Hi All..

Well I finally resolved my fuel pressure issues.. Turned out to be a bad fuel pump and a bad regulator what a pain. The car now has 38lbs pressure at idle and 48 lbs at WOT (vac line disconected).

So Ive now got 4 (hopefully)minor problems. Im hoping the experts here can give me somewhere to start. Ive read the service manual and wasnt able to get much out of it in the way of direction. Here are the problems:

1. Under WOT (with a load) the engine has very little power. When I back off the throttle to 3/4 the car takes off lots of power. The engine seems to run ok under WOT but just does not 'rev up'. Backing off a bit it seems to run ok. I just changed the plugs and did a visual on the wires, they seem ok. The service manual says to chack timing, but I thought that the timing was all handled through the ECU?

2. At idle the RPMs seem to surge a bit. The RPMS will slowly drop a few hundred rpm and then kick back up. This process takes about 20-30 seconds.

3. When pulling up to a stop sign, the engines RPM will drop dramaticly, then downshift to first and then come back up a bit. The problem that Im having is that the rpms drop so much that the car almost dies. Ive read somewhere that this is normal for L98 engines but Im concerened that the rpms are dropping to much.

4. When accelerating from a stop, the engine seems to stumble a bit just off of idle. I can give it more gas to get it out of this stumbling mode, but it gets anoying after awhile. This also happens when the car is not under load (ie: in neutral) but isnt very noticable.

My assumption is that most of these problems are related to each other in some way, or at least thats my hope! Well, at least I can drive the car now!

Thanks everyone for the help!
Joe

 

I'm sure you have probably done this if you changed to fuel pump..but did you replace the fuel filter? S clogged fuel filter can cause stumbling problems like you are describing.

 

Yea.. I wish it was that easy :0 The filter was the first thing I changed

Joe

 

have you checked the tps?? that would certainly explain why the problem is worse at some rpms than others

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89 Iroc-Z LB9 305 TPI auto 2.73 posi:
3" Dynomax "cat" back,K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, 180' thermo, mild ignition mods, synthetic oil, kicker sound system, soon to attempt engine swap...

 

Any clues on what to look for when inspecting the TPS? Visually it looks fine..

 

Ya the timing is handled by the ECU, but you have to set the base timing at the distributer. You also have to adjust the TPS voltage. While you are at it you sould also adjust the IAC.

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86 IROC T5
MSD 6A
Summit cam
Flowmaster
AFPR
Lowered 1.5"
My own prom (finally)

 

If your car is stock you might be running rich with the higher fuel pressure,no sig,no info on the car it's a guess

 

Ok.. I checked the TPS and it seems fine. .65 volts at idle and 4.35 at full throttle. It smoothly increases as throttle is opened.

Anyone know a way to check the IAC?

Joe

 

in the tech articles there is directions for this and the tps.

Jeremy

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92 Z conv
5-spd B&M shifter
home-made ram air, air foil, headers, no cat, TB bypass, kevlar pads, slotted rotors, BMR panhard, alston SFC
when it warms up Edelbrock STB maybe springs