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Discussion Starter · #1 ·
Trying to get this dually right. Figured I'd post my progress here as you all are more knowledgeable than me and might be able to help.

My annual search for a winter vehicle has resulted in another bad decision. I've been looking for a 90's or earlier truck with some towing capability to drive this winter and as a bit of a project. Being in New England, I don't want to drive my 128i in the winter. My search ended with this, very rough, 3500. I've wanted a GMT400, dually for a while. This just wasn't what I imagined.

Its been spray bombed flat black. Its got a single rear wheel bed. The interior is in good shape but filthy. The glow plug light isn't even coming on. The obnoxious exhaust is hung with wire. And the previous owner claimed it had a fuel delivery issue. The two hour drive home (yes, I'm dumb enough to try drive this home) proved that the "fuel issue" was in fact the transmission. I couldn't replicate it on the test drive but it won't shift into overdrive. It needs a lot of help. But, to try justify my bad decision, it is nearly rust free. It actually seems to run pretty well. And it was cheap.

I started my project by not looking into why my truck wasn't running great and instead cleaning.
The interior was filthy. So much dog hair...



I actually managed to get some of the stains out. Or just scrubbed them in deeper. Looks cleaner anyway. I'm not a dog person so I'm sorry to those that are but I just can't understand why you would want a dog in your vehicle.



Much cleaner. Doesn't feel gross inside at least. I'm going to vacuum the stuff the scrubbing pulled out and call it for now.
Now that I finished the part that wasn't solving my problems I pulled the codes from the OBD1 port. I got DTC 17, 18, 35, 78, and 88. I thought there were a lot more when I checked before buying. I have to dig into it more but the first thing is checking grounds which could contribute to all of them. There is also lots of wiring hackery going on.
When I pulled the truck into the shop it started stumbling. It ran fine for a two hour drive but now its having issues. Admittedly, that got me thinking about the fact that I could swap in a 6.0 LS and be in under my truck budget. Its financially viable I'm just not sure I have the skill to get it done before winter.
 

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I used "Formula 409" to clean seats and carpet. It took out some black engine oil stains.
Usually the first thing I do besides a real good visual looking over is cleaning. It can tell you some of the trucks past.
 

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6.5 Diesel to gas LS swap will cost you far more in time and money than you think. Nothing is the same between diesel and gas.
All your codes except 78 relate to the IP.
Check. PMD going bad? Electrical Filter on the optical sensor? Bad wiring/ connections/grounds.
Read thru the 6.5 newbies, and 6.5 FAQ, stickies on the top of this forum.
 

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Discussion Starter · #4 ·
Trying to work through the FAQs. Started with the grounds and finding lots of bad wiring.
I spent way more time than expected cleaning the grounds. I just wanted to confirm that they weren't contributing to any issues while I'm trying to diagnose the current problems. The frame to body and frame to engine grounds were pretty filthy but, as should be expected, cleaning them didn't result in any immediate changes. I cleaned the rest of the engine bay grounds also. I came across more strange wiring. Any suggestions or thoughts on the below photos would be helpful.
First, there's this loop of wire that was attached to the (lift pump?) relay on the firewall. But it starts at the battery power bus bar. So basically battery power going straight to the firewall? Also, on the other relay screw is a ground strap to the intake manifold that I don't believe is stock.

A connector behind the AC compressor that I can't find any place to connect it. Any ideas?

And then there's a wire coming from battery power on the alternator, the yellow one running along the wheel well cover, to a fuse box with glass fuses on the firewall that has no other connections. I assume none of that is stock? Also, you can see another previous owner ground strap from the frame to the engine made from three braided red wires. And the injection pump ground has been moved to the intake manifold because the screw is stripped on the pump. That shouldn't cause any issues other than being ugly?

A few other things, the CDR is filthy on the outside, probably should just be replaced? Also, I have a suspicion that the fuel cap is from a gas truck and is creating vacuum in the fuel tank that is causing the difficult hot starts. Lots of things to look into.
 

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Discussion Starter · #5 ·
Alright, still nothing too exciting. Started working through the wiring. Glow plug relay is working. And the truck cold starts great. So I think the lack of a glow plug light is actually the light itself or the wiring to it.
The coolant temp gauge always reads zero. Grounding the wire does not change it so its wiring or the gauge that is causing the issue. The odometer is also not working. Eventually I'm going to have to pull the instrument cluster and sort all those.
I also found more things I missed when I bought the truck or haven't mentioned yet. The exhaust is actually a decent setup. The crossover is 2.5", the downpipe is 3", and its a 4" straight pipe back. It does have an obnoxious 8" tip but its kind of funny so I'm going to leave it. It needs at least one more hanger and the clamp on the turbo is really loose but those should be easy to solve.
I realized I have an aftermarket lift pump. Looks like a Carter? So I don't really have any reason to upgrade that.

The fuel lines were messed with when the previous owner installed it. The return is leaking a bit. Hopefully I can just throw another hose clamp on it and that will be solved. They used clear fuel hose. Hopefully it holds up to diesel fuel?

I started ordering all the maintenance and reliability parts and went back and forth on getting a Fluiddampnr. The harmonic balancer doesn't look bad in my opinion but the rubber is swelling a bit. Should I just replace it?

Someone replaced the transmission cooler lines with braided stainless.

And the power steering pump looks empty. Granted its not hot.

Also, the front suspension is also in need of some work. The driver side sway bar link rotted completely away.

Parts are on there way now so hopefully some actually interesting progress coming.
 

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Discussion Starter · #6 ·
Made a bit of progress you can actually look at. The truck runs and drives. Maybe not great, but it does. But to actually take it on the road legally I need to sort some of the non-mechanical things. The first was the mirrors. They only had two of the three studs so they bounced around a lot. I just got a bolt that fit the threads for the missing stud and used that with a couple washers to fasten the mirrors.
Next was the exhaust. It was rattling around and swinging wildly. The obnoxious 8 inch tip was wired to the frame.

A quick inspection revealed a stock hanger that did not have a hanger on the aftermarket exhaust.

Terrible picture. You get the idea. I used some 1/2" rod and made a passable hanger.

With that, the exhaust isn't resting on the cross members anymore and I could get rid of the wire on the exhaust tip.
Next, an obvious issue is the lack of dually fenders on my dually. Before I can even sort those out, the bedside supports are missing from the bed for some reason. The bedsides just swing around wildly. I'm taking measurements off my dad's truck and welding tabs to some 1/8" rod to make the supports. I've only finished one so far.

So, 3 more of those and then I can figure out the dually fender fastening.
Meanwhile, the truck continues to offer more work. After sitting for a few days in the shop, a puddle of ATF appeared on the floor. It looks like the shift selector shaft seal is leaking.

So now there's that.
 

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Check the GLOW fuse in the fuse box.
Make sure it has voltage when the glows are glowing.
Check the ground just above the DLC.
 
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Discussion Starter · #8 ·
I was gone last week so just got back to it on Monday. Finished the bedside supports. Seem to do the job. Probably should have used something more substantial than 1/8" rod but I'm leaving it for now.


And started test fitting the dually fenders on the passenger side where someone already drilled holes in the bed.

So thats next. Getting those figured out.
 

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Looking great👍
 

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Like to see an old 6.5 gettin fixed up.....good work! (y) Btw, that tailpipe tip is kina obnoxious. Lol
 
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Discussion Starter · #11 ·
Little more progress. The fenders I have are missing the studs or bolts to mount them for whatever reason. My very elegant solution was to JB Weld M8 bolts into the existing holes.

And with some precision adjustment of the existing holes in the bedside, I have one fender actually fastened to the truck.

Not a whole lot different from the mockup picture but much more satisfying. Now to transfer measurements to the driver side, drill holes, and mount the other one.
 
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You have a pic in the first post of a connector behind the compressor. That looks like the high pressure cutoff switch. Someone probably replaced the compressor then realized they forgot to transfer the switch.

Looks like someone was chasing bad grounds, looking at the pics. If you question a ground, power the circuit up and check how much voltage you have on the ground. Should be no more than say 20mv. If you're looking at more voltage then starting looking for that ground problem.
 

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Make sure you cut the bed side. It should be cut back to about a inch from the fender well. That way when it squats the bed side wont hit the tires
 

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Discussion Starter · #14 ·
Make sure you cut the bed side. It should be cut back to about a inch from the fender well. That way when it squats the bed side wont hit the tires
Okay, that's good to know. Thanks. I haven't actually seen a GMT400 dually bed up close and wasn't sure if those should be cut.
 

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Kinda hard to get a decent photo that shows it.
Tire Wheel Automotive tire Hood Tread
 

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Discussion Starter · #16 ·
Some progress and some set backs.
Got the driverside fender mounted. Its not fit as well as the passenger side but its there. Need to cut the bedsides to the fender liners and make some kind of support for the outside of the fenders.

So that left fixing my transmission leak before I was comfortable driving it again. Fought with the shift selector seal. I got the tool because it looked like it would be much easier. Still wasn't easy. Probably my fault. New seal in, doesn't seem to be leaking for now. Also did a new filter and pan gasket.

I seem to be missing a cover for the flexplate and converter?
With that, I added some ATF and thought I should be able to take it around the block. And it wouldn't move. Not enough ATF, nice. Added the rest of the gallon. Still taking way too much revs to move and then it died. Started it back up and the check engine light is back. Same codes as before other than 78. It drove back into the shop still needing revs. I checked the fluid level. Low again. I'm an idiot and should have taken the shifting in place seriously. Going to grab more ATF today. Hopefully thats the only issue.
So, codes are back, still got to figure those out. Those are all injection pump codes. Should pull the electrical filter for the optical sensor. And I can't drive it until I get ATF. Figured I would tackle the glow plugs as I bought some new Duraterms. Looks like 9Gs so probably never replaced?

The connectors were all frozen to together.

So I'm replacing them with regular spade connectors.

But I didn't even finish those because I broke the plug on cylinder 7.

Cool.
So getting that out and more ATF are the immediate concerns.
 
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Keep a eye on regular spade connectors on the glow plugs. I tried it they wouldn't lock on. One slid off shorted to the frame and smoked my freshly built 10 gauge harness.
 

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Discussion Starter · #18 ·
This thing is really kicking my butt. Added ATF and went to start it up so I could shift through the gears and get the level right. It started but was much louder than usual and then settled to normal idle before dying. It almost started again but was louder than usual and now the Service Throttle Soon light was on. I cleared codes and removed the electrical filter for the optical sensor and now it won't start at all. I was able to confirm the APP has 5V and ground with a Powerprobe but wasn't sure how to get to the voltages when the connector was on the peddle to check the other inputs and outputs. Thats where I left it but a bit frustrating.
 

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Discussion Starter · #19 ·
Update: tried starting again tonight. Sounded like it might start but never caught. Now showing DTC 22, 25, 63, and 88
 

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Update: tried starting again tonight. Sounded like it might start but never caught. Now showing DTC 22, 25, 63, and 88
22-APP; Accelerator Pedal Position 1 Circuit Low
25 - Accelerator Pedal Position 2 Circuit High
63 - Accelerator Pedal Position 3 Circuit High
88 - Top Dead Center Offset Problem ( maybe be a bad CPS)

I would go through ALL grounds first then change out your pedal sensor if cleaning all the ground do not improve things
 
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