Won't idle...

[KRB64]

OK, help me think through this. The M880 is the farm truck. Mostly short drives on the road, off road too. Goes to town every now & then.

The other day I added a 5 gallon jug of gas (filled this summer) to the tank then headed down the road. I noticed it had a flat spot but I assumed it was because this truck is VERY cold natured and she wasn't warmed up yet. But after heading back home it got to where it wouldn't idle. Otherwise ran out fine.

I checked the fairly new vacuum lines, plug wire connections, coil connections, carb nuts & screws and carb linkage (Carter BBD I over-hauled a few months ago which equals several hundred miles). In the interim I saw lots of bloom on the battery connections so I took them apart and cleaned and greased everything back up.

I figured I got a bad batch of gas or it had absorbed water while sitting for a month or three. So a I poured a thing of dry-gas in and few days later pulled the fuel line and inserted into a jug of good gas. Idled fine so I figured that was that. I plumbed it back and for kicks I started her up again and she ran fine. So I figure not the fuel but something must of been lose that I didn't notice? Maybe the battery connections were so poor that it didn't have enough juice to idle off the alternator?

Drove a few miles on road and ran great. Then, today went into the woods to load up a load of firewood and it started all over again. Dang near never made it out as the hill was steep, the ground was thawing and the old truck wouldn't idle which is what I needed to get out. Above idle it runs OK.

I've played with the idle mixture screws to no avail - will run with them in or out and in between but won't idle either way. Is this a clue?

Am I overlooking something obvious? Could this be electrical even though I'm thinking fuel? The distributer and coil are fairly new as are the plugs and wires. Not sure how old the ECU unit is but its not ancient. Not pulled the carb yet to clean that out although I did pull the top plate off to verify that the accelerator pump and jets adjustment hadn't slipped.

Thanks for any ideas or ruminations...

[oldmopar]

A bad EGR valve will cause it to not idle or idle poorly, if it has one

[Don Williams]

Had similar situation on my M886 and tried several different things. In my case a carb rebuild was necessary as the bad gas had really done a number on it.

[KRB64]

I'll clean out the EGR valve. Its all gunked up and oily on the outside.

Took the top off the carb and looks clean inside but of course I can't see all the orifices. I'm thinking it wasn't bad gas since it ran fine for a while afterwards. Maybe the EGR valve is intermittently sticking. That's one thing I've neglected to ever change or clean out.

[KRB64]

Cleaned the valve, it was dirty. And I "think" it seems to have helped some but still not idling correctly...

[Gordon Maney]

Secure an air hose nozzle with a conical, rubber tip. Remove both idle mixture screws, place the tip against the empty holes, and apply a good blast of air.

Begin your idle mixture adjustment with the screws at 2 turns out from [carefully] bottomed.

[KRB64]

Thanks Gordon, I'll give that a try. Never knew if that was OK to blow them out that way.

I guess (know) my carb is worn out as well. It has always, since I've owned the truck, been around 4-5 turns to idle right. I've rebuilt it 3-4 times since rescuing the truck from the scrap yard.

[Gordon Maney]

It works sometimes.

[KRB64]

Well that did "seem" to help or maybe it was just wishful thinking? I guess I'll pull the carb and clean it out and readjust unless somebody can think of an electrical rabbit for me to chase...

[Gordon Maney]

Disassembly and thorough cleaning is always a god thing.

[712edf]

FYI today's pump gas is reputed to have a short shelf life. I know lawn mowers & small engines regularly need their tanks drained & cleaned out, more so today than before we were blessed with ethanol. I suspect the same could be said of full size vehicles.

I have seen suspect gas cause poor idle but still have decent cruising/driving.

Bucky

[KRB64]

Yea, I really hate ethanol, especially in overwintering our boats.

It was about 5 gallons I added and there's about a half a tank in there, maybe I'll just fill it up & dilute it.

[n1265]

I have never seen an M880 with an EGR valve. They usually have a metal plate over the hole where it would bolt ( on a civilian truck ) to the intake manifold.

That being said, I have heard that if the gasket for this plate is gone or if the intake manifold is rusted under that plate it will cause idling issues.

However, I do not know if this is true.

If your truck does have an EGR valve, I wonder if the same could be said about the idling issues if the intake is rusted ( passage ways compromised)
under the EGR ?

I would like to know for sure, because I am also having idleing issues with my M880 , but only after it idles for longer periods of time.

[KRB64]

Sorry, PCV valve.

But you bring up a good point. I'll pull that plate and maybe replace the gasket, good to know.

Well maybe not tonight, windchill -1. I know that's wussy weather for some but that's dang cold here below the Mason-Dixon line...

[KRB64]

Finally got around to tearing down the carb.

Float bowl was full of gel that looked like rubber cement. I assume this is ethanol separation.

I cleaned everything, put it back together and she ran fine. I guess I'll need to drop my tank and clean it out though. No telling how much of that crap is laying down in there...