Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
1997 chevy misfires at high speeds
2 months 2 days ago #64771
by Gageb562
1997 chevy misfires at high speeds was created by Gageb562
I have a mystery misfire on my 1997 2 door tahoe witht the 5.7l vortec v8. It drives great on the streets, no hesitation in the throttle, lots of power and no signs of a misfire. As soon as I get up to 60+ mph on the freeway, it will start misfiring on cylinder 6, shaking the whole truck and throws a P0306 and P0300 code. It will then slip the TC so I can't get it into full lock or else it will just keep misfiring under load (especially when towing). I have a TopDon scanner tool that I used to set the camshaft posting retard when I installed a new distributor ( gear was pretty worn). I've also replaced cap and rotor 3 times, ignition coil 2 times, ignition coil control module 2 times, plug wires, all 8 spark plugs, fuel filter, crankshaft position sensor, transmission speed sensor, and both upstream 02 sensors. It still rides great on the streets, but nothing made my misfire on cylinder 6 at 60+ mph go away. When I tested the fuel pressure I get about 55 psi KOEO and about 48 psi at idle. I thought the fuel pump was okay because when I'm driving through gears the psi is a constant 60 psi, even when it's misfiring. I'm thinking about just replacing the fuel pump but I'm tired of firing the parts cannon at my beautiful truck. Oh yeah, MAF and O2 sensors all check out and fuel trims are normal and I upgraded the injector to the electronic spider about 5 years ago. Any help would be much appreciated.
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2 months 1 day ago #64782
by bills4065
Replied by bills4065 on topic 1997 chevy misfires at high speeds
I did not see if you have done a compression check yet on the engine.
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2 months 1 day ago #64783
by Gageb562
Replied by Gageb562 on topic 1997 chevy misfires at high speeds
I have only done a compression test on cylinder 6 and I got 155 psi. I will do all 8 cylinders tomorrow and I'll let you know what I get.
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2 months 18 hours ago #64798
by Lupe
Replied by Lupe on topic 1997 chevy misfires at high speeds
you said the gear on distributor was worn , might want to look into hole and check your cam gear that it sit in .
good luck
good luck
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- ontheriver
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2 months 12 hours ago #64804
by ontheriver
Replied by ontheriver on topic 1997 chevy misfires at high speeds
What about a inspection of the valve springs, might have a cracked/broken one on that cylinder?
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2 months 11 hours ago #64805
by Gageb562
Replied by Gageb562 on topic 1997 chevy misfires at high speeds
I pulled the vavle cover off just to see, and everything looked good.
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2 months 9 hours ago #64806
by Gageb562
Replied by Gageb562 on topic 1997 chevy misfires at high speeds
Compression test (dry):
1: 190 psi. 2: 175 psi
3: 190 psi. 4: 175 psi
5: 175 psi. 6: 175 psi
7: 195 psi. 8: 150 psi
1: 190 psi. 2: 175 psi
3: 190 psi. 4: 175 psi
5: 175 psi. 6: 175 psi
7: 195 psi. 8: 150 psi
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- Hardtopdr2
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2 months 8 hours ago #64807
by Hardtopdr2
Replied by Hardtopdr2 on topic 1997 chevy misfires at high speeds
You will want to test valve spring tension and look at push rod ends for that cylinder. this will determine if you have a valve floating from weak valve springs or a collapsing lifter\bent pushrod. also check and readjust rocker arms.
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