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97 Jimmy runs like dog do


highhopesforcars
04-10-2008, 02:05 PM
OK my 97 with 103K on i have changed 2 Os sensors right where the y pipe meets the cat i still get an O2 fault oonce inawhile usually right after it has one of its episodes. This consist of sitting at a light and the idle dropping 2 to 3 hunred RPM wanting to stall but doesnt then it jump back to life after 5 to 10 seconds. It is also hard to start takes up to 45 seconds of cranking sometimes i have to stop cranking and do it again and another 10 seconds or so to start. Off idle it runs real strong. I was wondering if it is a timing issue my MT2500 says the cam sensor is at -5 to -6 degrees all the time i figured it should be near or at 0.

highhopesforcars
04-17-2008, 11:46 AM
OK i checked the fuel pressure key on engine off its 60 PSI engien running 50-54 pst is bounces alot. turned key off watched gauge drop from 60 psi to 40 psi in 10 min.changed coolant due to it looks like someone took a dump in the radiator.Idles at 900 in neutral and 550 in gear.if i adjust the distrubtior will that affect my cam timeing to help the idle and for the fuel pressure dropping off what would be the problem and ow to trouble shoot. I was thinking check valve. but what about pressure regulator or leakign injectors?

MT-2500
04-17-2008, 12:09 PM
If a 4.3 engine
Fuel pressure is to low.
Camshaft retard does need to be as close to 0 degrees as you can get it.
Is your dist adjustable or a fixed hold down clamp?
Test pump out first to make sure it is not weak.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

highhopesforcars
04-18-2008, 06:50 AM
Ok last night i hooked the fuel pressure gauge. this morning 25 psi with out even touching the key. then it slowly came up to about 60 while cranking. Going down the road i maintain about 56 psi. When i get on it I get around 60 psi at full throttle. When i stop at a light it drops to 54 again. I blocked off the return line only got upto about 65 psi. I assume its the fuel pump it bad

MT-2500
04-18-2008, 08:37 AM
Ok last night i hooked the fuel pressure gauge. this morning 25 psi with out even touching the key. then it slowly came up to about 60 while cranking. Going down the road i maintain about 56 psi. When i get on it I get around 60 psi at full throttle. When i stop at a light it drops to 54 again. I blocked off the return line only got upto about 65 psi. I assume its the fuel pump it bad


Maybe.
You could also have pressure leakage at fuel pressure regulator or injector body.
To make sure it is weak fuel pump.
Check the direct fuel pump pressure at pressure line from fuel pump to fuel filter.

MT

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