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I want to Convert my 1990 1500 Suburban 4x4 from gas to diesel with a Cummins.

5K views 23 replies 8 participants last post by  TimoFinn 
#1 · (Edited)
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How much for a 350 gas to Cummins conversion? And what are the difficulties?

Not to mention wanting to have decent fuel mileage compared to my 350

My Transmission is fully rebuilt 700R4 and the gear ratio is short, shifts fast.
 
#2 ·
buy a dodge !

It's a lot easier to sell it and get a dodge. A local heavy equipment mechanic converted his older ford dually a to a large CAT, Motor home rear axle, larger front axle, lots of work. BUT it will pull his big traler 70 mph up any hill, I don't know what fuel milage is.
 
#3 ·
lets start from the bottom up.
axles, well, atleast the front axle will not handle the the weight.
you will need to install a d-50+ straight axle.

transmission... useless, you will need to go dodge trans, which puts the pumpkin on the driverside. again another need for an axle swap.

you will need to drop the tank, and remove the fuel pump.

lots and lots of fabrication will be required to the chassis, and the firewall

all electrical will need to be gutted.
this means you will need to tear the dash apart.

mixing these two will be a big chore.
i would advise aginst it.

i am basing this off of the 89 F350 460 auto truck i swapped a PSD into.
the work ive done on a old 90 1500 i had, and my 15+ years experience of building bastard vehicles.
 
#5 · (Edited)
I thought it might have been a good idea to take out the gas engine and put in a diesel for fuel efficiency since I like to keep my vehicle. And since my vehicle has already been primed and sanded for paint soon along with the fact that its a 4x4.

I was thinking about either selling it now and get a early 1980s to 1990 suburban diesel 4x4(which I don't mind sticking with the 6.2 Detroit Diesel if i cant get the cummins)or just go ahead and get the paint on the one I have now , keep it for a while and then sell it for a 80s to 91 diesel suburban


My main objective is fuel efficiency, unless there is a way for that with a gas 350?
 
#10 ·
The 1990 Suburban is the 1973-87 truck architecture. I've seen this swap done on those trucks and while involved, it is not nearly as difficult as some have made it out to be in this thread. You will NEVER recoup your investment in fuel savings, so don't use that as a rationale, however.

You DON'T need to "gut the wiring". The Suburban is a TBI motor and the wiring harness for the TBI and emissions is relatively stand-alone on these trucks. There is nothing in the dash that requires the computer. The gauges all use separate, dedicated sending units. You just need to screw them into the new motor. You can get Cummins adapters to the original TH400. You will need to figure out how to operate the vacuum modulator on the trans, however. On the GM diesel trucks there was a Vacuum Modulator Valve on the injector pump linkage that essentially mimicked the manifold vacuum profile of a gasoline engine with throttle position. This VMV was used to modulate vacuum from the diesel engine vacuum pump to operate the vacuum modulator in the trans. If you go with a 700R4 (which will need to be beefed), the TV cable solves this problem.

Since these trucks were available from the factory with a diesel, you can get the diesel fuel system parts to replace the gas TBI parts. Expect to pay WAAAY more than you think to do this swap.
 
#12 ·
go price a diesel,,, add 5k for the swap and figure if you could ever recover the money? The truck will be worn out before the engine.The cost of diesel fuel is more than gas. If you need a diesel truck,buy one. Or buy one the same as yours(wrecked) and swap the parts You "can" do it. But why? Make a valid pitch to why?

6.2 diesel is a pathetic engine,about 85 use able hp
 
#15 ·
Again, you will be MUCH further ahead financially to sell this truck and buy one with a factory diesel. As for the cost of premium, that's your choice. The truck is designed to run on regular from the factory.

As for the Cummins swap, here's what one looks like in that truck:



Here's a K5 Blazer with a 4BT and turbo:



Try Google. They are all over the interweb. You would be far from the first to try it.
 
#16 ·
I've got 355k miles on my Cummins Dodge 3500. It's very reliable.

I'd suggest you sell your truck and look for a pre 99 Dodge 12 valve Cummins. These are have a mechanical injector pump and are easy to add some hp and torque. I'd look for a 5 spd manual (NV 4500) rather than an auto. Look for a southern truck out of the rust belt. Even if it has a couple hundred K on it there are still lots of trouble free miles left. A good 12 valve is hard to beat for reliability. They are relatively easy to service too. You can expect well over 20 mpg driven nicely.

One thing to keep in mind with light truck diesels is that if you can't fix it yourself they can be very expensive to have serviced. Most of us keep a card just for emergency.

As noted converting is very tedious and definitely not cost effective. A Cummins will shread a 700r4, they are hard enough on the stock trans.

Check
Dielsetruckresourse.com

DTR for short. There is a conversion thread there. It's the best board for help with Dodge and Cummins.
 
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