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6.5L Turbo Diesel Hummer H1 1999 - Erratic RPM and throttle problems

S

slowbutsteady

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Location
Niagara Falls/NY
The engine runs okay at idle (600 RPM). At high idle the vehicle sounds like it is missing and the engine shakes and rpm sways from 1200 to 1500. The vehicle is not drive-able. The throttle is very touchy and can jump rpms from 1800 to 2500 and race. It seems to be able to manage max rpms so there is some control. I've seen others have had this problems but rarely do people seem to post the solution. I will take the time to do this as this H1 is my daily driver and I am stuck until fixed.

The problem got worse over a period of a week. At first it occurred a bit after start up. Then the RPMs swung a bit (about every 4-6 seconds about 10%. Now the swing is so great that the vehicle takes off to 50 MPH and then drops to 30 then back up to 40 and all over the place. The same thing happens (erratic rpm) i I leave the vehicle in Park and select different idle speeds.

So far I have:

1) Cleaned the air filter.
2) Checked the fuel filter.
3) I connected a 1/4" clear hose to the return line on the IP and there were no bubbles. Good fuel flow and it was clear.
4) I have pulled grounds, cleaned and tightened.
5) I am about to check optical sensor on IP or put an oscilloscope on signal lines to look for problems.
6) I checked the system data from a logger (ScanXL Professional) and I don't see any bad sensors.
7) The engine is reporting no error codes.
8) I tried another FSD (relocated, D-type) and same issues.

I will check the fuel pressure tomorrow and return line pressure.

I'd like not to replace the IP unless necessary. I can try to swap the ECM. I'd like any input on what I could look at that could explain the problem.

I will share what I find here and any signal waveforms if you have suggestions. This is the most annoying problem yet.
 
Welcome to The Truck Stop.

There are some differences between the pickups and hummers, but I believe you have the same throttle pedal assy as the pickups do. That is what I would be checking next. I have a db2 and mechanical cable, so I am cannot verify it. iirc it is called the APP. I am horrible at searches, but if you go into the search bar at the top right of the page and search there, you might find some threads.

Stand by, there are way smarter folks than me here, someone can maybe have a more specific answer.

My hummer is my dd also, as soon as I put a new seal in my right front geared hub... back up 3rd car for the wife and I getting a few miles on it the last month.
 
Could be the APP but in most cases it will drop a code if any of the three signals are mismatched. To me i favor the trace with the oscilliscope on the optical sensor output and then also on the processed combined signal to the PMD from the PCM. I am almost leaning towards a cold solder joint on the PCM or a intermittant connection in the Optical Sensor> PCM> PMD wiring.
 
Update: For anyone having the same problem. The solenoid closing time was 0. I found the solenoid on the injector pump was shot and partially shorted for the FSD was unable to detect the closing time.

I had to replace the injector pump. What a horrible job.
 
Dang. Well, at least it's fixed now and with any luck you should not have to play with that again for a long time.

Hopefully you have a over the fender style creeper? If not something to consider, My last house I had a shelf with a piece of 3/4 ply I had rigged for quick use, not an option in the new home. I just found the one I am ordering -
http://www.amazon.com/gp/product/B002Y090BY/?tag=jhuntlink-20


Do you run any additives, biofuel, etc. in your fuel? How many miles on it?
Everybody likes pics of a cool truck-hint hint.
 
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Will L. said:
Dang. Well, at least it's fixed now and with any luck you should not have to play with that again for a long time.

Hopefully you have a over the fender style creeper? If not something to consider, My last house I had a shelf with a piece of 3/4 ply I had rigged for quick use, not an option in the new home. I just found the one I am ordering -
http://www.amazon.com/gp/product/B002Y090BY/?tag=jhuntlink-20


Do you run any additives, biofuel, etc. in your fuel? How many miles on it?
Everybody likes pics of a cool truck-hint hint.
Click to expand...

I did not have a fender style creeper. After working on it for hours balancing on various things, my friends and I constructed industrial racking on the front of it and used a 4x8 sheet of plywood to lie on. It was still quite uncomfortable to do the work like that.

I believe I will order the one you found too. Let me know what you think of it when you get it!

I have not run any additives. I use to add a lubricity additive last year. The vehicle had 30,000 miles on it when I got it in Dec 2012. I've put 30k on it since (it is my daily driver). I drive it hard and it is an amazing ride. It has been a PITA for maintenance and school of hard knocks.

Ive had to replace a geared hub (tire came off when driving it). I've replaced the shocks, brakes, pitman and idler arm, all ball joints, had to rebuild the ABS module, FSD (of course), now a new IP pump, I had to rebuild the rad when the engine *decided* to chew it up. That included a new fan. New lift pump and oil pressure sensor.

I believe the IP died because the fuel pressure was very low. I am annoyed about the fact that something like a lift pump can go and there are no sensors to detect it. I'm adding fuel pressure sensors for supply and return.

I bought a VE351 turbo but haven't had the time to get into that project yet. I still have to replace the harmonic balancer & pulley tomorrow. I'm hoping there isn't too much more that can go wrong on it. I have installed a boost and EGT gauge so I don't melt pistons. I'm keeping boost under 11psi until I can order a thicker head gasket and studs.

Fuel mileage hovers around 10MPG. IMAG1438.jpgIMAG1440.jpgIMAG1447.jpg
 
As an Amazon Associate we earn from qualifying purchases.
Sounds like your on the right track- daily driver, nightly repairs. Been there, and not just with the Hummer. Did you do the clear line on the 4" long return from ip to metal line to help with future diagnostic, if not throw it in now. Also put in a tee just before the ip for the fuel pressure gauge. That's where you need to see the numbers to save the ip next time.

Interested In the turbo swap, please do a write up with results. Are you going to increase exhaust when you do it?

My mileage is 10.4 before and after turbo, just quicker now. If I keep my foot out of it one of these days I'll see what it could be. Maybe 11?:hihi:
 
Will L. said:
Sounds like your on the right track- daily driver, nightly repairs. Been there, and not just with the Hummer. Did you do the clear line on the 4" long return from ip to metal line to help with future diagnostic, if not throw it in now. Also put in a tee just before the ip for the fuel pressure gauge. That's where you need to see the numbers to save the ip next time.

Interested In the turbo swap, please do a write up with results. Are you going to increase exhaust when you do it?

My mileage is 10.4 before and after turbo, just quicker now. If I keep my foot out of it one of these days I'll see what it could be. Maybe 11?:hihi:
Click to expand...

Tee in fuel line - that's what I am doing next. I'm in the middle (with friends) of replacing the harmonic balance at this moment.

For the turbo swap I am a bit concerned about the oil loop. The turbo has a strange gasket for oil cooling. I need to find an adapter so that I can connect stainless hoses. Have you seen anything that converts the turbo flange to fittings for hoses?
 
I helped a friend do a remote mount on his center mount. I took a piece of 3/8" hot roll plate, cut to fit and use the mounting bolts and the funky figure 8 o ring. Drilled holes and welded on npt fittings for the oil. 1/8" for feed and 1/4" for return. His was on a van, so moving his turbo up and back a little was not a big deal. Where to fit a good breathing turbo on a Hummer- idk. I was thinking about a roof mount ATT...twin stacks up either side of the windshield one for intake the other exhaust- turbo in the middle. Yes I'm a nutcase...
 
Time for a compression/leak down test. Are you just getting blow-by out the dipstick or oil fill? Is your upper radiator hose pressurized? Any blue smoke when running?
 
No blue smoke when running. Engine runs fantastic other than covering me with oil.

Blow by only on dipstick.

Upper radiator hose pressurized? How should I check that and when? (at idle?)
 
Radiator hose pressure wouldn't really be related, is more a test of head crack or gasket failure, just threw it in while I was asking. Idle is fine, you should be able to squeeze the hoses easily, not feel like they are hard with pressure.

I don't know anything about the Hummers, what is the same, what is different. Do you have the CDR unit, I believe it's "crankcase depression regulator"? That controls crankcase breathing, and removes vapor. When they go bad they can pressurize the crankcase a bit, which would look like increased blow-by. I know there is a test listed on this site somewhere, or on other 6.5 sites, to see if it's operating correctly.
 
CDRs rarely fail. They are spring loaded in the open position and closed by WOT vacuum. If your turboing a nat aspirated engine you might try changing to one from a turbo engine.
 
Thanks Ak. I'll do a compression test tomorrow and see how it looks. I does not look good as I tried to decrease the boost but it still lifts the dipstick and spits oil when RPMS are high with some load. I have not changed the Turbo yet so it is the original 6.5 unit.
 
For his 99, think 99 in a one ton, except gm6 center mount turbo is stock. Engine and transmission is the same as truck. Along with the compression test, do a leak down test like Dave mentioned.

If you want to see if the cdr is it, just bypass it with a piece of hose for a test run. You'll burn a little oil but that won't hurt anything. If the blow by is still there, bad cdr not the cause.
 
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