Cold start problem

jims47 · January 13, 2005

Truck '88 K3500 454 W/auto tran. 76,341 orig. miles

Recently since the cold weather hit I have been having a problem during a cold start situation. When the temp is above 45/50 it starts/idles fine. When it gets colder the problem gets progressively worse. If it is say 30 or so degrees out, the truck starts right up, but, it runs real rough, shaking backfiring through the exhaust. No fast idle. Now here is the part that gets me. After running like this for about 3-5 mins depending on how cold it will all of a sudden run perfect,ie: no shaking/backfiring and the fast idle is correct. The problem doesn't occur when the temp is above 55 atleast not noticable besides a few very small exhaust pops for about 1 min. After it warms up during this problem and quits the shaking etc. it runs normal, power is there with the exception of a slight dead spot at about 1/4 throttle-sometimes. I replaced the TPS,map sensor, temp sensor(on intake)[helped slightly] egr, cap ,rotor, plugs, wires, coil. I took the IAC out and the bore is clean. Last year rebuilt the TBI, put in a new distributor, and recently swapped the ign. module with no change. I swapped out the ECM no change. I am at a loss as to what the problem could be. I also went over the grounds and cleaned them up. I do have a cracked exhaust man. on the O2 side, not bad but it's a bit noisy till it warms up. The O2 sensor is two years old could this be a problem? The only code set is 44-lean-. and that sets randomly.

Any suggestions are very welcomed.

Jim

PS: no scan tool available

PPS: Air pump has been diconnected for four years, the problem started this year, so that item will have no bearing on this as it ran fine other than a bad distributor for 3+ yrs.

71GMC_3/4T · January 13, 2005

My guess would probably be the cracked exhaust manifold, especially since it's on the O2 sensor side. It could be sucking air due to scavenging and causing the O2 sensor to get strange readings.

If you knew what the O2 sensor should read resistance wise when it's running normal, I'd try putting just a plain resistor in place of it to engine block ground and see if you could fake it out to determine if it's the root of your problems.

About the only other thing that comes to mind is the distributor cap. Maybe it's got a crack or moisture in it. However, I think that would cause more backfiring through the carb and not the exhaust.

jims47 · January 14, 2005

My guess would probably be the cracked exhaust manifold, especially since it's on the O2 sensor side. It could be sucking air due to scavenging and causing the O2 sensor to get strange readings.

If you knew what the O2 sensor should read resistance wise when it's running normal, I'd try putting just a plain resistor in place of it to engine block ground and see if you could fake it out to determine if it's the root of your problems.

About the only other thing that comes to mind is the distributor cap. Maybe it's got a crack or moisture in it. However, I think that would cause more backfiring through the carb and not the exhaust.

<{POST_SNAPBACK}>

Thanks for the reply. I pretty much eliminated anything ignition wise. I thought about the O2 but since this problem only happens when it is cold out, IE: below 50 degrees or so and is worse the colder it is. But, I was under the impression(probably wrong) that the O2 doe not come into play until it itself warms up through exhaust heat. Since this only happens when it is cold, do you still feel it may be the O2 sensor? I can put it in gear and drive right off, it will miss a little but it will drive ok, with the idle being correct, until I throw it in neutral, at a stop sign or side of the road, then it does it's shaking poping etc. until the engine temp reaches about 150, then it's like nothing ever happened, really perplexing. Jim

BigRed8100 · January 14, 2005

I had the same problem a few years ago and my cap/rotor was the cause. Replaced them and its been running good for the past 2 years - even this morning at 16 below. The only issue is that you said the cap/rotor were already replaced.

71GMC_3/4T · January 14, 2005

Ahhhh... But just because it's new don't mean it's good!

I've had a couple of bad distributor caps, among the long list of other "brand new" junk parts.

gcarnrick · January 14, 2005

Ahhhh... But just because it's new don't mean it's good!
I've had a couple of bad distributor caps, among the long list of other "brand new" junk parts.

<{POST_SNAPBACK}>

I have an 1989 3500 with a 454 as well and I had the EXACT same problem as you described. I mean identical - backfiring/rough when cold and not when the truck was warm. The colder it got the worse it ran when I first started it.

I replaced the wires, plugs, cap, rotor, EGR valve, EGR solenoid, TPS, IAC, MAP sensor, 02 Sensor, distributor, ignition control module, TBI gasket, intake gasket - I mean every freaking sensor there possibly was.

We'll it ended up being that piece of garbage autozone distributor (which was the only thing I didn't buy from GM). It had a lifetime warranty so I swapped it and it now starts beautifull.

Good luck

-Greg

jims47 · January 15, 2005

Ahhhh... But just because it's new don't mean it's good!
I've had a couple of bad distributor caps, among the long list of other "brand new" junk parts.

<{POST_SNAPBACK}>

I have an 1989 3500 with a 454 as well and I had the EXACT same problem as you described. I mean identical - backfiring/rough when cold and not when the truck was warm. The colder it got the worse it ran when I first started it.

I replaced the wires, plugs, cap, rotor, EGR valve, EGR solenoid, TPS, IAC, MAP sensor, 02 Sensor, distributor, ignition control module, TBI gasket, intake gasket - I mean every freaking sensor there possibly was.

We'll it ended up being that piece of garbage autozone distributor (which was the only thing I didn't buy from GM). It had a lifetime warranty so I swapped it and it now starts beautifull.

Good luck

-Greg

<{POST_SNAPBACK}>

My thought was the distributor also. I replaced the stock one with a MSD unit last year. But knowing anything can fail, I borrowed a distrubutor from a friends truck, we swaped for a week. Same problem. He had no problem, so I eliminated that. It must be a weak wire or something of that sort that is causing this when it is cold only. Yesterday it was 68 degrees out. I went out started the truck and it idled at 1250 smooth as silk. Today the cold front went through and it was 34 out. I went out started it, shaking, popping through the exhaust until it warmed to about 150 and then like a switch turned out, it smoothed out continued the proper fast idle and idled itself down as required. Thinking just maybe the temp sensor(new one) might been a bad one, I went to the GM dealership put in a AC Delco and same problem. So far, new tps,new egr, new fuel filter, 1 yr. old MSD distrubutor, new cap, wires, plugs,module, coil(1 yr/old msd blaster) I tested the pick up coil it checks out. I am going to replace the O2 sensor even though this one is under a year old. Fuel pressure is ok, timing @6 degrees(tan wire disco'd) dist. advances fine. If the O2 doesn't change it I may just put on my Holley fuel pump and the 750 Holley and call it quits with FI and ECM's. I'm from the old school gearheads and do realize that FI etc. is definetly the way to go but not at this cost/aggrevation. If I wasn't disabled and on a fixed income now I probably would have that GM Tech scanner or the Snap On 2500 but for me that is out of the question now. I do have some old BB stuff from my younger days when this was fun. A BIG thanks to all for ALL of your thoughts/suggestions. It's probably something(as always) stupid, but right now I'm not stupid enough to figure it out

gcarnrick · January 15, 2005

I contemplated the same thing - giving up on the FI and going to a carb. I actually almost put in a distributor with mechanical advance as well.

The only thing that I could think of would be the intake manifold gasket as they are known to go bad. I would expect you would get a high idle though...but actually you did say there was a lean check engine code so maybe we are onto something. I replaced mine and it really only costs about $20.00 for the gaskets. Most of the work is in the 4 hours of labor it takes. Maybe with your experience it will be worth an afternoon just to eliminate the posibility

-Greg

Mighty HD · January 15, 2005

does it backfire loud enough to make gangsters duck?

jims47 · January 15, 2005

I contemplated the same thing - giving up on the FI and going to a carb. I actually almost put in a distributor with mechanical advance as well.

The only thing that I could think of would be the intake manifold gasket as they are known to go bad. I would expect you would get a high idle though...but actually you did say there was a lean check engine code so maybe we are onto something. I replaced mine and it really only costs about $20.00 for the gaskets. Most of the work is in the 4 hours of labor it takes. Maybe with your experience it will be worth an afternoon just to eliminate the posibility

-Greg

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I put new gaskets on it last summer when I rebuilt the TBI. I figured since it was off I was half way there. I have good Vacuum with no ups/downs. It's something to do with the weather temps. I just have to figure out what. I think I'll tear the wiring harness apart where the temp sensor wire enters and see if something is amiss there.

dcalex · January 17, 2005

One trick (at least on the old carbuerated engines) to diagnose an intake man. gasket would be to take an unlit propane torch....turn the gas on and flow it around the manifold gasket area....see if the engine runs up.