H1 Hummer Frustrations

Scott Owner Moreno Valley, California Posted   Latest   Edited  
Question
Electrical
1995 AM General Hummer 6.5L (Y L57) 4-spd (4L80-E)

It might be a long shot, but does anyone have any experience with these vehicles? Do you have any reliable part suppliers?

This has been a frustrating vehicle and one that I regret taking on. I fix one thing, and something else comes up. I put parts on and they are crap, so I have to find another source. I buy parts and they are not correct, so...

The vehicle had been sitting for awhile due to not starting. Between the battery connection problem, the fuel pump and power to the pump, the neutral safety switch (had to put it in neutral to get the engine to crank, sometimes) - how many friggin' things can be wrong with a vehicle?

What I'm left with now is a coolant leak from one of the hoses - I'll match something up - and the vehicle does not shut off when the key is rotated to the off position. This is a civilian H1, GM 6.5L mechanical diesel, with 4L80E transmission. I'd look on a wiring diagram, but the information I have is poor to say the least. I'm thinking ignition switch, but other than the fuel pump I'm not sure what keeps this vehicle running. Measuring voltage at the fuel pump with the KOER I see charging system voltage at 14.2 volts. Turning off the key, the voltage at the pump drops to 12.95 volts the engine continues to run for 5 - 20 seconds. Touching the wiring harness where the ignition switch comes out of the column usually gets it to shut off right away. Any thoughts?

Oh, there is something else. He wanted the vehicle serviced, so a transmission service was done and DEX VI was used, There's now a leak when it sits which is in the front pump/seal area, :-)

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Michael Owner/Technician
Tampa, Florida
Michael Default
 

back in the day Alldata had info on those you just had to call and get fax they never had them on the disks

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Jim Owner/Technician
Charlotte, North Carolina
Jim Default
 

There should be a fuel cut off solenoid on the injection pump- check either stuck/ leaking, or still gets power when keyed off.

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Scott Owner
Moreno Valley, California
Scott Default
 

Thanks for that Jim. I do have the H1 Hummer info on a PDF file, but it's difficult to make out and it goes across multiple pages, the way diagrams used to be drawn back in the day. I think GM used a company starting back in the 80's called Valley Forge that drew individual cells. I was a big fan as I hated going across multiple pages to see a injector pump - Some people must like them though as…

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Jim Owner/Technician
Charlotte, North Carolina
Jim Default
 

Yes, that is what should kill the engine as soon as power is removed, is it 12 or 24 volt system? Lot's of these got swapped around and ended up with crossed part numbers.

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Jim, It's 12 volts. Would this be what I need? store​.​adv4x4​.​com/5742632​.​html There's a single wire, appears to be 10 gauge that has voltage (13.6 volts) KOER and 0 volts as soon as the key is turned off. That solenoid sits under a cover. How difficult is that to remove? Thank you!

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi Scott. Yes, that appears to be the correct shutoff solenoid for the mechanical Stanadyne injection pump that sits under the governor cover. The cover has a square cut seal in a groove and the threaded studs have square cut seals where they pass through the cover too. There are two solenoids under the cover. The fuel shut off solenoid is the one in your photo and the other solenoid is the HPCA…

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Believe it or not, I actually remember that wire to the injection pump was "54A" on the actual military models. :-) That does you no good whatsoever, sorry. I was USMC from 1990-94 and the real ones were my lifesblood. They had just released the first civilian models before I got out. The real ones were all built in 1986. Never saw one not shut-off so no doubt yours is quite different than all…

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

When I got out of the Seabee’s I worked civil service for about 10 years. We worked on a lot of Hummers. I remember fighting oil leaks for a Marine Reserve Battalion, we would fix them, they would take them out and bring them back leaking! Finally I overheard one of the Marines telling one of my technicians “On a good downhill run, these babies will almost hit 80 MPH!!! No wonder they were…

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

It would have to be one helluva hill and they would have to be in neutral. They were governed at 45 MPH. At least the ones real Marines used were. IDK what sorta rijajig modifications some reserve unit might have gotten away with.

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

These were early model, probably 1989-91. they didn’t have a governor that I remember, but top speed on a good day was about 55 MPH. and that sounded like a jet engine taking off.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

All of ours were 1986 builds. First run from my understanding. There wasn't even a distinction yet. When I read about things that were different later, I figured they had to build more eventually.

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Top speed for civilian model H1s was limited to 83 MPH Geoff.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Jamey: My ex was a Mechanical Engineer for the Navy. She did Ship Survivability. She used the Marines to break things. Back in 1996/97, they were trying to use tablets with hand-holding (guided diagnostics/prognostics) for maintenance tasks. Didn't work out too well. They couldn't make it Marine-proof. (At the time, GM was using the Army [TAC]. During a conversation with her in Plano, the…

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Jamey Owner/Technician
Ventura, California
Jamey Default
 

Very few things are Seabee or Marine proof! We can break a bowling ball with a powder puff!!

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

No Marine is ever going to take as good care, of anything else, as he does his primary weapon. It goes against our core (Corps...lol) programming. Btw, are you sure you meant 96 not 2006? We had books, microfiche, and a desktop running DOS, in 1994.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Geoff: I meant the dates stated. Her NAVSSES department (now called Naval Sea Systems Command: Naval Surface Warfare Center: Carderock Division: Philadelphia Division [or NSWC Philadelphia Division for short) was Ship Survivability. All of that stuff has been moved to West Bethesda, MD after a couple of different Reorgs. Landlubbers like you wouldn't have had much to do with what she was…

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Brad Diagnostician
Pullman, Washington
Brad Default
 

I suggest you dump a bunch of gasoline in the cab and light it off!!!! I don't have any real good literature on this turd either. However if you can wiggle the wires at the switch and it shuts off it would be a good bet that the switch is fuggazzi. You might be able to build a K2500 Suburban or such in AllData and look at the power distribution diagram and see if it is somewhat close to the H1…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Brad, The lighting this thing on fire is tempting. I've set a new record as this has been here for 6 months now. To say I'm done does not do justice to the way I feel about this.

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Zachary Mobile Technician
Austin, Texas
Zachary Default
 

Hello Scott. First off I want to start by saying I feel your pain. The last shop I worked for had two customers with those at one point and they are a freaking nightmare always. We used to get most of our parts from a company called Adventure Accessories. As I recall it was pretty much always OEM stuff. Not sure if they are still arpund but I believe they also had access to wiring diagrams and…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Zachary, Adventure Accessories is still around. I got the auxiliary heater/HVAC case from them. Unfortunately the case they sent out was for a 1997 and later...I wasn't too happy about that. I did look on the PDF files for parts and found the lower case on eBay. That was another adventure as the customer had bypassed what he thought was the rear heater core, but it was for the front. We put…

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

My first thought, "volt drop" Have you tested?

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Albin, I have no experience with the 5.7, 6.2, or 6.5 GM diesels - but this is different as this does not use any electronics for the engine. There is a DLC for the transmission, which is a 4L80E, and uses a TCM, but... I did do voltage drop testing on this when it first got here. The engine barely cranked over and fixing the corrosion at the battery terminals, replacing bolts took care of…

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Allen Owner/Technician
Dallas, Texas
Allen Default
 

Jim lynch. Adventure accessories … dennis jankowski cadillac of nova? … I might have a # of an h1 tech p.m. Me I'll check. Allen

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Allen, I did order a part from Adventure Accessories - store​.​adv4x4​.​com/5745033​.​html and this turned out to be a case for a 1997 and later H1. There must be a cataloging error, but I figured it was money thrown away. I never bothered to call him back, but maybe I should. I'm so frustrated with this. I'm not sure why these have such a high resale…

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Allen Owner/Technician
Dallas, Texas
Allen Default
 

Scott, I used to work on these back in the "day"; there were multiple upgrades on the a/c systems inside and out, so its hard to say and order by vin/year if you can get #'s off the old parts that sometimes helps, or the orig parts are not available and you have to modify/make work. "Custom" = $$ yeah they can be a bitch! Charge your time; it's hard to find people who will even touch them…

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Scott: Is this you? hummer-hmmwv​.​tpub​.​com/TM…HTH, Guido

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Guido, Supposedly the PDF file I posted above is from AM General and although the diagrams are not really legible they do not look like what you posted. I'm leery of running anything that wants to me to click "Run" and it looks like they want to install malware - support​.​google​.​com/chrome/thread… Thank you though.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Scott: I don't blame you for being leery. I don't see anything like that. (What can I say? I'm a very trusting individual.) I did run the url through virustotal before posting and it came up clean. See if you can zoom this enough. HTH, Guido

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Hey I dont know if the Hummers were made by AM General in 1995 or not but I'm sure they were. Anyway I had an early 2000s H1 a few years ago with an air suspension problem. Not that it matters but I live real close to the AM General manufacturing plant in Mishawaka IN. I just called them directly last time and they emailed me diagrams. Hope that helps.

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Chris Technician
San Diego, United States of America
Chris Default
   

You also want to check the voltage across TPS, the GPC and the OPS....ias for the the NSS, you can start the rig by holding the shift lever towards your knee as you crank it over. The NSS can be bypassed/jumped. Or can be replaced by a surplus switch (not ment for a NSS).I think it's a parking switch locatedon the same shifter assy but it works..its the same switch and doesnt cost an arm and a…

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Chris, I appreciate the response, thank you. The P/N switch was replaced and that problem was fixed. The fuel pump I spoke of was the lift pump as you correctly stated. Somewhere in this thread I mentioned I had replaced the pigtail and the EOP switch to get the pump running. As far as switching from DEX III to DEX VI, I made that decision as GM designed this fluid to backwards…

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Chris Technician
San Diego, United States of America
Chris Default
 

No worries. Mike Sabresse is the head tech there. I think the idling and starting probs are likely a combination of the throttle position sensor, oil pressure switch, glow plug controller and lift pump due to age. And I wouldn't doubt the optical sensor of the IP would need to be looked at. How many miles on her? No MIL codes? In regards to DeX. Yes, they do mention its backward compatible BUT…

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Scott Owner
Moreno Valley, California
Scott Default
 

Thank you for your service Chris and thanks for the name! I appreciate it! I texted my friend and the ESO said he's a great guy. :-)

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Martin Instructor
Burnaby, British Columbia
Martin Default
   

Hi Chris. I worked on a number of civilian Hummers of that vintage at a GM dealership and some still had 6.2L engines, while others had 6.5L engines, both with the DS 2 mechanical distributor pumps. I've also seen them retro-fitted from electronic to mechanical distributor injection systems, which required electronic lift pumps, since the 6.5L engine block for electronic injection systems did…

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Scott Owner
Moreno Valley, California
Scott Default
   

Hi Martin, To borrow something from Jon - you're my new hero. Early on with this vehicle I discovered a 16 pin DLC connector, but as it turned out this was for the 4L80E only. It was about that time - I realized I might be in over my head on this vehicle. You are correct this is a DB2 mechanical distributor injection pump. Chris pointed me in the right direction with -…

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Martin Instructor
Burnaby, British Columbia
Martin Default
 

Hi Scott. I'd happily have passed on the H1s too! Nearly every one of the 20 or so H1s that I got stuck with working on had wiring that was very poorly routed and connected around the "dog house" area. I'm glad that you have it handled. You are correct on the DLC. On the old G vans with the mechanical DB2 pump through '95 MY, the ECM was under the drivers seat inside the metal seat base…

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