Hello all,

I'm new to this forum, just signed up. I'm at a loss with my truck. In June, I was towing a light pair of jetskis up a mountain pass and it started to run very rough and has been doing it since.

Here's the bad news: it's a 4.3 liter 6 - but has run fine until now.

I've replaced:
ECM, plugs, wires, cap, rotor, coil, O2 sensor (only one, upstream of the cat). Plugs didn't look fouled but they weren't in great condition either. I also replaced the knock sensor and the fuel pump/filter (which helped, but didn't fix - do the TBI injectors go bad on these?). I've set the ignition timingjust for good measure. You have to unplug the timing advance wire to do this properly and I've done it a few times. I've checked trouble codes and am not receiving any.It runs horribly at idle, better under throttle but not great. I'm not getting a good pop sound when I rap the throttle, just a real flat sound, and as it calms back down to idle it shakes and shimmys as if it could die at any moment. It runs better cold. The roughness never goes away. I get a metallic banging sound at idle out of the cat which should probably be replaced, but I can't imagine that's what's making it run so bad.

All I can think of now is a compression test to see if I've got a bad valve, but I'm not getting any smoke, just a slightly richer smell from the exhaust. Other than that, valve timing I suppose. I'm just wondering if anyone has run into this problem and to see if you can offer advice. I heard that there may be a defect in the distributor shaft? Am I missing something?

 

could be a blown cat, but i wouldnt imagine making that much affect. have you replaced the pick up coil or the ignition module inside the distributor?

 

It could be the cat but I think usually when the cat is bad it idles just fine but bogs when you get on the throttle. Could be the coil or ignition module like stopspazinout said.

Have you checked to make sure all the sensors are plugged in and working? MAF and O2 sensor might cause that problem.

 

A blown CAT can make that much of difference actually. Another thing we've had to do with my truck. Which is, BTW, a 4.3 liter V6.I just had mine [CAT]taken off. Here in Oklahoma we don't have emissions testing so it doesn't really matter if it's there or not. You might want to check on replacing your MAP sensor as well.

 

I couldn't handle it anymore so I took it in for a diag. Zero compression on #1 cylinder, outstanding.

I'm at 158K miles, can't really justify having the heads done just to get a few more out of a tired engine. SO - I'm looking at a 5.7 swap. Look for me in another section.

Thanks to everyone for the advice, I sincerely appreciate it.