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Motor or trans; which one is broken?

cabledawg

cabledawg

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A little back history: 90 GMC Burb with a swapped in SM465/205 and a 350TBI. Roughly 250k (speedo/odo broke 6 years ago) miles on the truck, dont know how many on the engine/trans.

Up until now, this truck has been my reliable one. Maybe a snafu here or there (like starters, thermostats, etc), but never anything major once I put in the SM465. But the other day after a few minutes of driving, she kinda sputtered like it wasnt getting fuel. I pushed in the clutch, she idled out smooth and I drove off with no issues. This morning though, started out the same (same intersection as last time) but now I couldnt get past second gear without the engine sputtering. BY the time I got to work, i couldnt accelerate without the engine sputtering. Push in the clutch though, and she runs fine. I did notice yesterday that the AF is really mucky so I'm sure a head gasket is blown, but the oil looked fine. I havent checked the trans for damage but ti'll be on my list of things to check later today.

I've got a NA 6.2 coming to swap in later this year, but I'm wondering how long the 350 is going to last. It's old and needs a rebuild, but if there is a simple fix to get me by for a few months, I'd rather do that instead.

One more thing, our weather has been crazy up here. Low 40's during the day, 20's at night with the occasional snow storm. Half tank of gas, could it be moisture causing the sputtering? :dunno:
 
I had a jetta that did that because of a cracked coil. If moisture is getting into a small crack it can cause that.

you can try spraying down the distibutor cap and plug wires with wd40, it might help and couldn't hurt.
 
I've had a few distributor caps and rotors that let spark jump thru them to ground while the engine was under a load,like when first taking off when you release the clutch,I'd have to push it back in,let the engine rev up and recover,then try again,and it would buck and sputter until it got up to speed...replacing the rotor fixed the problem on one vehicle,the other the cap and rotor looked old and possibly cracked so I replaced them,and the problem vanished........................................................................................................A pick up coil in an HEI can cause similar symptoms when the wires get broken from the vacuum advance moving them back and forth constantly for thousands of hours--it can cause an interuption in the spark when the advance kicks in..fuel starvation or contamination can also cause this ,check for low pump output or a clogged gas filter,water in the fuel,etc..
 
More driving today revealed that when the engine is cold, it seems to run fine, but once it warms up, there's no power beyond idle. Unless I'm easy, and I mean real easy, on the gas, the engine will jump and sputter while driving. In neutral, I can rev the engine and its fine, but under load its rough.

I'll check the plugs/wires/dizzy/coil. Its a TBI so there isnt a vacuum advance, no worries there. The plugs havent been changed since 2005, wires since about 2006, the coil since 2008, and I've never touched the dizzy since I've owned the truck.

The fuel might be an issue, but this rig got a new pump and filter in late 2009. Not meaning it isnt a possibility, but I'll check the ignition stuff before I do the fuel system.
 
I'd say change the fuel filter. Having just gone through a bout of tank/filter problems, it sounds familiar. the engine will run fine at idle but as soon as it's under load it would stall. Sounds like your problem.
 
It doesn't sound like a transmission problem to me. Probably spark or fuel related, as mentioned above.
 
Like they said. Fuel filter or wet dist. cap. Start with the Cap. look for moisture when you take it off.
 
cabledawg said:
More driving today revealed that when the engine is cold, it seems to run fine, but once it warms up, there's no power beyond idle. Unless I'm easy, and I mean real easy, on the gas, the engine will jump and sputter while driving. In neutral, I can rev the engine and its fine, but under load its rough.

I'll check the plugs/wires/dizzy/coil. Its a TBI so there isnt a vacuum advance, no worries there. The plugs havent been changed since 2005, wires since about 2006, the coil since 2008, and I've never touched the dizzy since I've owned the truck.

The fuel might be an issue, but this rig got a new pump and filter in late 2009. Not meaning it isnt a possibility, but I'll check the ignition stuff before I do the fuel system.
Click to expand...
Almost 3 years ago you changed the fuel filter, that is long enough it could be clogged again, I would definitely do that.
I am pretty sure it;s fuel related, nothing else, if the fuel filter doesn't solve it, the fuel pump would be the problem, it's not keeping up with the fuel, that is the problem.
At idle or even with no load it will require less fuel volume.
 
Anyone familiar with WinALDL? I have that loaded on my laptop and a cable to hook up to the ECM. Think any of the ignition stuff might show up on a diagnostic check? I'm not getting an engine code but that doesnt mean much.
 
Id be checking that fuel filter, they are only 4 mic filters with very little room for junk in them. I change them yearly on customer cars and it is surprising how many of them are very restricted.
 
The tank still has 20+ gallons of gas, so I'm avoiding the fuel system as much as possible (if it wasnt obvious). Might have to cut a hole in the floor. Been meaning to do that anyways..................
 
Duh, I was thinking about the sock filter in the tank. :doah:

Yeah frame filter is cheap and easy to replace. Might still have a spare in the garage, but we're fixin to move soon and I think it's packed already.
 
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