Some driveability issues.

[VetteMed]

I've been driving the Z a lot these past 2 weeks (just about to roll over 191K miles), and I've noticed some consistent issues, I'm hoping someone may have some idea of where to start looking.

My daily commute has been about 2 hours each way for the last 2 weeks -- when I get about 45-50 minutes in to the trip, the idle begins to hunt up and down, by 200-300 rpm. It acts like a vacuum leak, but I'd expect a vacuum leak to be worse when cold, and improve when warm, as the metal parts expand.

Another issue I've noticed, and this also seems to not be an issue until the engine is fully warmed up, 40-50 minutes in to the trip, is that I get a bog / hesitation when rolling on to the throttle in a corner. Gentle sweeping turns in the road are not an issue, but an actual corner, taken at 20-30 mph, while in gear (usually 3rd or 4th), results in a complete loss of engine power, a bogging/hestitation sensation. As soon as I straighten out after the corner, power returns to normal and it runs fine.

Background info:
1991, 191K miles
Mostly stock, except for Jeal Headers, no cats, FIC injectors, secondary throttle plates removed, Haibeck PROM, 93-95 Injector housings.
Power seems to be excellent, fuel mileage as well (21-23 mpg).

Thanks,
Andrew

[lbszr]

For the power loss in turns, could connect a fuel pressure guage and see if it drops off in the turns to see if there's an issure in the tank. There's a sump in the bottom of the tank to prevent fuel starvation.

Sounds like you need to detune it anyway, since the cops are eyeballing you

[VetteMed]

Originally Posted by lbszr

For the power loss in turns, could connect a fuel pressure guage and see if it drops off in the turns to see if there's an issure in the tank. There's a sump in the bottom of the tank to prevent fuel starvation.

Sounds like you need to detune it anyway, since the cops are eyeballing you

I thought of the fuel pump issue too, but this has been happening even on a tank that's close to full, so starvation seems impossible in my mind. I don't know if my fuel pressure gauge can reach to the windshield while connected.. but I'll give it a try.

You're probably right on the cop issue

[XfireZ51]

Originally Posted by VetteMed

I thought of the fuel pump issue too, but this has been happening even on a tank that's close to full, so starvation seems impossible in my mind. I don't know if my fuel pressure gauge can reach to the windshield while connected.. but I'll give it a try.

You're probably right on the cop issue

You are starving fuel because of filter. Likely the sock filter on the pumps.

[VetteMed]

Originally Posted by XfireZ51

You are starving fuel because of filter. Likely the sock filter on the pumps.

Why is it only appearing on turns? If there's enough fuel in the tank for the pumps to be completely submerged, why would it have good performance in s a straight line? I certainly don't mind pulling the pumps and inspecting/replacing the strainers, but it just seems odd.

[XfireZ51]

The filter socks are what control the amount of fuel surrounding the fuel pump inlet. If the sock is clogged it let's in only
so much fuel at any time. In a turn the fuel may slosh to one side of the sock because there may not be enough to
completely fill the sock.

[VetteMed]

Pulled the fuel pumps out today, and changed the strainers. There was honestly no sign of anything wrong with the ones that were on there.

[VetteMed]

I checked for codes this morning, had a stored low TPS code (22), I checked the voltage at closed throttle, it's within spec (0.53v), so I'm going to replace the TPS and see if that improves the driveability issue.

[VetteMed]

Update: After finally getting the Z back on the road, it appears that changing the TPS has eliminated the driveability issues that I was experiencing. There's no more of the cutting-out while in a corner, the hunting idle is about 95% improved, and the light-throttle cruise is much smoother. Just wanted to post up in case anyone has similar issues in the future.