I agree with Josh. A mostly stock car with an exhaust and 15 psi with a very good chip tune is 240 whp.

 

240.... results? Its late..

 

oh man, another 951 in san diego that I haven't part, 228rwhp is my guess

 

230-260

 

for the local guys, I took it over to JBA Performance in Kearny Mesa.

It didn't go well yesterday. We couldn't get a clean run.

It would get up to around 4200 rpm in 4th gear and the car would start to buck. at that point boost was at around 11 lbs and a/f at 11.1.

We hooked up a fuel pressure gauge. It was at or around 40 then would drop right to 20 and go from 40 to 20 while bucking. It would also go lean at that point.

We tried about five different times and same result at the same rpm.

It seems like a fuel delivery issue but the thing that makes this so strange is that I can't duplicate on the street. right after the dyno, I did several 4th gear runs on the street, WOT and the car pulled hard and smooth to redline.

At this point I'm not sure what to think...

 

I've seen issues with the dyno's electrical equipment interfering with the car. What was hooked up to your car besides the fuel pressure gauge? RPM meter and where was it tied in?

 

Josh B

I'll have to check with the shop as to what else was hooked up and where...I'll get back with that info.

 

Poway, sir. Further east of Del Mar

Regarding the fueling issue, loading of the dyno shouldn't have any effect on fueling so I'd have to agree with Mr. Josh B about electrical interference, maybe the pump/DME is close to some big electrical stuff that's throwing it off...

 

I spoke with the shop - we had nothing hooked up to the car other than the a/f sniffer in the tailpipe and a boost guage tee'd in to measure boost. They do a test at 60 mph and look at rpms there to calibrateso no rpm meter.

We even took the boost guage off after a couple of tries, at that point the only thing taking a reading was the a/f sniffer and the dyno itself reading hp and torque.

He did say that the dyno is an electro magnetic dyno, but they've done dyno days in the past where they did 15 Porsches in a row, some of them 944 turbos and have never seen this issue.

as a note, I did have the DME and KLR sitting on the pasenger floorboard rather than in the footwell, as I've been changing chips in and out recently and haven't gotten around to putting them back on the bracket and back up in the footwell.

It's a mystery and as long as the car is performing well in real life I'm not sure that I should worry about it too much. I don't want to start throwing parts at it just to make run well on the dyno.

 

I had a very similiar issue recently and it turned out to be a bad injector. Was right at 4500 to 5000 rpm as well. The car would go lean and feel like it was running on 3 cylinder which it probably was. Would only show up now and then but seemed to get worse. It was consitently doing it on the dyno with their RPM meter hooked up.

Course with the fuel pressure dropping too it could be a loose power wire or ground to the fuel pump that for some reason was acting up at the dyno... I wasn't seeing a drop in fuel pressure with my issue.

Might not be a bad idea to check those connections and also have your injectors cleaned and flow tested. Or just pick up a spare set of injectors - I think stock ones go for cheap.

 

Check the boxes and chip. Maybe a bad connection

 

fourth...to redline? city streets?? you were movin dude.

 

lol! it was maybe just under 6k rpms but yeah I was movin

 

How old is dme relay? A fuel Pressure drop can be from the pump breaking up, the regulator opening or a injector hanging open. If the car stayed lean then the injector most likely isn't the culprit as it would be rich. Hooking a labscope to the pump and watching the waveform as well as checking pump rpm will provide some insight

 

The dme relay is at least 6 years old, which is when I purchased the car.
I'll take a look at the pump. I don't think the regulator is it but how can I test?