90 GP Lacks Power

Chavo2005 · #1 12-02-2003, 10:16 PM

I have a 1990 GP LE that lacks power and has very poor gas milage (about 230 miles per tank). Since we have had the car, got it in November of 2002, we have replaced the plugs and wires, EGR, Alternator, TPS, MAP sensor, PCV valve.. Nothing seems to help. It has had a rough idle, the car would vibrate bad, the Tach didn't show any RPM drops or anything tho. Also when I mean lacks power, the acceleration is horrible. At full throttle the car goes 0-60 in approx. 13 sec. if not more than that. My dad has a car with the same engine and trans. and has way better performance than this! Recenetly when the car was started it would start then shut back off. Now you have to depress the accelerator a bit to get the car running and to just idle. when you take your foot off, it dies. Only option i had was to adjust the idle screw until it was all the way in just to keep it running so i don't have to be in the car. May i mention no SES light or codes since i replaced the TPS and EGR. Could someone please give me some suggestions on what to do next. Also i was thinking it may have a bad Engine Control Computer. Thanks

Ripn12s · #2 12-03-2003, 04:48 AM

Sounds like it could be a fuel delivery issue????? Bad pump, injectors, fuel filter???????????

Tim

The Burning Rom · #3 12-04-2003, 10:48 AM

The ECU could be bad.

Have you tried performing and idle re-learn on it since you replaced the TPS?

Chavo2005 · #4 12-04-2003, 06:42 PM

i tried the idle relearn teqnique found at http://www.60degreev6.com/index.php?p=pages&pid=74 , also be for hand i put the idle screw back to its approximate original position. The car turned over and attempted to start several time but failed. I tried for a couple min, with no luck. i then gave up cause the bat. was running kind of low and push down the accelerator and got it started that way (Had to push it all the way to the floor) but it eventually started. AS sugested before it may be a fuel system issue, seems to me that it is the fuel pump. An sugestions on how to test this?

radeohedca · #5 12-05-2003, 08:10 AM

The last time I had a car with those symptoms ...rough idle, no power & poor fuel economy... I ended up having to change the cam shaft.

I discovered this one day as a consequence of attempting to quiet a noisy valvetrain by removing the valve covers to adjust the slop in the lifters. With the car running, I noticed that some of the rockers where not moving much. Sure enough when I took the old cam out and had a good look at it, some of the lobes were almost round. While I was at it, I changed the lifters and timing chain/gears. Of course, the car ran markedly better after I changed the cam.

The degradation was very gradual so it never hit me until it got really bad (it wasn't a sudden change). It was an '82 Z28 with a 305 engine. Apparently it was a common problem due to a poorly hardened batch of cams in 305's from that era. I suspect this could also be caused by not changing your oil often enough and eventualy show up in an engine with high miles.

This may or may not be your problem but it's worth investigating.
Cheers, Hugh.

The Burning Rom · #6 12-05-2003, 11:31 AM

While Hugh's suggestion does make sense, I've NEVER heard of it happening on a GEN II 60* motor.

As far as the fuel system test, you will need a fuel pressure gauge. There is a test port on the end of the fuel rail that you can connect it to.

kilroypr · #7 12-10-2003, 10:26 PM

Well, I agree with ROM. Check the preassure. You should have a fuel deliver problem. Most probably the fuel filter cloged. Also change the air filter.
Intake Air and Fuel Filter are first cause of hesitation, poor performance.
If the fuel presuure is above 75 then check that the throtle body is clean and that all the intake(fuel and air) are clean as well

Chavo2005 · #8 12-26-2003, 12:59 AM

today when i went to start the car to check the fuel pressure, as i have been very busy and had not had time to do it, it would no longer start. it would turn over but not fire. there is pressure at the fuel rail so it is getting fuel to this point. i checked for spark and there isn't any, i also check the exhaust for gas fumes, none. so no spark, and no injector pulse...does that mean a dead ECM? i had started the car a couple of days before this to circulate the oil and keep the charge in the battery. i also check for codes and it still shows 12, which means nothing important!

kilroypr · #9 12-26-2003, 01:17 AM

Chavo, with a scanner you can determine if the injectors are actuating or not. Definetly if the 6 sparks are not firing then I could not say is the module could be more like the crank position sensor or the PCM(ECU, ENgine Control Unit) going north.

Chavo2005 · #10 12-26-2003, 04:51 PM

ok i believe it was the crank position sensor, it was broke when i went to remove it, but there is a piece sill in the engine, how do i get it out?

kilroypr · #11 12-27-2003, 02:39 AM

Rom, Ripn12s any clues of getting out the CAM possition sensor?

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