinders. As soon as I get her warm and on the throttle a bit, she runs like a top for the rest of the day no matter what I'm doing.

Is this a sign of running too rich?

Thanks,
Bryan

beepbeep 04-12-2008 06:34 AM

Quote:

Originally Posted by x98boardwell (Post 3881980)
Well,

After driving the car for a week or two, I have noticed a pattern. When the car is cold... when I take off (from a stand still) she hesitates a little like she is running on 5 cylinders. As soon as I get her warm and on the throttle a bit, she runs like a top for the rest of the day no matter what I'm doing.

Is this a sign of running too rich?

Thanks,
Bryan

Pull #1 plug (driver side, third cylinder from behind) and check it out. If it runs on 5 cylinders, this is the first one to foul the plug to bad air-flow trough plenum. What plugs are you using? You might want to try running one step hotter plugs. OEM ones are very cold.

Also, it might be a time to do a leak-down test?

x98boardwell 04-12-2008 07:29 AM

BeepBeep
 
Read further up the post. You will find all the answers to your questions.

I can pull the plug and check.

Bryan


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