keith

Hey guys - just got my Dad's 951 buttoned up (new head, new turbo) and now I am experiencing some hesitation/stumbling around 3K and 4.5K when accelerating on boost. By 4.9-5K rpm, this thing screams.

I replaced the plug wires, and the FPR, Damper, and injectors are all new.

Any ideas?


BTW, I am getting a heavy raw fuel smell in the cabin (like someone poured high-test in there) after about 20 min. of driving. It is so bad that I checked to make sure nothing was spraying under the hood (all clear). Anyone else have experience with this? It is worse with the windows down, it seems...

TIA

adrial

Do you happen to have an a/f gauge in the car?

Does it do it at WOT or just part throttle?

My car was doing the same thing at part throttle...except that I saw on the a/f gauge it was running super lean and I could smell it...I replaced the AFM, brought fuel pressure back to 3 bar (I had a 2.5 bar in there) and all seems well...

Judging by your fuel smell...mr. rocket scientist me says that you're running rich at that rpm level...

I assume the car is stock? When was the O2 sensor last replaced?

Thats all i can think of right now...

--Adrial

rage2

[quote]Originally posted by keith:
<strong>BTW, I am getting a heavy raw fuel smell in the cabin (like someone poured high-test in there) after about 20 min. of driving. It is so bad that I checked to make sure nothing was spraying under the hood (all clear). Anyone else have experience with this? It is worse with the windows down, it seems...</strong><hr></blockquote>

Fairly sure that's a loose fuel line. I had the same problem and had to wait until the leak got worse before I saw "wetness" around the area. The line affected for me was the one sitting right above the exhaust manifold... lucky I caught it before an engine fire!

Florida951

I had stumbling during boost, It was the ignition coil. I also got stumbling when my Fuel dampener went and caused the fuel pressure to rocket way up, which caused my old fuel lines to start leaking on top of the exaust causing heavy fuel smell in the car. Hope this helps. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Russ Murphy

From your description I'd go with rage
's diagnosis. If you just had the head off then you had those(ancient?) fuel lines folded back
on themselves and probably they've succumbed. Check your plugs for condition and gap if you haven't recently.

Danno

I'm not sure if you can smell a lean mixture, but a rich one is definitely aromatic. Does your power-band feel like this?



This is what Erik got while troubleshooting his high-end lean problem. Turning down the boost so that the leaning mixture in the upper RPMs don't go above 12:1 lowered the air-fuel curve from 3000rpm onwards and caused the already rich mixture at 3900rpm to get even richer. So rich in fact, it went off the scale that the dyno could record and got clipped at 10:1.

Then from 4000rpm onwards, he encountered a problem with the AFM/MAF sensor being maxed out , and/or the injectors and you get that linear air-fuel ratio line (not curve) heading up toward leaner and leaner mixtures. At some point, it crosses the ideal 12.5:1 air-fuel ratio for power and takes off. But you have to be careful because it's also heading into too-lean territory, so don't rev up your engine above 5500rpm just to be safe.

Only problem is, you can't easily dial out this mid-range richness without making the high-end lean problem even worse; you can't change shape of fuel curve with fuel-pressure/boost, only scale it up or down across the board.

keith

ok, update: chips are stock apparently. The smell has subsided dramatically, and the stumble has also, to an extent, but it is definitely still there (not like the near-bucking that it was!) Under boost, there is definitely a cloud of black smoke from the tailpipe (fuel?)

Will check pressures/FPR this evening hopefully, and get back to you guys.

BTW, when accelerating, isn't the o2 sensor no longer a factor? So, it's condition wouldn't necessarily play a role here?

Oh, and no fuel leaks that I can find.

Gnftr56

Just one possible idea on the stumble. I was chasing a stumble under boost on my 951 for quite some time, looked at plugs, vaccum leaks, wiring and even fuel pressure and couldnt figure it out. Turns out that the DME relay had frayed. Under boost and especially on hill climbs it would short out against the chasis causing fuel flow to cease and causing the car to buck like crazy. As soon as you eased off on the gas and the car settled it was ok. After replacing the relay I have had no problems.

951Tom

A new air flow meter just cured my mid-rpm stumbles.