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post #1 of (permalink) Old 04-08-2003, 11:06 PM
jeeper131
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wierd problem at 74 mph? thumpity thumpity

Greetings all, I was hoping to get some advice about a stumper of a problem I'm having. I drive a 93 S-10 2WD pickup with the 2.8 TBI, manual tranny w/ AC. Its got 84k on it and I keep up with the maintenance as best as I can, regular oil changes and all that. Its a far cry from the super-truck I figured I'd be driving by now, but its also never really given me any problems despite its hard use. Here are the symptoms:

On long drives, usually over a 100 miles, It'll start out just fine and I'll get up to about 74-76 mph cruising speed. After a random time, (sometimes an hour and a half, sometimes 2 or more) into the drive the engine will start to hesitate and thump. It'll keep it up and lose power as long as I keep my foot down and stay in 5th. If I shift into 4th and continue at a lower speed, around 60 say, it'll go away. After that It'll run like an absolute pig and be almost impossible to get up to decent highway speeds again. Also, I get crap gas mileage, around 15, when I usually got around 22 or so. I know the following things. The thumping is the engine backfiring up through the throttle boddy. I know this becuase when i looked under the hood the aircleaner cover was blasted off center. I changed the fuel filter, as well as most of the ignition components about 2 monthes ago to try and remedy the problem, to no avail. The thumping funness starts at pretty random times, but only at highway speeds after a while, around town it drives just fine. I've had peopel suggest that its the fuel pump, or even a clogged catylitic converter. I'm open to suggestions, and any advice would be appreciated. Thanks

Mark
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post #2 of (permalink) Old 04-08-2003, 11:21 PM
 
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Re: wierd problem at 74 mph? thumpity thumpity

A clogged cat would give you no power at all. Like 2500 RPM uphill in second gear no power.

Sounds like you're getting too much fuel or too much pre-detonation at higher speeds. Is the timing true on it? Fouling of the plugs of any type?
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post #3 of (permalink) Old 04-09-2003, 09:54 PM
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Re: wierd problem at 74 mph? thumpity thumpity

I'm thinking dist or valves
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post #4 of (permalink) Old 04-09-2003, 10:53 PM
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Re: wierd problem at 74 mph? thumpity thumpity

i just replaced the distributor cap, but wouldn't a messed up distributor cause problems at all rpms and not just at random? How much does this sound like a fuel pump on its way out? [img]images/graemlins/puke.gif[/img]
post #5 of (permalink) Old 04-09-2003, 10:54 PM
 
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Re: wierd problem at 74 mph? thumpity thumpity



Hey,

The only thing that will usually make an engine backfire thru the intake is incorrect timing or a sticking lifter / valve.
The timing is usually right or wrong, and in this case, it's hard to say one way or the other. It is possible that the magnetic pickup inside the distributor is fouled or damaged, or that the ignition module may be going out (the ignition module is adversely affected by heat retained in the block, intake, and even the distributor casing itself. One question -- Does the truck start and run good after sitting for half an hour or so? If it does, the ignition module is a probable culprit.


On the other hand, if you have a valve lifter that is gummed up intermally, it may stick as the encine heats up.

Offer up a little more info, and we'll try to help some more.

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post #6 of (permalink) Old 04-10-2003, 12:25 AM
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Re: wierd problem at 74 mph? thumpity thumpity

i have a 86 s-10 blazer 2.8 with automatic transmission and i had it do the same thing back in november when i driving back to school. since then we have had the head rebuild becasue the engine has over 230000 miles on it it then seemed to be a chain effect from there it just wouldn't run right no matter what we did. we checked the timing and it was off by a tooth the timing chain was loose and the top gear was warn down and it had jumped the timing. but that didn't solve the problem but i was a factor. we changed the pickup coil thinking that might make a difference but no change. the next thing we are going to look at is having the proms on the ecm reprogramed or replace them. we have pretty much narrowed the problem now down to either the wiring, a prom or the ecm its self.
i hope this helps some PM if you have any questions about anything else
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post #7 of (permalink) Old 04-10-2003, 12:35 AM
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Re: wierd problem at 74 mph? thumpity thumpity

Sometimes a bad PCV or EGR valve will do that too. I swapped in new units for both and my hack & sputter went away on my 88 4.3
post #8 of (permalink) Old 04-10-2003, 12:38 AM
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Re: wierd problem at 74 mph? thumpity thumpity

whe my egr was pluged on my 94 4.3 it only wanted to sputter and try to stall at slow and idle speeds, but that would be good to check
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post #9 of (permalink) Old 04-10-2003, 07:59 AM
 
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Re: wierd problem at 74 mph? thumpity thumpity

My money is on a deteriorating catalytic converter.
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