Surging at Mid to Full Throttle

[Mark K.]

Hello everyone,

I just picked up a 86 K-5 4WD Blazer with a 6.2 diesel. This is my third 6.2 diesel vehicle over the years and will not be my last, I really love these machines. The body is in good shape on this one (got it down south, no rust at all) but it's showing a little bit of use on the drive train at 140,000 miles. I've put about 2000 miles on it so far since I picked it up and just yesterday it started a surging problem going up slight hills and also out on the highway from mid throttle on up. The unit keeps running but it surges every few seconds as long as I am climbing the hill or am at speed on the highway. It clears as soon as I slow down or the road levels out. The first thing I did tonight was to change the main fuel filter up on the firewall but that had no effect. It seems like I've seen some notes on surging here before but there is so much material here I always have a hard time keeping it all straight. Anyway if anyone has any ideas on this please let me know. Is it possible a bad tank of fuel could cause this? Am not showing any water in the fuel but this did start with my most recent tank of fuel (perhaps just a coinicdence). Any thoughts would be appreciated and thanks as always for the great site. Thanks,

Mark

[britannic]

If it's surging under load, it might because of one or a combination of the following (list not inclusive):

1. Worn IP
2. Weak lift pump (see recent posts on checking it)
3. Restricted return line
4. Governor assembly malfunctioning
5. Air is leaking into the fuel system on the vacuum side of the lift pump and causing timing fluctuations
6. Leaking/worn injectors
7. CDR valve malfunction
8. IP advance mechanism malfunction
9. Other suggestions...

[Mark K.]

Wow what a list. I think I'll start with the lift pump. The problem came on almost instantaneously and then seems to have stabilized at its current level. It seems almost like a clog in the fuel system or perhaps an air leak like you suggested. Hopefully not the IP but it does have close to 140K and you can tell it's been run pretty hard, lots of towing. I'll start to work it through though. Thanks for the help and it's great to see an M1028 there in your listing. I have a 1988 4.10 geared version of this (dually 4wd, 6.2) which was a government purchase used as a snow plow truck in Wash DC. It's almost a M1028 CUCV but not quite, it was ordered with all the heavy duty 4wd options though as near as I can tell. It's rare to see the dually version and I hope one day to pick one up an actual M1028 for a restoration project (time permitting). Thanks again for the help, it's appreciated,

Mark

[dieselcrawler]

Hey... I am having simular problems with my truck...('84 CUCV 1028 military K-30) I think my question is this: How can you tell if it's the IP going bad? My truck has been surging as you drive down the road at a steady speed, and sometimes stalling at idle. Untill now, it has always started back up, but had to crank it a while. I have replaced the fuel pump, just tonight, as well as checked all my fuel lines. Didn't get a chance to try to start it with the new fuel pump, it was late and I didn't want to wake up the grumpy old lady next door with my noisy truck! I hope this cures the problem, but I fear the worst, that the injector pump might be on it's way out... any help/info/insight will be helpful, I'm new to the diesel thing, only had my truck about 9 months, and not sure how to troubleshoot things yet. Thanks, DieselCrawler

[britannic]

The best way to check the IP is to remove it and take to a shop that can test the calibration, pressures and timing. Otherwise, mileage is a good guide, once the IP is over 100K, prevention is better than cure.

[gmctd]

Adding to Brittanic's list - restricted supply line, from sock in tank, thru dual tank valve, up to mech lift pump at engine.
Dis-connect lines and back-flush with shop air, noting that if you back-flush into tank, it will happen again, soon.

[dieselbegreat]

Ya know, sometimes it pays to have an extra known good pump lying around. It was worth my time to buy a pump from www.mwfi.com (http://www.mwfi.com) for about $250 (reman to pump# of your choice and it was like brand new!! and ran great) I bought a similar pump on eBay for $25 just for core return. I still have the one I took off which was running pretty good!

[dieselcrawler]

I got my truck running again... took a while to get the lines bled, and it had to crank a bit before it would fire up, but it did. Found a fuel leak coming from the bottom of the fuel filter. Guess I need to find that, then I'll actuly MOVE it, and road test it. However, just revving it in the driveway, it still seems to have a hesatation, like it's starved for fuel. What are the symtems of an injector pump that is on it's way out? What about other things? My truck has just over 100K on it, so it may be that it's time for a new/rebuilt IP... So if I do that, I'll need to re-set the timing, right? Can I do this my self, or must I go to the local dealer? What about installing a used IP? (it's free, from my uncle) Is it worth the time and effort? If I plan on installing a turbo at some point, is there another, better pump to use? Would I then need to change the injectors? I'm new to this, and starved for knowlage, so I'll ask alot of questions... **grin** Thanks again, DieselCrawler

[britannic]

Air leaks can definitely cause hesitation and stumbling, so they will need fixing before any further diagnosis can be made. If the filter is on the pressure side of the lift pump, then it'll only draw air when the engine is shutdown.

Before installing an unknown inj. pump, it would be good to get it checked over at a Stanadyne shop.

[CleviteKid]

. . . and sometimes all you need is a good "Freeway Tuneup."

My SAA engine doesn't get to perform at full potential very often, and lately had been letting me know by bucking just a little bit at the lower end of 4th gear locked up on the 700R4. This past weekend it was finally cool enough in Miami to do some good 0-60 runs with the new transmission from Fourth Gear Inc. outside Orlando. The results will be in my upcoming article on 700R4 trannies, but let's just say the times are better than the last report. :D

Since the exercise, my SAA is much happier around town and runs with its original smoothness. So I will be visiting the "2 Fast 2 Furious" strip of road in a secret Miami location every couple of months to keep my engine happy.

Dr. Lee :cool:

[britannic]

Originally posted by CleviteKid:
. . . and sometimes all you need is a good "Freeway Tuneup."

My SAA engine doesn't get to perform at full potential very often, and lately had been letting me know by bucking just a little bit at the lower end of 4th gear locked up on the 700R4. This past weekend it was finally cool enough in Miami to do some good 0-60 runs with the new transmission from Fourth Gear Inc. outside Orlando. The results will be in my upcoming article on 700R4 trannies, but let's just say the times are better than the last report. :D

Since the exercise, my SAA is much happier around town and runs with its original smoothness. So I will be visiting the "2 Fast 2 Furious" strip of road in a secret Miami location every couple of months to keep my engine happy.

Dr. Lee :cool: :D Another compelling reason to move nearer the mountains and turbo that bad boy truck of yours!! :D :D

[Dieselboy]

Everybody's doing it. Do you feel the peer pressure yet, Doc? :D

[CleviteKid]

But if I put a turbo on it, what would I do with my "Swanger Air" air cleaner ? ? ? ? ?

Dr. Lee :confused:

[britannic]

Sell it to a worthy DP member who will continue carrying the torch of the NA diesel, whilst you scorch rubber in Miami and blow the "Passed and Curious" crowd away in a haze of searing exhaust!!!! :D :D

[dieselcrawler]

Dr. Lee: why you holden' out on the N/A diesel? Just wondering...
Y'all won't have to twist MY arm to hard, I'd drop a turbo on in no time... if I knew where to start. I'd like to retro fit something off a 6.5L if I can, I need to keep things low-buck if I can. Matching parts and pieces together doesn't bother me, if I know I got the right parts to start with... Any ideas?
Didn't have a chance to brave the cold night air tonight to work on the ol' 'Crawler, but I hope that fixing the fuel leak might cure my problem. It's leaking after the lift pump, at the boxy lookin' fuel filter mounted on the fire wall... I think I may have installed the fuel filter wrong, or messed up the seal on one of the 4 tubes that it goes over. I'll start by looking at that, but with all the stuff around that area, actuly seeing the bottom of the filter is difficult. Doubt it's the problem tho, it was acting up before I changed the filter in the first place...
Greg, AKA DieselCrawler

[dieselcrawler]

Oh, I forgot... Dr. Lee, my truck see's full throttle often enough, I don't think runnin' the ol' beast any harder would do much... **grin**
and thanks for postin' the pic of my truck...
Greg

[dieselcrawler]

Hey all, I finnaly got a chance to work on my truck a little again today, tryed changing the fuel filter, hopeing that it might be where the leak was coming from. Found no damage to the seals, but put on a new one anyway, useing a little grease around the post or tubes that the filter goes over, and it STILL LEAKS... reguardless, it seems to be running ok, and started right up, both cold, and after changing the filter once it was warmed up. I guess my question is this: are there ports or any other place fuel could leak on the back or bottom of the filter holder houseing? I didn't have time to remove it today, I hope to have time to do that tomorrow. It only leaks when the truck is running,and it's a steady drip, coming right off of the fuel filter houseing, just can tell where it comes from. Any ideas? Thanks in advance,
Greg

[britannic]

The pressure sensor and drain cock seals are real problem spots for leaking on the FM80. I ended up upgrading to an '97 vintage FM100, when I found it really hard to get the seal etc. No problems with leaks anymore and the filter is really easy to change. The FM100 comes up on eBay occasionally and I got mine for $47.00 plus S&H from there.

You can remove the pressure sensor and plug the hole with epoxy.

[dieselcrawler]

Ok, so here's how it went... I took the fuel filter/houseing off the truck, removed the filter, and cleaned everything off. I removed the vacuum switch, and pluged the hole with JB weld, let that set up, and put it back on the truck. No leaks, and the truck seems to run ok... didn't drive it much, just a few miles, topped off the fuel tank with fresh fuel, and will drive it as I can over the next few days, and see how it runs, and if what I have done has cured the problems. Thanks for all your help, any who posted answers, and I'm sure I'll have more questions and comments as time goes by...
Greg