1994 1500 4.3 questions

[K85 Octane]

Yo, I'm asking some question for a co-worker since it seems he's getting bad advice from a mechanic about his truck. I'll go over some of the odd things about the truck.

*****Thermal temp reading of the water neck says 200*, but the dash gauge says 160*. I think the temp sender is wrong. Originally I thought the stat was bad. My personal truck reads 190ish*, but it has a 180* stat. There is no way his truck is running 160* and have the water neck surface be 200*.

*****Truck stinks. Really rich and I can smell it driving behind it. I think this might be connected to the temperature sensor. Not sure what temp the "choke" turns off, but if the engine thinks it's 160*, that might cause problems.

*****The exhaust manifold temperature coming straight off the heads reads odd. Driver side is between 400-450*. The temp on the passenger side is 500-550*. The rear cylinders not always being the hottest. The temp was taken ofter coming back from lunch, warm engine @ idle.

*****If you hold a piece of paper or a dollar bill next to the exhaust.....it blows in and out. Not sure what that means, like it's sucking the dollar bill back in. I don't hear any exhaust leaks, so I'm worried.

*****Mechanic told him he has a cylinder down, or warn, or something. He said it was #5, but the exhaust temp doesn't show any difference.

*****The truck uses no water and the exhaust emits no colors or smells of oil. So if there is a problem with a cylinder, it's in the valve seats. I don't believe the engine to use any oil. The oil pressure is remarkable (if you believe the gauge) with ~35-40 @idle and ~55 @highway.


I don't know compression. I know all hoses, belts, alt, spark plugs, wires, cap, and rotor are all new. It doesn't have a lope, but it does seem to have a big hole where it's balls used to be. I drove it some and at one point it had a hiccup or cough and sputtered for a second, then picked back up.

Just wondering if this engine is even worth trying to diagnose. I told him he could slap a 5.7 in there with damn near no modifications.

 

[noJeepshere]

The 4.3 is very nearly the same as the 5.7, just is missing two cylinders. So all the problems with the 5.7 can be translated to the 4.3.

The exhaust leak is is common, as the manifolds are known to warp and sometimes crack. At no load idle it is not discernable, but put a load on it (have buddy set the parking brake, put in gear and rev it some) you'll hear it just fine from the passenger bank.

It does sound like it's misfiring or otherwise has a dead hole. It doesn't even have to be "dead" enough to notice a rough idle or whatnot.

The readings you got from the temp gauge and the water neck indicate what I think is a bad coolant temp sensor. Is the truck TBI or vortec? I understand that the 4.3 had the vortec system before the V8's in some cases. If TBI, it's the one on the driver side cylinder head, vortec is on the water neck (where you were measuring) The computer thinks the engine is cold so is in open loop and dumping gas down the throttle body. That explains the smell and down on power, as well as the possible dead cylinder, as it's fouling the spark plugs.

So basically, your buddy needs to give his truck a tune-up (good stuff, total cost will be around $220) (cap, rotor, wires, plugs) and a new temp sensor. If the cylinder is still dead, the problem is internal.

 

[K85 Octane]

hmmmm that's true about the fouling. Hadn't thought about that. It's been running like that for some time now, so the plugs are probably nasty by now. I replaced the temp sender during our lunch break last week. I haven't heard from him about it yet though, his mind can be all over the place with work/family. It's a TBI setup with the sensor being in the intake manifold. I didn't look for another one, so I hope there's not a second hiding somewhere.

As long as the temp is reading properly now, I'll move forward with a recommendation of new plugs. I think he can hold off on the other stuff since it's still new. (like a couple months new) He picked up a compression tested some time ago but hasn't tried it out yet. I told him do each cylinder one by one and write down what he finds, this way he doesn't mess up wires. Told him how to test it too, as he didn't have a clue.

I'm gonna call him later and bitch him out