My car is running like crap. I recently did a tune up on it, and ever since then, it hasnt run right. I also replaced the TPS sensor because the old one had a flat spot in it. But, the car still runs rough. Do you need to adjust timing after a tune-up??? Heres what it seems to do. When you first start it, it runs GREAT, no missing, or cutting out. Then after the t-stat opens and the engine is at normal temp., it cuts out about 2000rpm or above. If you drive it easy, its ok, it just does this under a load. It also idles rough after its warm. I tried injector cleaner also, thinking it may be fuel related. BUT, wouldnt it do that ALL the time, not just when its warm??? Would a bad O2 sensor do this?? Or possibly the coolant bypass is messing with the timing?? Any ideas would be greatly appreciated......By the way, I love this site...

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1991 Z28 5.7tpi stock except for 3in flowmaster exhaust with 2 high flow cats, and the tb coolant bypass.

 

did you adjust the TPS to factory specs?

Curtis

 

Coolant bypass shouldn't mess with anything at all. When you do a full tune up, timing should be checked, but unless you removed the entire distributor, it shouldn't have changed, unless you changed it. As far as your drivability problems, I'd suggest running the car with a scanner hooked up, if you have one, or know someone who does, or run the car in field service mode and check to see whether or not the SES light flashes towards the lean or rich side. I think if you're under load, it should be more toward the rich side. I'm not positive the field service mode can give you info while you're accelerating, or just when idling, but it's worth a try.

 

my car is doing the same. i have a a/f ratio gauge and its going lean. most of the time off the scale. my car has a bad flat spot about 1/2 throttle.

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92 z28 170,000 miles 14.20 on goodyear eagles before exhaust only mods k&n and slp 13/4 headers and dual 2 1/2 exhaust
87 trans am 12.20 on motor too many mods to list

 

Since the problem started after your tune up it would make sense that the problem is with the TPS. What did you adjust the voltage to on the TPS? It needs to be at 0.54 Volts +/-0.075 Volts.

Did you disconnect the battery cable to clear the computer memory after the TPS swap. The computer would still think you have the old one on there if you didn't.

Since it is running bad after it has warmed up, it could also be the O2 sensor giving false readings to the ECM. With those false readings the ECM has learned an incorrect fuel and spark map to go by during normal and WOT driving. It just wouldn't show up as bad under light throttle as you had mentioned.

It would not be the coolant bypass.



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89 IROC-Z 5.7L
130,000 MILES
2.77 GEARS
K&Ns FILTERS
ALL FREE MODS
FLOWMASTER MUFFLER
PERFORMANCE RESOURCE CHIP
Best 1/4 E.T. 14.37 @ 95 MPH
Best 1/8 E.T. 9.22 @ 76 MPH
Best 60ft. 2.07

 

How Do you adjust the Voltage on the TPS sensor??? I readjusted the timing today, its alot smoother. My friend said it could be a bad plug possibly. Im using Bosch Platinums. My 96 camaro I had did the same thing sortof after installing the Platinum +4's. I didnt overtighten them, Im sure of that, just got'em kinda snug....I have picked up a slight exhaust "tick" which Im hoping is just a leak.(I will find out tomorrow) I was also thinking it was the 02 sensor, BUT wouldnt that throw a code on the computer??? I did reset the computer after the TPS switch and today after adjusting the timing. It has smoothed out some, but still feels like its detonating or cutting out around 2200-2500rpm at hard throttle. Any more ideas...?????

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1991 Z28 5.7tpi stock except for 3in flowmaster exhaust with 2 high flow cats, and the tb coolant bypass.

 

As long as you used a TPS for a '90-'92 TPI car, you do not need to adjust (actually, there isn't really any adjustment...other than a little slop in the mounting holes).

The SD TPI's use the TPS voltage at startup as the idle TPS setting.

 

I fixed it.....(thank god). You wont believe this, but the plugs came loose. When I put them in I got them snug and then I tightened them another 1/4 turn. BUT, I thought I might have a bad one, so I bought some Rapidfires today and changed out the Bosch Platinums. The first one (cyl #1) came out with just my hand loosening it....Weird huh?? Oh well, I replaced all of them and reset my timing again to 6 deg. at idle in drive, and 30 deg. advanced at 3000rpm. It runs awesome now. Thanks for all the help though. Im going to have the engine tore down this winter in preparation for a 383 stroker, so Im sure Ill be full of questions...... And finally, does anyone know where I could find some Vette L98 heads(aluminum)??? And possibly some used headers?? Thanks in advance..


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1991 Z28 5.7tpi stock except for 3in flowmaster exhaust with 2 high flow cats, and the tb coolant bypass.

 

I've seen heads on ebay every now and again... also check the clasified adds here as well...

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91 z28 lb9 5 speed - hooker 1 5/8 headers - high flow cat- full 3 inch exhaust - home made ram air - tpis airfoil - dual chamber flowmaster - Stage 2 Jet Chip and 160 stat - 8 mm Msd plug wires - 55,000 v hypertech coil/rotor/distrib. cap - Mac. White face gauges - lots of sound system crap...

 

Mike is right, you do not adjust the TPS on SD cars. If you want to alter the point PE (WOT) kicks in, you adjust it inside the prom itself. You can make PE engage at any %TPS vs RPM you desire inside the prom.