My 2002 2500. Something seems to have quit the other day. It was fine until I came out from a store. Started hard and ran rough, then at the next store I shut it off it would not start until it sat for an hour. Idled up and fluctuated a lot. Once going it got me home okay but the idle level was higher than normal the entire drive.

It has always started hard, it needs to crank a few seconds, stop and crank again about 90% of the time, once in a while it kicks right off.

My code reader showed a soft P0101 for the MAF out of range, so as an experiment I just unplugged the lead to it and I got it to start and run. So I swapped out the entire air filter box from my 3500 to see if that solved the problem. It then started normal, so I presumed maybe that was it. But I didn't drive it anywhere.

Last night I drove it about 3 miles and it did the same thing. Would not re-start when I shut it off. I let it sit running before I shut it off and it idled up a bit, randomly. An hour later it started but just barely ran the first few seconds, acted like it would stall. Giving it some gas it hesitated then picked up and ran normally. Once it gets past that it drives okay. The longer it sits the easier it starts, if it's stone cold then it starts best, but will still hesitate a touch when going into gear.

I tend to not suspect the fuel pump because once it runs it goes and it drives fine. I know the pump can get weak but typically they work or they don't. I do have a cheap HF pressure tester here but I'm somewhat afraid to use it since the reviews for it say you have about a 50-50 shot it will leak fuel everywhere. The code reader I have will check the O2 sensors and if I read that right it said they were reading on the rich side.


So right now tentatively the plan is to go out to the you pull yard, find one marked that it ran and drove and pick a cap, rotor, crank sensor, another MAF, and some other stuff off it and swap parts around and see if any of that solves the problem. Then once I know what it is I can order up new if I want and change it again.


It did this one other time, would not start, back in the winter after stopping to eat on my way home. Let it sit then about 10 minutes and it started. The only thing connecting these two events is I had the AC on that night trying to defog the windshield. And this last Sunday, it was hot so I had the air on. It seemed like in both instances it acted up I had shut it off with the AC control set to on. The AC pump is a strange shade of green under there, but it does work and blow relatively cold air.

 

Just wrap it in a rag. What's the worst that can happen?

 

a fire, I suppose.

All the symptoms indicate it's getting fuel and not burning it. When it refused to start that first time I sprayed a couple blasts of start fluid into it and got nothing, not even a pop. That tells me no spark. Hesitation and not running well tells me probably a weak spark. Then whatever it is clears itself out and it runs more or less normal, except for the changes in idle speed.

 

I read through a long thread on Edmunds and came up with a long list of possible things -

MAF bad
Cap & Rotor worn, damaged
Coil bad, leaking spark or not working
Distributor body cracked or worn inside
Coolant temp sensor bad
Ground by CTS damaged
Crank Position Sensor bad
Computer case damaged, allowing water inside (seems unlikely since it was a hot dry day)
Ground at computer corroded

Going to throw one more on there, if the coolant is low perhaps the sensor is reading steam and thinks it's overheating, I presume GM still uses separate sensors for the computer and for the dash cluster on these since the interchange on the CTS on the top of the engine swaps to about 10,000 other cars. My old Suburban the coolant got low in and eventually the gauge started reading wonky because it would get either no coolant or steam or something in there.

 

I don't think the coolant temperature can prevent the engine from starting.

 

All I can tell you is one guy reported his would start, run until it got hot, then die and no start, the cure was changing the ECT sensor and by the sound of it they cleaned up the ground next to it.


As for mine, I just went out and was able to get some live data out of it.

Oxygen sensors around .9 volts, B2S2 at .8, STFT for bank one both at -10.9%, for bank 2 at 99.2%

Idle 1050 RPM, but it would click a relay and speed up for a bit then slow down, about four times before it got to operating temp

Spark advance varying from 20-20.5-21 at idle

MAF at 123
IAT 120' F
MAP at 9" in/hg

Now the one that concerns me is the ECT showing -36' F. It's about 83' F outside.

So I'm going to buy an ECT and see what that does for me since they're a whopping $20 or so. And clean up the ground while I'm at it.

And once I shut it off, it would not restart, as before. Maybe the computer thinking it's so cold is flooding it out with excess fuel.

 

This acts like a loose electrical connection, somewhere. I'd recommend revisit all you have done on the electrical side.

 

I haven't done anything to it whatsoever except swap the airbox out for a second one to change the MAF.

There is a second ground on the back of the engine I may examine.

I went back out after it sat a bit and checked again. ECT at -38'F, turned key, cranked, started, then almost immediately died.

 

And ultimately that ECT was the problem. It was so bad the plastic end for the connector snapped off as I was removing it, partly because there's an AC line that prevents a straight shot on it with the socket. I changed it and went back to the live data and it showed 83' F. I started it, it stalled, started it again and let it idle and it idled down low and smooth and ran fine. I could goose the pedal with no hesitation. Once it got to around 170' I shut it off and was able to immediately start it again. I wouldn't be shocked if it's been bad as long as I've had the van (the fuel economy has never been what it should be), I just never had a way to see live data before to see the problem.

I noticed about 5 degrees less timing advance and the O2 sensors showing lower voltage which I presume means less rich. I would guess that the computer thinking it was like 200 degrees colder than actual temp (when engine hot) had the timing and mixture so messed up it was washing the spark out, or the timing so far off it wasn't enough to burn the mixture. Either way, it wouldn't start. It just happened to finally fully fail a week ago Sunday.

Thinking I should change the oil next, I wouldn't be shocked to find it has some gas in it.

So the good news is for all the problems this could be it was a 5 minute $20 repair I didn't even have to get very dirty for. Although I had to spend like $130 on a scan tool to show me the problem.

 

common cause for a hard start after a hot soak is fuel pressure leakdown. install a fp gauge and prime the system. watch for a pressure drop. if you have a diaphram fpr...pull the vac line off and check for the presence of fuel.