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1991 gmc 5.7 as a swap...?

Will L.

Will L.

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Boulder City Nv
Nephew has a 74 Jeep j10. P.o.s. AMC 360 is coming out along with trans & transfer case. He is looking at the '91 5.7 (iirc tbi that year) that his friend is selling. He wants to use GM engine /trans as replacement.

His friend who has hopped it up a bit, is 1 year out of highschool. No clue what has been done mod wise yet.

I can't remember ever using that engine as a replacement for anything. What electrical is needed and expected headaches?

Yes, you all know I tried leading towards a take out optimizer, but Southern NV dmv is not exactly fond of gasoline to diesel conversions - so not gonna happen.
 
The TBI 350 engine should be a relatively easy swap.
He will need a fuel pump that will put out about 18psi IIRC. It also will need a return pipe installed back to the fuel tank.
Also all of the wiring will need to be swapped over and the ECM installed.
Those are an OBD1 system and relatively easy to diagnose when something doesn`t seem to be functioning as it should.
 
I also am wondering what cam was installed in the engine, if it has been hopped up. The OBD1 system does not like a lumpy camshaft.
 
3500GMC said:
Trans could use a shot in the arm, TH700R4 probably. Good lil gearbox IMO, lots of upgrades for these.
Click to expand...
YUP, that would be the box.
Biggest thing is to keep the throttle valve cable properly adjusted. Bad things happen if it gets out of adjustment and it will burn up the transmission.
As 3500GMC suggested, there are a lot of real nice internal up grades for this transmission that`ll allow it to be put behind even the most souped up streetable engines without any problems.
 
Ok cool.
What about speedometer? I rember almost nothing about that.
He wont care about what type of gauges I'm sure, but would you guys think it's better off doing a major dash modification to fit the 91 dash, or if speedometer is easily rectified, then we can do all mechanical gauges.

I am going to try to talk to current owner about exact mods done, no clue on cam yet. Kid that owns '91 now is nuke school bound in the Navy, won all kinds of robotics competitions, and all the kids (2500 ish)from their highschool held him as top wrench spinner. So I doubt he did any hackery. My nephew did just mention the guy said "something made a noise, haven't look at that yet". He is selling because of Naval commitment and when done will just need a rice burner- hot rod pickup days are done for him. (He thinks- haha, we all know it's a life long addiction).

Personally I always hated the tbi system. Avoided them when possible, but am trying to not let my personal taste skew a good option. If this is a can of worms, or other issues besides what is pointed out so far, please speak up. I Promise you wont hurt my feelings.

I would be more inclined to drop on a carburetor and go 1980's style, but dont know what else is needed for that era of small block. I rode 1960-70's until hitting the 6.2 diesel, avoiding computer controlled stuff as much as possible.

My nephew is doing this on a shoe string budget. As in had to take a job 3 miles from his home so he can walk to and from work because of no transportation. After buying the truck he will have about $300, so I am going to convince him to just drive the truck as is so any problems pop up before the retrofit. Also he is planning on my garage for the work, which is in line behind my hummer that I hope to start on mid September and expect 2-3 months to finish. So at least he has a rig for a few months that way. And can save up more $.

Anything special for this tbi, trans, Xfercase (just hit me- hope it's a 4wd) I should look for in the prepurchase inspection?
 
The TBI is a very good and dependable system. Not much goes wrong with them, when it does it is usually pretty simple. My 93, that I sold, it would get 17mpg on a bad day.
dont be afraid of the system, they are really quite simple, diagnosing problems is relatively simple too.
If it has 4X4, be sure that the T~Case functions as it should and that the trans shifts firmly without slipping.
It is good that He will be driving it for a while before the retrofit, He can then get more familiar with the ssystems.
If the fuel pump ever needs to be replaced, it is easier to lift the box, then every thing can get cleaned and warshed before breaking any connections.
There are adapter that can be bought, I`ll look and find the website that has some real good ones. They have the drive gear setup and the signal generator all in one unit. I think at the time I was looking at them that they were around 75 bucks.
 
So we were about to go look at it, and when his friend found out his plans he said no. The noise was something in the engine going bang in a bad way and the price is based on the rest of the truck. Wouldn't sell it to him because he new the engine will need a complete rebuild. He could have stuck him with it for the $, but integrity is alive and well.

Good to know about the tbi in case that's what he ends up with. His search continues...
 
Will L. said:
So we were about to go look at it, and when his friend found out his plans he said no. The noise was something in the engine going bang in a bad way and the price is based on the rest of the truck. Wouldn't sell it to him because he new the engine will need a complete rebuild. He could have stuck him with it for the $, but integrity is alive and well.

Good to know about the tbi in case that's what he ends up with. His search continues...
Click to expand...
Too bad You are not a little closer. I have a K1500, 350 but a manual trans that I would let go for $800.00 or maybe even a little bit less. It too needs the engine rebuilt. I have the engine all apart and loaded into the cab. I had spent over $600.00 on the truck, to discover that a noise like a ticking lifter does not necessarily mean that it is a lifter. Turns out that the no.7 rod bearing took a spin around the rod, maybe even a few. Bearing was barely galled. I did install a new cam, lifters, TC and sprocket set, rocker arms, push rods and oil pump. Also went through the brakes and a couple of new ball joints, doesn`t have but about five miles on any of it. Soon as the engine warmed up and the tick was still there, it was parked. I then pulled the engine and tore it down. Just dont want to dump anymore money into a truck that I dont have a use for.
 
Tbi engines can run really well, but you have to know what you're doing with the heads(most go hog wild thinking the swirl must go, and ruin them), and be CONSERVATIVE with the camshaft. Last one I built dyno'd a bit over 240 at the wheels, and that was with a junk 700r4 trans with no lockup. The tbi system is DEAD simple, and I think that is what deters most from them. Otherwise they are SUPER easy to carb swap. But to make the tbi work is very easy to do. Small blocks only need 12-13 psi of pressure(94-95 454's were the odd balls at 32-40) to work. It's a bare bones system with a tps, cts, map, O2(most were 1 wire, but the 3 wire upgrade is worth it's weight in gold), speed sensor(depends on year and what body as to the type of signal and pulse per mile), and the 8 pin hei distributor. Most issues with them are either a bad/failing ignition module not switching from internal to ecm timing control, not amplifying the magnetic pickup signal properly to a square wave signal for the ecm to read(happens often with aftermarket modules), or the pickup coil gets weak or cracks and puts out low voltage or a double signal. Starting in 91 2500+ could have the 4l80e trans(remember 91-93 4l8pe trannies are "unique"), or in 93 the 4l60(700r4) went away and the 4l60e came out(95 is a 1 year only and 1st gen pwm tcc control). The ecm's used are not water proof in any way, and must be mounted inside the vehicle. Tuning is not difficult, but early ecm's require replacing the chip socket and running an adapter while later ecm's can accept modern chip blanks(91 with 4l80e or 93 with 4l60÷ and up have the modern controllers). Converting to stand alone is fairly straight forward and simple with them, and is by far the easiest one to do, hence why so many people use them on other engines to convert to fuel injection(howell tbi system's is all GM parts off the shelf put together in a diy kit).

Don't expect big HP, but you can get some SERIOUS stump pulling torque out of them that comes in just off idle that will make you question wether it's a diesel or not. Upgrades are plentifull AND CHEAP, as well as tuning is easily achievable if you so desire.
 
What's wrong with the existing AMC 360? Why not patch it up with aftermarket ignition etc. and go with it? Save a bunch of time money and effort.
 
My brother in law, who was normally a good mechanic, did a rush hack job on rering& bearing and screwed it up good. To do it right because of his hackery..
New crank, line bore, cam, distributor, oil pump, and on and on. Just not worth it.
It is a "salvageable " engine for rebuild, but it need to be a Jeep fan with some extra change in his pockets.

The trans is ok, but the xfer case is a known p.o.s.- not his specifically, but that model in general.

The truck really belongs in the hands of a collector that can save it all correctly, but he is your standard broke kid trying to help his mom put food on the table since his dad is a jackwagon that wont pay child support or any of that stuff.

It's all good- character building for him to struggle through.
He will find a good donor somewhere...
 
:p Sell it and start with something that doesn't need major work and expense to get on the road. Even a swap a different 6.2/6.5 engine in one of our rigs is not as expensive as a swap to something else. Being broke and attempting to do this IMO is a bad idea from the word go. The little krap adds up quick on a conversion and generally when you are in the middle of it and need a $500 custom drive shaft.

Start with blown engine pickup or burb for less than $1100, add $2000 for a take out 6.2 with misc parts to drop it in and there you go for a 4x4.
 
That's kinda why I was hoping that one would have worked out. Then maybe he would just stayed in the gmc and been happy with it and sold the J10. Unfortunately the kid has had so much pulled out from under him he is holding onto that thing for dear life. Lead a horse to water....

Not like I did everything the smart way either. If I always did It would start with selling my hummer. haha Yea like that'll happen. Stupid is as stupid does. Maybe my stupid is contagious?
 
So teach him how to properly rebuild a AMC 360 then... If THAT doesn't change his mind. Seriously that would be the better road to take esp. from an education learning for the future angle. This way he can repair his own rides in the future. A Frankenstein conversion may turn him off to that as it never fing runs let along gets finished.

A used 360 engine in ruining condition may be available.

I assume this 360 is like a knock or otherwise not smart to push any further?

Let him blow the transfer case. It's not like rub-through or shift yoke wear doesn't kill ours.
 
It is a gonner. I taught him how to put in the new bearings and plastigauge (after his dad did new ones less than 100 miles ago) and there is no running this engine without $2,500 minumum. The crank and mismatched rods are so far out of spec that I bought all 4 sized bearings to try to imitate select fit, and it still can't hit specs.

Needs new cam and distributor& oilpump even though he just put those in new. The oilpump was replaced but not gap adjusted like the crap design requires and it took out all 3. I think it bounced some valves against the pistons as well. Too much $ and time to be worth it. Because when running-Then it is still a p.o.s.

Only good to the hard core collectors. AMC screwed the pooch on this design. If his mom didnt need to sell the oshkosh pusher rv with the 12v cummins in it... he wanted to put that in there and registered it in Az to avoid DMV no sense about gas to diesel conversion. Heck, that cummins is so new, I thought about it for the Hummer haha.
Hopefully he can just find a gm truck for a grand somewhere and go from there.
 
There are GM trucks out there for reasonable prices. might need a transmission or who knows. get on craigslist and look around. There must be something out there.
 
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