Question for Diesel gurus

[67charger383]

Haven’t started my truck in about a week.
It was 50* out so I didn’t use the block heater.

(it’s a ‘87 F350 dually. 6.9 idi/t19 4 speed)

Started right up after a few cranks, then I had it idling for 5ish minutes. I do this a lot with this truck because it doesn’t have tags yet.
Had it warmed up and went into low idle like it should.

Anyway, it randomly started revving up without me touching the pedal, and I immediately killed it with the ignition. Only did this for about 1-2 seconds before I cut it off.

Looked over everything, no leaks, didn’t blow up, nothing got sucked in the intake.

waited about 5 minutes and went to start it again, seemed like it was cranking faster than normal so I stopped.

What the hell happened and how do I fix it?
It’s a low mileage truck, but I suspect it might be injection pump failure or lift pump failure?

 

[R413]

I own one also. Unsure of what it is. Happens to mine after I let it sit for a month. When I start it and idle it, does about a 200 RPM change in idle speed. Doesn’t seem to hurt anything and if I drive off it goes away quickly or won’t do it at all. Been this way for years. Truck runs good and fuel mileage hasn’t changed.

Yes it will crank faster after running for 5 minutes, the oil is warmer and the batteries have more voltage.

Has the injection pump ever been rebuilt? I did mine at 80K and the guy said the aftermarket rebuilt parts updates them and will last longer than the factory pump.

 

[67charger383]

I own one also. Unsure of what it is. Happens to mine after I let it sit, then start it and idle it. About 200 RPM change. Doesn’t seem to hurt anything and if you drive off it goes away quickly or won’t do it at all. Been this way for years. Truck runs good and fuel mileage hasn’t changed.

Yes it will crank faster after running for 5 minutes, the oil is warmer and th batteries have more voltage.

I’m new to the whole diesel thing, first truck.

 

[bearman]

In some ecm's they have a cold start feature and after fire up the idle will be higher for a minute or two depending on engine temp. As for cranking easier after it ran see the above post. As for it jumping around on rpm once do to temp it will settle down once you reach engine temp

 

[ESOXER]

It'll do that till they warm up, Cummins has a grid heater if it's not working properly or removed it'll do the same thing. I had mine return to high idle before, just be easy on it till warmed up.

 

[69bird]

Both my cummins jump in rpm when it is trying to heat up the block I let mine warm up for 30 mins or so it only jumps 200 or 300 ram for little bit I know if you push on brake when it goes in high idle it will kick back down on a auto truck but on my 6 speed it won't till your engaged in a gear and let out on clutch

 

[ESOXER]

I was always told only 5-10 minutes to warm up, any more and you'll get cylinder wash and diesel in your oil. Not sure if it's true or not.

 

[R413]

I’m new to the whole diesel thing, first truck.

I should ad that I worked at Ford dealers and was factory trained on these Diesel trucks. A Cummins is a way different animal.

A 6.9 Ford doesn’t have an ECM. The only thing close is a intermittent wiper controller and the ABS module. LOL

The fast idle is controlled by a temp sensor that drives and electric solenoid to raise RPM. It goes open at 140 degrees and the idle comes down. This solenoid is not strong enough to move the throttle by itself, you have to push the accel pedal down then the solenoid holds the throttle at higher RPM.

The reason for this long explanation is that the solenoid is not causing the idle fluctuation as it cannot open the throttle, it just holds it higher.

 

[69bird]

I was always told only 5-10 minutes to warm up, any more and you'll get cylinder wash and diesel in your oil. Not sure if it's true or not.

Just think if the 5 to 10 min warm up time would hurt anything all the big trucks wouldn't let there trucks idle for hours

 

[70bigblockdodge]

Always idle rpm up a diesel if extended idle time. I don't know if the electronic engines have a idle bump or a idle up off the cruise control like a big truck. They did sell throttle sticks years ago to push and hold the pedal down making it idle high.

 

[ruffcut]

Yes, a Cummins will idle up 200 rpm if started in cold and left to idle for a few minutes. Nothing new. ruffcut

 

[yella71]

Your problem is the little blue oval in the grill. seriously there is nothing wrong with it other than its a 6.9 IDI.

 

[R413]

6.9 is a bullet proof engine with no problems. You just need to plan some extra time to get there. You can’t go 80 UP the mountain pass with your 35’ travel trailer like the cummins Millenials do.

 

[Cojohnso1]

My Cummins will do this a couple times. Mine appears to be alternator kicking up due to dual Batts a little low? Always has done it after extended time down.

 

[64BEL]

I know, off topic a bit, but since we've gotten into it.... The Cummins will idle up when the temps are cold enough, as has been stated. When the outside temperature is really cold, it'll shut down 3 cylinders and run on just 3 to warm up faster. Sounds like it's going to break apart - pretty entertaining. I added a BD Diesel high idle to mine. When I want to warm it up, I can just crank up the idle in the driveway and let it rip for as long as I want without washing down the cylinder walls. It really won't ever warm up if just idling normally.