3500 mile update on hot-rod 6.2L

[arveetek]

I've put about 3500 miles on the new 6.2L since rebuild. She's running great! No repairs have been needed, except for a sheared a/c compressor belt...not sure what happened there..the belt just seemed to separate.

The engine starts great every time, with just a hint of a puff of smoke on cold startup. Drives like a dream, and pulls strong and hard. The first 120K miles I had this engine, it used a quart of oil every 1500 miles. Now it's only using a quart of oil in 3000 miles. I'll have to wait and see if that's consistent.

The only problem I haven't resolved is the bad idle. When started cold, it idles and sounds great. After it warms up, the idle gets rough and sounds like the timing's off. I've adjusted the timing, jumped the HPCA when warm, and it doesn't matter. However, another strange symptom is after pulling really hard with the RV in tow, I can pull into the driveway, and the idle is absolutely perfect, just like I think it should sound. But after a couple of minutes and a little cool down, it goes back to the rough idle. So when it's cold, or really hot, it idles great, but in between, it sounds like a worn out engine.

It has to be in either one or more of the injectors, or the injection pump. I'm not sure which. I haven't had time to swap either out, but I will one of these days. Everything on the engine is brand-new, so it shouldn't be either, but that's all I can come up with.

I haven't checked fuel mileage yet, been too busy keeping my foot to the floor and watching the boost and speedometer needles climb! :D But I just filled up Friday, so I'm going to try and take it easy on this tank full, and see what I get, empty. I'm guessing 17-18 mpg. Towing, I avereaged 11 mpg.

Casey

[wthif]

Your idle sounds familiar to me. My engine was also doing something similar; it reminded me of a engine with a rough idle cam (not sure if that is what they are called). I chose to ignore it mainly because I could raise my rpm by about 100 and if not less and it would go away. From what I can tell any more is the idle is fine. The problem, if that worked its self out. So maybe time will tell.

By the way I kiss 20 mpg every once and a while. Difficult to do when you are driving 80 mph even then it is no lower than 18 mpg. I never really tow anymore so can't help you there but I do live in the mountains. I think that I only get 12-15 mpg in the mountains. Also what kind of EGTs are you getting towing (how heavy?) and empty. And how does your coolant temp do? I run around 195 but it not uncommon on a grade to hit 215-220. Usually cresting the hill once temps reach 220 so never felt a need to back out.

The reason I ask about your temps. Is I will towing a Model A on a trailer from Portland Maine to California next summer or the summer after that and I currently not sure if I could tow and keep EGTs and coolant in line.

Glad to hear all is going fairly well and that your are enjoying the engine. I'm still enjoying mine almost two years later. :D

[spitfirenut]

I'll say it runs like a dream! Went up to see Casey about a month ago and was duly impressed by the pavement shredding 6.2. That's one healthy engine! :D Hopefully, your idle question will be answered one of these days. It sounds different for sure. Not necessarily bad, just different. Anyway, enjoyed the visit. It's nice to attach a face to a name.
Don

[john8662]

Glad to hear it's still together! tongue.gif

Talking about more power makes me itch! I've got the 6.5 sitting on the engine stand (Saturday's project) and the 6.2 on the other (they look so cute). I need something with a little more power than what I'm driving now...

The Idle problem, your idle problem does sound like the "worn engine" symptoms, my truck idled really poorly, when worked hard it was decent for a little while like you describe. Also seemed that the longer the engine ran, the worse it got..

Things to ponder about the idle though.

1. It's probably not the pump, since it's reman and fresh.

2. It could be the injectors, since you had one that had a loose body. I'd want to take them down to a diesel shop and have them tested to see how close they are to one another (pop pressure).

3. Lifter, didn't you say you had a tickin' lifter? Check here, or has the tick completly disappeared?

4. Valve train in general, when you had the heads rebuilt, did they check the spring pressure, among other things? My local shop rebuilt my heads, and when I asked about spring pressure, they said they never check. I have them taking them back apart to check this out, and replace and or shim those that are in need.

[arveetek]

wthif,

My egt's never go over 1050* at full-throttle, unless I lug the engine and let the boost fall. Less boost = higher egt's. My main problem is engine coolant temps. Pulling hard up a hill makes the temps climb fast. I've found unlocking the spring on the fan clutch and keeping the fan pulling air at full blast at all times keeps the temps reasonable. So for the moment, when I hook up the trailer, I unclip the fan spring. Upgrading the cooling system is next on the list.

Raising the idle 100 rpm doesn't make my problem go away or go unnoticed. I have to get it above 1000 rpm before I don't notice it anymore.

Don,

Same here...it's always great to put a face to the user name! I had a great time, sorry I couldn't have spent more time with you...it was a busy weekend. I assume you're safe and sound back in NC after the Oklahoma training?

Casey

[arveetek]

Thanks for the ideas, John!

No, I'm sure the shop didn't check the valve spring pressures. Not a normal check, as you found out. I'm really quite sure it's not a valve train issue, since it appears to be temperature related. Cold = good, extremely hot = good, warm = not so good.

I do have a very slight lifter tick at cold startup, but it quickly goes away. I've pretty much ruled out a lifter problem from the symptoms I'm having.

Both the injectors and injection pump are freshly reman'ed, so that should rule them out, but you know how it is, and you're right, one of the injectors did leak at initial startup.

It's a weird problem that doesn't affect the running of the engine any, but it sure does annoy the heck out of me. Instead of being proud of my genuine GM diesel, I'm embarrased to let it idle for very long.

I'll get it figured out one of these days...I have a spare IP and set of injectors to swap around...although I'm sure the injectors are in pretty bad shape. But maybe they'll let me pinpoint the problem.

I'd better finish the wife's porch before I turn another wrench on my truck, though! :D

Casey

[Peter J. Bierman]

The TTD engine has the same ilde issue as discribed.
Fine when cold, a bit sloppy when warm.
Changing fuel filters seems to make it a bit better for a wile but putting an additional electrical lift pump inline does not make a differance. :(
100 to 150 RPM extra makes it go away but I like it to idle at 550 RPM in drive ( 650 in Neutral ).
All this started after the build up and did not change with the new Marine pump or the new high flow/pop injectors. :confused:

Actualy, I dont have a clue where to look next.
:mad:
If you find a solution, please let me know,

Peter

[TRASHCAN]

I have the same idle issues with my truck. I have checked and tried numerous things including new motor mounts. Just a little more peddle smooths it out quite a bit. I have learned to live with it, but sure would like to know what causes it.

[jcomp]

Just a shot in the dark, but maybe it's being starved for air at normal idle? Cold air is more dense so it's less of a problem there. Maybe a very hot engine produces hotter exhaust that has more volume and spins the turbo enough to feed the engine or at least not be a restriction.

Probably way off base but it might be something to check out.

[Vaughn MacKenzie]

My $600 '82 Banks-equipped Blazer has the same idle miss as described here. So does my buddy's '84 Blazer. But my other Blazer, the crapola one out in the pasture, idles smooth as pie at any temperature.

Vaughn

[5.7L oldsdiesel]

On some of those DB2 injection pumps that have the steel governor cage,these sometimes create excessive play in either direction when rotated by hand.The steel governor cage is now standard on all DB2 pump rebuilds as many know,but they do create the rough idle when they allow excess play.I came across two 6.2 diesels that did this.I replaced the governor cage in both pumps,and the rough idle has never returned on either engine.Not saying of course this is your problem,but certainly a possibility.

[arveetek]

Thanks for all your thoughts, everyone.

What's really odd is that my engine idled just fine before the rebuild. It had a massive lifter knock, but it idled smooth as silk, even with one broken compression ring! Now that I totally rebuilt the engine, along with new injectors and pump and timing gears, it idles terribly! :confused: It does run a heck of a lot better, but I can't stand the idle!

Casey

[john8662]

5.7L oldsdiesel,

Would you care to elaborate a little more on the cage of the DB-2 pump?

Whats the acceptable slack, whats excessive?

Pictures would be nice of exactly what you're talking about, and what it's going to take to diagnose.

[5.7L oldsdiesel]

Sure.I'll try and get some pictures together and hopefully everyone will know what i'm talking about.It's a pretty simple thing once you see the pictures.It's amazing how something like this can cause so much grief with a rough idle.

[arveetek]

Just wanted to update ya'll on my fuel mileage.

I haven't really checked the mileage when running empty until just this past week. I kept an eye on the fuel guage and tried to keep a light right foot, but normal driving with mixed city and highway miles yielded a dismal 15.6 mpg. I'm pretty disappointed. This truck used to produce 18 to 19 mpg pretty easily. But now that I've tweaked it and made it to pull like a son of gun, the fuel economy is suffering. No surprise, really, considering I've increased the fuel flow with a 4911 pump and turbo injectors. Still, I was hoping for more.

Perhaps the fuel mileage will get better with more miles on the engine. I'll have to keep an eye on it. What's funny is that the fuel mileage increased while towing. My RV trip to Ft. Worth produced an average of 11 mpg. It used to use more fuel at a slower speed. I guess it was struggling so hard, it had to burn more fuel. Too bad that doesn't translate into higher solo mpg.

Casey