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Truck Bogs under Load?

K

klier

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Location
Faribault, Minnesota
Hey!

Of course I'm lusting to be able to spin all 4 of my 33" tires in the mud like all you guys do, but I have a problem you may be able to help me with.

First of all, I've got an '86 Chevy Blazer - NP203 - Chevy 350 - TH350 - Edelbrock Performer Intake - Holley 600 CFM Carb - There are pics at http://kliernetwork.net/truckproject if you want a look

But anyways, I have this lack of power whenever the truck is under load. Hell, it almost seems like the pitch of the engine changes, even at idle, after I try to tug something with it. It is enough bog that it will actually stall the engine. I was thinking it may be an improperly tuned carb, but can you guys give me a list of things to check regarding this problem?

Thanks a lot!

Brian Klier
'88 Camaro 305/TH700R4
'90 GMC S-15 4.3l/TH700R4
'86 Chevy Blazer Hybrid Project 350/TH350/NP203
[email protected]
 
Does it do it without anything hitched up to it? If not you might want to start with the Tork converter and or tranny, and or gearing at the diffs...assuming that the motor runs great with nothing attached to the K5...if you're meaning load like shoving your foot off in it than start with the timing, go to the HEI make sure its working up to specs, if all thats working, check for vaccum leaks, then go to the carb...tape a quarter to the holley throw it away, and go get a Quadrajet...and when someone finds the holley they've got a quarter
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Good Luck and I'm sure they will be others with long lists also!!!
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And lastly if you want all 4 tires to show rooster tails better get good lockers or spool the diffs!!!!!


<font color=blue> White Knight</font color=blue>
 
Thanks for the response!

Yeah by load I mean just making the engine work more than it would on a flat asphalt road for example. Yes, I was actually pulling a trailer in 2 foot high wet grass at the time, but i can duplicate this problem every once in a while by just speed braking too. Once the engine gets in this "mode" it is like it loses half of its power. Eventually after about 15 minutes or so it will go back to normal - kind of hard to explain. The idle will still be strange in that "mode" even with the tranny in park, so I highly doubt it's driveline related.

Seems to run very well on of them there flat roads though, but thats not exactly what a 4x4 is for now is it? :-) I may just take your advice on the Holley if all else fails here. I only paid $50 for the thing anyways...

Brian
 
Check the fuel flow....is it electric or mechanically driven...and again toss the holley!!!!
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<font color=blue>White Knight</font color=blue>
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I have a mechanical fuel pump on there.

I spent a little time today thinking back at all the times this "strange idle" started happening, and there seems to be a few commonalities...

1. Usually after I drive a long distance, like 3+ miles and the engine gets warm.

2. After I shut off the engine and let it sit (heat soak), then I seem to have this strange idle problem at the next startup until that heat bleeds off.

There is no heat shields on these exhaust manifolds, and it does get pretty warm. The spark plug wires, especially number 8, seems to be pretty hot to the touch (near the spark plug end). Is this heat somehow causing the wires to misfire causing this missing/strange idle?

Brian
 
It's got a Holley with an electric choke. The Choke plate is fully open (vertical) every time I have looked...

Brian
 
Brain- Your last post sounds really familiar to me- I had a similar problem a few years back, and it ended up being a weak diaphragm in the mechanical fuel pump. As soon as it got warm, my performance dropped, and occasionally would be really hard to start if I shut it off, ran into the store for a few minutes, and then tried to fire her up again.

A friend suggested I eliminate the mechanical pump, so I swapped it for an electrical pump back by the tank. I haven't had a reocurrence, and I gained some power to boot!!

I would also recommend checking the fuel filters, and something tells me you might want to check your ignition module- heat can cause those little buggers to act up, too!!Most auto parts places have a free module testing available.
 
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