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350 to 6.5 harness

Landon730

Landon730

Active Member
Messages
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186
Location
Greenwood Arkansas
I’m swapping my 98 from a 350 to a 6.5. I have a 96 donor truck and my only question about it is do I need to swap the interior harness? Will the gauge cluster work with the existing harness? I know the engine harness will have to be changed but will it plug into the firewall with any problems?
 
Yes you need the ENTIRE harness swapped. The ecm is in behind the glove box and needs controlling.
The gasser has a fuel filter on the frame under the drivers door. This is where the liftpump is for the diesel. That harness is required there also.

The gasser has an intank fuel pump. Swap the tanks, and harness feeding it.

The only part of the harness you may not HAVE to swap is the last part that goes from the frame to the tail lights.

I don’t know 100% the dash has to change but I am 99% sure it does. You will have it all ripped out to do the harness anyways, so do it to be sure while you are there.

This is a major undertaking, That’s why almost no one does this. Good thing is you will see any problems throughout the truck as you go. Fix everything you can as you go. If you skip something you se now and have to go back in a year it will be very upsetting.

Read about and write down all the mods you want to donalong the way- like liftpump harness relay, or tank sock elimination, etc. Now is the time.

Take pics and notes. They can come in helpful in the future for you, and future owners.

Try not to damage the gasser parts coming out- you might make $ off them when done or along the way to pay for improvements, or at least asprin for the headaches it will cause. Haha
 
Will L. said:
Yes you need the ENTIRE harness swapped. The ecm is in behind the glove box and needs controlling.
The gasser has a fuel filter on the frame under the drivers door. This is where the liftpump is for the diesel. That harness is required there also.

The gasser has an intank fuel pump. Swap the tanks, and harness feeding it.

The only part of the harness you may not HAVE to swap is the last part that goes from the frame to the tail lights.

I don’t know 100% the dash has to change but I am 99% sure it does. You will have it all ripped out to do the harness anyways, so do it to be sure while you are there.

This is a major undertaking, That’s why almost no one does this. Good thing is you will see any problems throughout the truck as you go. Fix everything you can as you go. If you skip something you se now and have to go back in a year it will be very upsetting.

Read about and write down all the mods you want to donalong the way- like liftpump harness relay, or tank sock elimination, etc. Now is the time.

Take pics and notes. They can come in helpful in the future for you, and future owners.

Try not to damage the gasser parts coming out- you might make $ off them when done or along the way to pay for improvements, or at least asprin for the headaches it will cause. Haha
Click to expand...
I’ve heard how much of a pain they are that’s why I decided to get a donor truck instead of piecing it together. The dash is basically gone because of how busted up it is so I have no problems taking it out, just figured I would save time not pulling he dash but I’m not to bothered by doing it. I’ve worked on quite a few 6.5s so I do at least understand how it all works. I think the hardest part with be the harness swap
 
Basically EVERYTHING is different. On the next gen trucks it's a simple swap, but it's a massive undertaking on a gmt-400. That's why most go with a db2 mechanical injection pump because of how much is different. And I know the 2 trucks look virtually identical, but essentially 96 and 98 are almost different trucks with how much stuff changed between them.
 
THEFERMANATOR said:
Basically EVERYTHING is different. On the next gen trucks it's a simple swap, but it's a massive undertaking on a gmt-400. That's why most go with a db2 mechanical injection pump because of how much is different. And I know the 2 trucks look virtually identical, but essentially 96 and 98 are almost different trucks with how much stuff changed between them.
Click to expand...
I can go with the db2 pump but how do I get the tranny to shift? It’s a 4l80e. This 350 has a cable pedal like the db2 pumps so what’s making it shift?
 
My Dad gave me his 1943 Willy’s mb because he knew I would be the one to turn the wrenches, and becuase I would keep it like he did- fairly stock without getting all “classic car rules” about it, so then I and others could actually use it on some trails.

And here in Southern Nevada, DMV wont allow older parts on newer years of vehicles related to smog. So I couldn’t do it here (unfortunately). Truth is db2 can burn cleaner than ds4 when set up that way, or have more power. And can last longer with less repair costs. Just better, period.

If those are your reasons to keep ds4 and ecm then ok. Otherwise- HELL NO! Convert it- now!
 
IF you can get a DB2 to start it will run until:
1) You run out of fuel.
2) The engine blows up.
3) You loose 12v to the shut off (Well most of the time it shuts off.)

When you finally get a POS DS4 to actually run:
1) Was it a ground, the Dammed PMD, or the PMD extension harness?
2) Oh Wait it's still not fixed as the engine is running away or stalling again.
3) It fishbites just to test the CPS and OPS misfire detection.
4) the OPS hates any questionable dark fuel and will give you trouble over it. Like used engine oil to just a little air.
5) You have a spare $400 PMD setup and cable ready to go - always!
6) The Throttle pedal sensor, wiring, or ECM in the order of highest expense went bad...
7) You got winter boots and good shoes with a couple of Lithium battery flashlights in the rig for the walk you take often.

Electronics have improved the reliability of many vehicles over mechanical. The high current Piss Poor PMD design GM/Stanadyne used in the hot under hood environment was not an improvement, rather, it made things worse. A long ways off for second is the Dodge Cummins VP44 with electronics in the IP, but, it takes a lift pump failure to kill them.
 
Will L. said:
My Dad gave me his 1943 Willy’s mb because he knew I would be the one to turn the wrenches, and becuase I would keep it like he did- fairly stock without getting all “classic car rules” about it, so then I and others could actually use it on some trails.

And here in Southern Nevada, DMV wont allow older parts on newer years of vehicles related to smog. So I couldn’t do it here (unfortunately). Truth is db2 can burn cleaner than ds4 when set up that way, or have more power. And can last longer with less repair costs. Just better, period.

If those are your reasons to keep ds4 and ecm then ok. Otherwise- HELL NO! Convert it- now!
Click to expand...
In no way shape or form do I want ds4. I plan to use a db2 pump. Luckily Arkansas doesn’t have inspections so this puppy isn’t getting straight piped. I also have one quick question it’s way different but doesn’t deserve a whole nother thread. I went from smaller tow mirrors to the bigger style with different brackets and what’s could I use to cover up the holes in my door from the old brackets? Doors are to perfect to replace..
 
ak diesel driver said:
Ya know I have around 500k miles on a ds4 and they have been relatively trouble free
Click to expand...

That’s the exception not the rule in my experience. Some people break a million miles in a pickup. That doesn’t mean all or even most will. Most don’t make it half way there.

There is a guy in Vegas that bought one of the fleet trucks from us, a 92 that we were doing long term tracking on. He bought it with 350,000 miles on it. I gave him my cell and told him call with questions. He still does everytime he has an issue, and at just over 500,000 miles he lost the ip. I won’t say “db2 are good for 500k.” That’s the exception not the rule.

Having seen a couple hundred of these rigs pushed over the 500k range, ds4 dies out on average half way and the db pumps make it about 100k more.

Ownership is going to play a huge part in that. Proper filter changes, always good fuel pressue, always water free, solid electrical connections, nice lubricating fuel.

Now to be fair, that was without changing components of the ip. We sent them in for rebuild or replacement. Only in the last year I was at it did we start installing optic sensors ourselves. That was part of the peanut oil bio fuel disaster. So since we started stocking optics, we would then do that in house. It could be some or many of the bad ds4 pumps was just an optic. And as fuel continued to change since then current mixes might favor one design over the other altering what I learned back then. I believe the high pressure effects are different in how the atomization is now with alcohol in the fuel compared to before possibly lowering what was the optimum pop pressure.

Or, could be God just loves you more:)
 
Can you show pics of the mirror holes?

To be fair on the idea of get rid of the ds4 and replace with db2:
Search Bobbie Martins book on here on conversion.
I have a hatred towards the ds4 and pmd. Having had sommany issues with the system compsred to almost nothing ever with the db2 is why.

Being able to buy a tune for the ds4 does help if you run a big non wastegated turbo like ATT over it on a db2. Imo still not worth it because the money saved currently and future on pmd, heatsink, pmd cable, any sensors,etc. is easily offset.

Trans controller is a one time thing like ecm. If you have other 6.5 rigs with ds4 then keep the old parts. Otherwise well them to pay for the controller.

I also don’t like the gauge cluster in GM. I am an old school hot rodder. I like round gauges-more the merrier. I would sell the cluster, and put in gauges and just gonfrom there. The square body dash was the pinnacle of chevy dashes imo because it looked like round gauges everywhere. If you guys see a couple gmt400 running around with metal backing (and 1 out of wood) full of round gauges, those might be my handy work. The trick is to attach the gauges to the face plate you make so they can come foreword with the dash face by 12”. Then just one simple coil for the wires and a coil for the temperature gauges.

There used to be a company here, Vegas speedometer or something like that, which you could tell what you had and he always had a way of adapting this to that and poof! Working speedometer! Sometimes $20 and once was $150 went poof out of my wallet however. Haha.

Nowdays some of the custom dashes get kinda cool. A neighbor has an ipad that is built in. Thats his music, all his gauges including speedometer, phone over the sound system, and yes when he parks he watches movies and YouTube all while at the wheel of his rock crawling jeep. His favorite thing to do is send a text with the screenshot of the inclinometer when he stops on steep hills. Says he is going to add exterior cameras later- kinda has me thinking for my hummer.

My point is you can do it any way you choose. Time / money.
 
To be fair I think fuel quality plays a big part. I think our fuel quality is better than average because of all the trucks running to and from the North slope. I've only changed a filter a couple of times in all that driving and it was mostly because "I probably should" while I'm working on it.
I hear of people down in the lower 48 only getting 10-15k out of a filter.
 
Will L. said:
Can you show pics of the mirror holes?

To be fair on the idea of get rid of the ds4 and replace with db2:
Search Bobbie Martins book on here on conversion.
I have a hatred towards the ds4 and pmd. Having had sommany issues with the system compsred to almost nothing ever with the db2 is why.

Being able to buy a tune for the ds4 does help if you run a big non wastegated turbo like ATT over it on a db2. Imo still not worth it because the money saved currently and future on pmd, heatsink, pmd cable, any sensors,etc. is easily offset.

Trans controller is a one time thing like ecm. If you have other 6.5 rigs with ds4 then keep the old parts. Otherwise well them to pay for the controller.

I also don’t like the gauge cluster in GM. I am an old school hot rodder. I like round gauges-more the merrier. I would sell the cluster, and put in gauges and just gonfrom there. The square body dash was the pinnacle of chevy dashes imo because it looked like round gauges everywhere. If you guys see a couple gmt400 running around with metal backing (and 1 out of wood) full of round gauges, those might be my handy work. The trick is to attach the gauges to the face plate you make so they can come foreword with the dash face by 12”. Then just one simple coil for the wires and a coil for the temperature gauges.

There used to be a company here, Vegas speedometer or something like that, which you could tell what you had and he always had a way of adapting this to that and poof! Working speedometer! Sometimes $20 and once was $150 went poof out of my wallet however. Haha.

Nowdays some of the custom dashes get kinda cool. A neighbor has an ipad that is built in. Thats his music, all his gauges including speedometer, phone over the sound system, and yes when he parks he watches movies and YouTube all while at the wheel of his rock crawling jeep. His favorite thing to do is send a text with the screenshot of the inclinometer when he stops on steep hills. Says he is going to add exterior cameras later- kinda has me thinking for my hummer.

My point is you can do it any way you choose. Time / money.
Click to expand...
All they are is 3 little 5/16 bolt holes from the old mirror brakets. Ill try to get some pictures for you
 
That would work if you can find them in SS or at least HDG. Biggest issue with a carriage bolt would be all the excess sticking inside from the square shank.
 
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