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Hestitating and stumbling on '86 K5 Blazer...

Hey all...

My mechanic buddy is out for the weekend, thought I'd check here.

My Blazer (5.0L) starts up and idles just fine. When I take off from a dead stop it hesitates/bogs down for a second. It doesn't really pick back up and it usually involves some fancy footwork on the accelerator to get it going. A couple of times it's died.

Also, I'll be driving down the road, and it starts stumbling, like it's out of gas. I can pump on the gas, and it'll keep moving, but the problem doesn't seem to be solved, rather it just clears up.

And it's occasionally running hotter with the A/C blowing. Hotter than it did last summer. Overall, there is much less power, and much more fuel consumption. A week of driving to work and back would leave me with extra gas, but now I'm barely making it 4 days without another fillup.

As I type, it's cooling down, and I'm about to replace the fuel filter. I priced a fuel pump--chump change... but if the filter isn't a problem I was gonna change the pump. This truck has 156,000 miles on it. It was a Police truck, so one would assume the maintenance on it was pretty good. But I don't have a list of what was done and when. I'm strictly a wrench turner. I'm not the best at diagnosing these things on my own, and I don't want to replace parts until I find the problem. But it seems fuel related...

FYI, folks have been throwing suggestions at me. Someone said head gasket. The truck isn't losing coolant or oil, and when I changed the oil last week there was no sign of coolant in there. No leaks around the heads that I can see. And again, it idles just fine. Most head gasket related problems I've seen were causing much more serious symptoms. And the stumbling I'm experiencing isn't consistent. Most head gasket issues I've seen were not intermittent.

I was told to check the catalytic converter... that doesn't seem to be an issue, and I've consulted 3 muffler shops who said (based on my troubles) that the cat wasn't the culprit, and furthermore that they would NOT take my money and replace the thing.

Any and all suggestions would be greatly appreciated.

Thanks,

-JP

Reply to
Jon R. Pickens
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Your're missing the blatantly obvious. It has poor performance and increased fuel consumption. It's running rich. Assuming it has good plugs, wires cap and rotor + correct ignition timing, on a carbeurated motor, the only thing that causes this is the carb being out of adjustment or a float bowl problem. It's not the fuel filter, as you have TOO much fuel, not too LITTLE fuel. Could also be the choke pull-off is gone and the choke it stuck closed. There is a slight chance it's the EGR valve, but I doubt it. Could also be the timing chain is nearing the end of it's life.

I'm guessing Rochester Quadrajet right?

First, check to make sure the choke is opening all the way when it's warmed up. If it isn't, it could either be the pull-off (heated electric element) or the vacuum pot is not holding vacuum.

If the choke is opening up ok, check the mixture screws. There is one for each primary barrel on the front of the carb. Clockwise is to richen the mixture, counterclockwise is to lean out the mixture. Give 1/2 to 1 turn in the lean direction and see if this clears anything up. Wouldn't hurt to open the carb up and check the float as well.

HTH,

Doc

Reply to
"Doc"

Doc,

I was advised to go ahead w/ the fuel filter, plug the vacuum line coming off the EGR valve, and cut a tiny hole in the hose coming off the front of the carb that goes into the cannister up behind the drivers side headlight--to let it vent properly.

I did this, and now the truck runs great. I took it for a spin along a route that had several stop signs (to test takeoff from a dead stop) and then brings me back home on a long stretch of uninterrupted highway (to test the surging at normal driving speed). Both issues appear to be gone. Neither had been better or worse with a cold or hot engine.

Also, I was out for about an hour, and the gas needle barely budged.

I was told that if it was running rich, I'd have more soot build-up in the tailpipe, and that I'd notice more smoke from the pipes under harder acceleration or going up hills. I noticed neither when I checked.

I checked the choke, looked good (had done this not so long ago as well when I was having other troubles).

If I notice any more problems, your suggestions will be the next on the list.

Thanks,

-JP

Reply to
Jon R. Pickens

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