97 Suburban runs rough when warm

[scarp333]

I have a 97 1500 Suburban 4wd 5.7L 171,000mi that runs well when cold, but will barely run after 15-20 min of driving. It seems to act up when stopping after going up or down a hill. I have limped home a couple of times running rough at 10mph. It has thrown a P0341- Camshaft position sensor circuit range/performance and sometimes a P0339 -Crankshaft Position Sensor "A" Circuit Intermittent. It will start right up after it cools down. The fuel pressure is 64 at start up, 60-62 under load, and 55-56 at idle and no fast leak down. I have replaced camshaft position sensor and spark plugs. Compressions were all near 160psi. I don't know where to look next. Any help would be appreciated.

[scarp333]

Update: I got a hold my friends scanner. Cam retard was -7 degrees. I adjusted it to 0. Hope this fixes the problem.

[Scrapper]

that should work now and if it don't i'd replace cps first and check out your catlic coverter...

[scarp333]

It did not work. Truck ran well for a while then stalled as I was slowing down from 45mph and turning right. It took 5 min to start, then ran really bad. I could not get it over 1500rpm. P0339 came up again but no P0341. I'll look into the crank position sensor. I still don't understand what is going wrong. It seems very repeatable. It will stall/stumble when stopping/slowing when going up or down a hill.

[scarp333]

I put in a new crankshaft position sensor today. I tried to fire it up but it wouldn't start. I put the old one back in and it started right up. I also took a good look at the wires for the crankshaft position sensor. I did a continuity check on it from the connector to the PCM. I wiggled the wires, no breaks in continuity.

[chuck's]

Just a thought,but I have read threads that talk about worn distributor drive gears.This would affect cam shaft to crankshaft coordination.
chuck's

[scarp333]

I pulled the distributor and the gear was worn. Went to NAPA up the street and got the part and installed it. The whole process took about 1.5hrs. Started right up like always. I tweaked the cam retard offset from -3 back to 0. I was hoping this was the fix, but no, it started to stumble going down a bumpy dirt road. I limped home again. Got a P0341 this time.

It ran better(smoother) and for longer before acting up again, so I think the gear helped.

I am going to have the crankshaft variation relearn done next. I have messed with the harmonic balancer and crankshaft position sensor (replaced leaking front cover). Who knows what the guy I bought it from did to it. I should have been more wary when he said he was in sales, but the wife had to have a Suburban to haul the kids around in. She has to walk by her Suburban to put three kids into the Camry.

Anybody got any other ideas?

[chuck's]

You mentioned about your suburban started to act up when driving on a rough road.I have heard or read that cam shaft to crankshaft sensor correlation is affected on the rough road.With the distributor gear slightly improving the prefomance,I am wondering if the timing chain is worn?Does the timing stay steady when connected to a scanner?If it doesn't,that is a sign that the chain is worn.
chuck's

[scarp333]

Had the crankshaft relearn performed today. On the way home the truck acted up again. I replaced the timing chain when I replaced the front cover.

[scarp333]

I took the intake off yesterday and it was full of carbon. It was dry towards the front of the engine and moist with oil near the rear. the heads had some sludge in the valley tray and some carbon build up about an inch and a half into the intake runner. I'm going to clean the upper and lower intake and the injectors and put it back together with a new pressure regulator and see what happens. Anybody have any ideas why there would be so much carbon?

[J-Ri]

Probably 171k miles worth of EGR and PCV, depends on how much carbon there actually is in there, but I'd say it's normal unless you're chipping big chunks off. If you haven't already, replace the PCV valve, that should reduce the oil going in. For maintenance in the future, BG makes an induction flush that cleans the intake out really good.

[scarp333]

I replaced the Crank Position Sensor and it solved the problem. I must have got a bad one when I did it before. Now on to the A/C. Thanks to everyone who helped.