Well I have been having a gremlin in my car since i moved to Florida to go to school so my instructor at UTI said he wanted to put it on the dyno and see if he could see anything wrong with it. The car bucks at low rpm under load and also has a stumble at wide open throttle. He said that because of the torque numbers being so erratic that my spark plug wires might be to blame because they are throwing the probes on the spark plug wires off. I also noticed that the car was running at 14.1 a/f ratio under wot so im thinking maybe my stock 140 thousand mile fuel pump cant keep up. What do you guys think. The car also ran worse with the cutout open. Maybe i am fighting two problems and not just one?



car has:
New ac delco optispark
New ac delco plugs
new ac delco o2 sensors
New autolight spark plug wires
new Coil
new ignition control modual
Egr is tuned out of the pcm and all vacum lines capped off but egr is still on intake manifold
Long tube headers
madz28 tune
cutout
new fuel filter
Cleaned maf
newer K&N filter

 

Check the fuel pressure to see how the pump is doing, preferably with a load on the engine. Also check the fuel pressure regulator, pull the vacuum hose of to see if its leaking fuel past the diapram. Make sure the EGR valve isnt leaking vacuum also. With 140k on the clock those valve springs are prolly worn, they are most likely causing valve float also.

 

And i forgot to mention the car is pulling 5-6 degrees timing because of knock when i scanned it the other day. I am thinking maybe that it is running lean (14.1) a/f ratio and then it is detecting knock and then retarding timing causing these problems? I am going to try and get the fuel pressure gauge on it tomorrow and see what i can come up with

 

Damn.... I wish my car dyno'd at 922.62 lb-ft torque.

Its back calculating the torque from the HP and RPM. If the spark is totally erratic, resulting in an apparently instantaneous low RPM, the torque numbers will be meaningless, hence the spikes, and the sudden dips into negative numbers.

Also odd to see a plot with "smoothing" at 0, although that is a way to make the erratic ignition stand out.

The A/F ratio looks too lean.... where did he put the wide-band?

 

900+tq?!?!? damn what rear end you have in that thing to hold that much power?

 

He put the wideband in the right tail pipe. and the cutout was closed except for the last run were it lost 20hp

 

Since you have an ORY you may be OK with the probe in the tailpipe, assuming there's not too much backwash of air. Usually a good idea to put it in place of one of the stock sensors for the pull.

 

Well i got the fuel pressure gauge hooked up and it dose 41 psi at idle and will drop as low as 30 psi under wot in a 3rd gear pull. Is this around normal?

 

The fuel pressure shouldn't drop at all.

 

NO, time for a fuel pump.

 

New fuel pump and after its installed dyno it and send the computer back with the sheet so Ion can tweak it a little. My dyno looked the same when I got a stock base line. My fuel pressure would drop to 20 psi at WOT. Also when the car was hot I would have problems with really bad detonation cause there wasn't enough fuel to help cool the chamber, it would buck uncontrolably.

 

time for a new fuel pump.