m1008 lacking power at full throttle

[meat27]

My all-stock '85 m1008 is lacking power beyond half-throttle. It runs fine from zero to half-throttle, but opening the throttle any more than that acts like fuel starvation. It wont put out any black smoke even at full throttle. If I push the pedal to the floor, the engine "bogs" until I lift about half-way off the throttle...then it resumes moving the truck normally.

The air filter is fine. I just changed the fuel filter (tin rectangular one on firewall) but the problem got no better.

Anyone have any thoughts as to which direction I should be looking next? A fellow at the parts store mentioned maybe the governor in the IP being worn-out. I'm a mechanic, but hardly any experience with diesel fuel systems.

 

[hre513]

You may want to check out the TM. Start off simple and work your way up. No restrictions in the fuel line? Fuel pump working properly? Lastly may be the injection pump.

 

[Barrman]

It shouldn't bog, but every 6.2 I have ever driven seems to stop adding power about 1/2 throttle. So, there really isn't any point in pushing down that far. Maybe all the ones I have driven have problems too?

Do as posted above. Fuel supply, fuel filter and air filter. After that it is messing with the IP.

 

[USAWEAPON777]

It shouldn't bog, but every 6.2 I have ever driven seems to stop adding power about 1/2 throttle. So, there really isn't any point in pushing down that far. Maybe all the ones I have driven have problems too?

Do as posted above. Fuel supply, fuel filter and air filter. After that it is messing with the IP.

Yea thats how my cucv is past half doesn't give a lot but it does give some. Also he has to push it to the floor if he wants a downshift. like everyone else said make sure your getting adequate fuel and air. hopefully its not the ip since as I recall their very expensive to rebuild. But if it works fine till half throttle Im thinking some sort of restriction somewhere.

 

[Warthog]

Make sure you download the free technical manuals.

They are free at JATONKAM35s HOME ON THE WEB

 

[epitts]

I don't if this will help but check your fuel return line.

 

[cucv1833]

My m1009 does the same thing but i think thats the way it is. It runs great and gets up to speed (65mph) no problem
but if you push the throttle down suddenly it wont make any power. if i ease into it will make plenty of power.
I suspect a I.P. rebuild in the future though i had a liitle debris in my fuel return valve.

 

[WARWAG]

Well thats a problem for sure since it actually bogs. Like everyone else said try your TM. Let us know what you find. Im sure it will come up again for someone else. Threads like this help other people down the road. Wish I could help you more.

 

[meat27]

TM stands for "technical manual" correct?...Thanks a ton for the link to the manuals, I'll be getting into them shortly.

I am for sure having an issue of some sort because the full-throttle bogging wasn't present before the 400 mile trip home a couple of weeks ago, or at least it wasn't as drastic. I remember driving on the interstate and being able to get a little black smoke from the tailpipes when I fully opened the throttle. No black smoke any time now

I guess I'll need a pressure gauge to test the lift pump? When I changed the fuel filter, the lift pump had no problem priming the new filter swiftly, but I guess that might not be enough of a test to verify that it's 100%.

I reckon its gonna be checking for restrictions in the fuel lines and then on to some IP work. It looks like I might be learning the procedure for installing one of these IP's. Anybody ever tried to rebuild an IP at home?

 

[Matt65]

Yes, TM= Tech. Manual found here: http://www.jatonkam35s.com/jatonkaCUCV-TMdownloadpage.htm

My understanding is that the DB2 does not use a lift pump in some applications. Meaning that if you have a good prime to IP, and NO leaks, the Mech Pump should not decrease performance on flat ground. -Just my thinking

Rebuilding the IP does not appear to be particularly hard, but requires a lot of specialized equipment to achieve correct output/performance.

Im no expert, and have not read the TM on this condition, but I would check:
Confirm good fuel
Fuel Filter, replace if needed.
Injector Cleaner.
Tank pickup sock (as almost last resort)
IP Rebuild (as last resort)
Check for IP leaks in Engine valley beneath the air filter.
Check Airfilter, replace if needed.
Is the throttle linkage moving freely, to full.

Tim @ Accurate is who did my pump rebiuld.
http://accuratediesel.com/

 

[Warthog]

TM stands for "technical manual" correct?...Thanks a ton for the link to the manuals, I'll be getting into them shortly.

I didn't say this earlier but Welcome to SteelSoldiers.

Make sure you visit the Cucv Wiki - Steel Soldiers::Military Vehicles Supersite (CUCV Wiki) that is at the top of the page on the CUCV Forum. All of the CUCV Technical Manuals are listed and many other helpful bits of information.

You need to download the repair manuals. You can get then for free. A couple of our members have posted them on their websites.

www.jatonkam35s.com
www.liberatedmanuals.com

The wiring diagrams are in the appendix of the -20 and -34 manuals.
Also checkout the CUCV stickys. It is where we try to post helpful tips and tricks.

Almost every question you will have has been asked and answered many times. The advanced search will become your best friend. Please don't hesitate to ask something that you can't find.

Read the TM 9-2320-289-10 Operators Manual to find out how a stock system should work. It is simular to the Operators Manual for Civilian vehicles. It tells you where all the lighs, switches, etc are located and what they do.

Three of the most important tools you can buy are:
Digital Voltmeter and know how to use it - ~$10 and up
12v Battery Charger - ~$50 for a decent one
Battery Load Tester - ~$30 for an okay one at Harbor Freight

As far as rebuilding the IP, like it has been said, the required equipment to calibrate it is VERY expensive. You can have it rebuilt for ~$300-$500. Alot less than the thousands for the equipment.

 

[DokWatson]

TM stands for "technical manual" correct?...Thanks a ton for the link to the manuals, I'll be getting into them shortly.

I am for sure having an issue of some sort because the full-throttle bogging wasn't present before the 400 mile trip home a couple of weeks ago, or at least it wasn't as drastic. I remember driving on the interstate and being able to get a little black smoke from the tailpipes when I fully opened the throttle. No black smoke any time now

I guess I'll need a pressure gauge to test the lift pump? When I changed the fuel filter, the lift pump had no problem priming the new filter swiftly, but I guess that might not be enough of a test to verify that it's 100%.

I reckon its gonna be checking for restrictions in the fuel lines and then on to some IP work. It looks like I might be learning the procedure for installing one of these IP's. Anybody ever tried to rebuild an IP at home?

Black smoke isn't a good thing on a naturally aspirated 6.2 diesel, its unburnt fuel. My pump is turned up, and I barely get a smokey haze at full throttle, 4 low 1st gear. Sounds like you had fuel issues before it started bogging.

 

[meat27]

Thanks for the warm welcome and all of yall's advice. I am LOVING this truck, and if I end up having to get the IP rebuilt, I'll know I should have lots of reliable miles ahead.

I am going to do a little homework with the TM, but judging from Matt65's checklist, I'm down to either a restricted fuel tank sock, or a failing IP.

 

[meat27]

Well I've got it FIXED!!

I checked all the other stuff and had no where else to go but an injector pump swap. I still had my doubts as to the IP being the ultimate problem, so I bought a used pump off ebay for about a 100 bucks. I swapped it in and the truck is running normal again through the entire throttle range.

Thanks for all yalls help!

 

[Matt65]

Very good glad to hear shes running. Thanks for the update.

 

[meat27]

Well, the truck is running much better throughout the entire throttle range with the new IP, I'm happy about that.

But, I still have an issue with the fuel system losing its prime sometimes when the truck sits for a while. I've read where others have found leaks around one of the sensors on the block where the fuel filter mounts. Anyone else experienced this?...or have suggestions on where to look first?...have a feeling this one might be tricky b/c there are no visible external leaks.

 

[Matt65]

How do you know it's losing prime..fuel pressure gauge? Cheap electric pusher fuel pumps are popular during startup for these trucks, of course that just mask the symptom of the rootcause.

Sometimes what seems like lost prime could be bad Glow Plugs. I'll admit, I thought the same about my truck. Until I found 7/8 plugs bad! There is a good write up in the TMs. The resistance from GP terminal to ground should be 1-3 ohms iirc.

I'd check the engine valley at the IP throttle shaft seal mine was leaking there before the rebuild. The IP return valve may be worth looking at.

 

[meat27]

Well, I havn't put a gauge on the fuel line to verify prime loss, but thats just what I'm figuring. The glow plugs are nearly new. And, each time the truck has done this malfunction, the engine has initially started up fine...it just died after 5-10 seconds. That's when I had to crank and crank to restart...just like I do after a fuel filter replacement.

Tonight I did find the fuel line clamps on the filter block to be not very tight. I snugged em up and I'll see if maybe that helps.

My fast idle solonoid hasn't been funtioning. I found the wires unplugged from the engine sensor. I reconnected them and will have to wait til tomorrow for another cold start to see if it'll be working now.

Call me crazy, but after the IP swap, at 60-65 mph, the HOWLING sound made by the engine sucking air through the breather is MUCH louder than before the IP swap. I have no idea why that noise level increased.

 

[Barrman]

Loose air cleaner housing maybe?

 

[meat27]

....that was my first suspicion on the noise so I pulled over to check and found it not loose. I'll look it over again today.