Engine light comes on only at hwy speeds?
Thread Starter
Member
Joined: Sep 2010
Posts: 120
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From: Angleton, TX. Third Coast
Car: 88 T/A. TOTALLED!! (not by me)
Engine: TPI 5.0
Transmission: 700r4 Auto
Axle/Gears: 2.73 posi
Engine light comes on only at hwy speeds?
When driving under 65-75 mph the light never turns on , but when on the highway, cruising to the next town (about 10 miles away) at ~70-75mph the light will come on. After the car is driven at slower speeds for a while, or parked and turned off and then re-started, the light will go off and doesn't come back on until the car is driven at highway speeds again. Car is running fine, coolant level and temp is good, battery voltage is good, oil pressure is good, etc. Any ideas what could cause this issue?
Thanks,
John C.
Thanks,
John C.
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Joined: Jul 1999
Posts: 17,262
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: Engine light comes on only at hwy speeds?
Get a flash code. Best guess is the o2 sensor but that's throwing a dart at a board withing having some diagnostic information.
Junior Member
Joined: Dec 2004
Posts: 84
Likes: 1
Re: Engine light comes on only at hwy speeds?
When driving under 65-75 mph the light never turns on , but when on the highway, cruising to the next town (about 10 miles away) at ~70-75mph the light will come on. After the car is driven at slower speeds for a while, or parked and turned off and then re-started, the light will go off and doesn't come back on until the car is driven at highway speeds again. Car is running fine, coolant level and temp is good, battery voltage is good, oil pressure is good, etc. Any ideas what could cause this issue?
Thanks,
John C.
Thanks,
John C.
I drove 1600 miles straight through to East Texas with the stock 195 thermostat and the damn light came on after every stop. I drove back with the 180 thermostat and never saw the light.
Senior Member
Joined: Oct 2011
Posts: 638
Likes: 0
From: Chicagoland area
Car: 1986 Z28
Engine: ZZ3
Re: Engine light comes on only at hwy speeds?
I'm going to bet it's the ol' EGR code thing. There was a thread around here some where about EGR temperature or some such thing. It's been a while I don't remember exactly.
Joined: Aug 2011
Posts: 661
Likes: 7
From: Texas
Car: 91 Firebird/88 Firebird/91 Formula
Engine: V6 3.1/V8 5.0/V8 5.0
Transmission: 4L60/700R4/4L60
Axle/Gears: 3.23/2.73/2.73
Re: Engine light comes on only at hwy speeds?
My 88 was doing this when I got it in April this year. EGR wouldn't hold vacuum. Replaced the EGR and haven't had a light come on since. But it was throwing the EGR code.
Thread Starter
Member
Joined: Sep 2010
Posts: 120
Likes: 0
From: Angleton, TX. Third Coast
Car: 88 T/A. TOTALLED!! (not by me)
Engine: TPI 5.0
Transmission: 700r4 Auto
Axle/Gears: 2.73 posi
Re: Engine light comes on only at hwy speeds?
Ok, so where can I find info here that tells how to pull the codes? And does the light have to be still on, or will it be stored? It's OBD1 right? Don't think the prob is temp related because the car runs pretty cool as long it's not putting around or idling a lot. Could be tho. Car has 135K+ miles, and I don't know if the o2 sensor(s) have ever been replaced so ti could be that too. If it's egr can I just remove it (egr valve) and block it off? Car doesn't have to pass smog anymore here and has no catalytic and a 3" flowmaster cat-back as its only mods. Otherwise it's stock.
Thanks
John C.
Thanks
John C.
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From: Mile High Country !!!
Car: 1967 Camaro, 91 z28
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