Tbi conversion help

[Tonyorlo]

I am going to drop a complete 350 tbi engine into a 75 c20 with a 4 Muncie 4 speed and I have a few questions. I'll state some of the facts first.

-Engine is from a 91ish (I will verify the year) 2500 4wd auto
-Engine harness has not been cut, every plug is still intact
-flywheel and clutch are from a early sbc
-C20 Has dual gas tanks

Questions I have for now;
-The ecm for the engine was left in the cab, how do I locate the correct ecu for that engine?
-Do I need to use an ecu from a truck with a manual trans?
-What fuel pump do you recommend I run? I am on a tight budget, so for now I am going to run a single pump. Down the road I would like to install 2 in tank pumps like the factory.

 

[1987 GMC Jimmy]

I am going to drop a complete 350 tbi engine into a 75 c20 with a 4 Muncie 4 speed and I have a few questions. I'll state some of the facts first.

-Engine is from a 91ish (I will verify the year) 2500 4wd auto
-Engine harness has not been cut, every plug is still intact
-flywheel and clutch are from a early sbc
-C20 Has dual gas tanks

Questions I have for now;
-The ecm for the engine was left in the cab, how do I locate the correct ecu for that engine?
-Do I need to use an ecu from a truck with a manual trans?
-What fuel pump do you recommend I run? I am on a tight budget, so for now I am going to run a single pump. Down the road I would like to install 2 in tank pumps like the factory.

The ECM that you want is probably gonna be a 1227747. That's 87-92 trucks without an electronic transmission and with an external ESC module. Don't buy it from a parts store because it won't have a PROM. I say go to a junkyard that has square bodies and GMT400s and get you one. That or go on eBay. It's a gamble, but worst case scenario you have to buy a remanned one from the auto parts store and transfer the PROM into it. Also, make sure that it wasn't a '92-'95 truck with an internalized ESC module. It's highly unlikely since it was a manual, but I've been helping my brother work on a '93 Z71 that he bought that has a hick 4.3 to SBC swap. The TBI stuff is all mixed and matched so I'm just saying you can't be too careful. The module is on a carrier on the passenger side of the intake manifold. It has lots of pins on it. Manual versus automatic only matters on the later OBD I computers since the automatics weren't computerized until later. And they say Walbro is the best in-tank pump. Hope this helps.

 

[1987 GMC Jimmy]

It should have the ESC module since it was a manual. It's the little module with the plugin that has the cut wires.

 

[yevgenievich]

I have a 747 ecm for sale in the suburban part out thread. You might get a light because tcc will be disconnected. But overall should be relatively straight forward.

 

[Tonyorlo]

I'll have a hard time finding the specs on the truck because all I have is the engine and harness, the cab and ecu are long gone. I'm sure the harness will be differentfor an auto, it would have more connections to the trans right? I found quite a few 1227747 Ecus on eBay. So it will physically plug into my harness, and being that it's an early one it does not control the transmission. If it matters, the engine does not have a/c or a smog pump if that will effect the ecu?

I have experience with multi port efi systems like megasquirt but none with tbi. Let's say I throw a set of headers on this engine, will it cause me greif? The truck will have a dual exhaust and no cats. Will the harness have multiple O2 sensors?

Sorry for the dumb questions, I need to find some factory wiring diagrams for the 91.
Thanks for the reply!

 

[Tonyorlo]

It should have the ESC module since it was a manual. It's the little module with the plugin that has the cut wires.

The donor truck did not have a manual trans. It was auto.

 

[Tonyorlo]

I have a 747 ecm for sale in the suburban part out thread. You might get a light because tcc will be disconnected. But overall should be relatively straight forward.

Great! I'll shoot you a PM.

 

[Tonyorlo]

I ran out and took a look at it. I don't see the esc module. It does have this on the passenger valve cover, it looks like it has something to do with the egr.

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The casting # on the block is 14093638, which from all I can find it's a 87-95 block but that's not helpful.

EGR will have to stay correct? I don't not have emissions testing, but I don't want to hurt drive ability though.

 

[1987 GMC Jimmy]

Yeah, that's the EGR solenoid. I'd just keep it instead of fooling with tuning it out of the ECM. Are the two ECM plugs blue and red or not color coded? The 7747 won't work with the color coded plugs. The fact that you don't have a ESC on the outside leads me to believe it had it in the computer so the model number computer I gave before wouldn't work. You can search the number on the TBI, also, and maybe that'll give you clues. This worries me because my brother's '93 is the same way, and it has a 4L60E. The only way to get them is with the ESC on the outside and no provisions for a transmission or with the ESC on the inside and transmission control. The worst this will do is a Code 74 maybe and whatever else goes with the transmission. Plus the TCC solenoid as mentioned before. I'd hold off until you found out the year of the truck it came out of because it's not gonna do right with the aforementioned model computer if what I've stated above is the case. These aren't dumb questions, though. I don't want you to get the wrong thing.

 

[Tonyorlo]

Worst case scenario, I pull the intake and throw a carb on it. I just would love to keep the tbi for drive ability. The plugs to the computer are brown. Both the same color. (Assuming I am looking at the correct plug)

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Will I be better off leaving the exhaust manifolds on the engine? Thanks a lot for the help!

 

[1987 GMC Jimmy]

Worst case scenario, I pull the intake and throw a carb on it. I just would love to keep the tbi for drive ability. The plus to the computer are brown. Both the same color. (Assuming I am looking at the correct plug)

You must be registered for see images attach

Will I be better off leaving the manifolds on the truck? Thanks a lot for the help!

If you keep the TBI, you can do manifolds and stock one wire O2 sensor or headers with a three wire heated sensor. This looks like the plugin for the 16147060. That one is for a '91-'93 350 with a 4L80E. That means the pinout is slightly different and the internals are a bit different than the 7747 because the 7747 is a 160 baud ECM with a PROM/CALPAK and the 7060 is an 8192 baud PCM with a consolidated MEMCAL, plus the 7747 has ESC on the outside like in the picture I showed you. I'm not spouting acronyms; I'm just trying to discriminate between the two. Look over your setup for a dangling ESC sensor or a plug, but it doesn't appear to be there. The ESC provisions should definitely be inside this particular ECM, and you can program the electronic tranny stuff out of the MEMCAL if you want to do that. Also the VSS and TCC provision if you need to also. That being done it should run in closed loop with no check engine codes granted all the sensors are working. I'd like someone to come behind me and verify this because it's pretty important. Whew, this is making my head spin! Overall, it just seems like it would be easier to take the ECM with the electronic spark control in it already, going with the observation that your truck had it this way from the factory, and deprogram the MEMCAL to match your needs. That's just my thinking. I don't blame you for wanting to keep TBI. I'd be doing the same exact thing.

 

[Tonyorlo]

A few questions,
Can I change the pin out on the harness to work with s 7747 and somehow add an ecs?
Say I go with a pcm, how hard is it to find someone to burn a chip(or program) the pcm to now throw a code because of the missing trans sensors? If so, how much will that cost roughly?

I've done a few megasquirt builds, so I have a decent understanding of programs and a basic knowledge on how these systems work. Can I buy a program and cable, and re program a pcm myself?

I feel like either way, I will be better off with the tbi. As for the tank pumps, will I need to add a switch to the tank selector to kick on and off pumps depending on which tank is in service? I may just do a inline pump to simplify things until I get all the bugs worked out.

 

[Daveo91Burb]

Not sure if this would be helpful or not but I'm pretty sure I still have the ECM from my '90 parts rig. It was a '90 V2500 burb with a 350 and TH400 tranny. I probably have other TBI parts from that rig, too, if there was something else specific. If this might work let me know and I'll dig it out and post the P/N.

 

[1987 GMC Jimmy]

A few questions,
Can I change the pin out on the harness to work with s 7747 and somehow add an ecs?
Say I go with a pcm, how hard is it to find someone to burn a chip(or program) the pcm to now throw a code because of the missing trans sensors? If so, how much will that cost roughly?

I've done a few megasquirt builds, so I have a decent understanding of programs and a basic knowledge on how these systems work. Can I buy a program and cable, and re program a pcm myself?

I feel like either way, I will be better off with the tbi. As for the tank pumps, will I need to add a switch to the tank selector to kick on and off pumps depending on which tank is in service? I may just do a inline pump to simplify things until I get all the bugs worked out.

I mean, the 7747 will plug into that harness, I'm very sure. Like you said, you'll have to reconfigure all the wiring by comparing the pinouts on both. You can contact Harris Performance and try a mail order chip in the 7060. You're not getting a bunch of parameters changed to compensate for an engine build so I'd think it wouldn't be ridiculous, but it wouldn't be dirt cheap either. I'm sorry I don't have better answers. I have the 7747 in my square, and I have a primitive CCC computer in my Caprice, but I haven't gotten around to needing to tune.

 

[Tonyorlo]

I contacted Harris, and a few other chip burning shops. I explained the situation and mentioned that I will most likely need a 7060. I somewhat frequent on thirdgen.org, so I did a little digging over there. All of those guys buy a cable and burn their own chips. Which is way more than I want to get into at this moment, but maybe down the road I might get the urge to try it, especially if I decide to make some upgrades. Being that this truck will be somewhat a tow rig, I may just throw a tpi system on it in the future.

For now I'm going to wait for these guys responses and try to locate a ecu. I can go to the junkyard and try to find a 91-93 V8 truck to get the ecu. What if I find one with a manual trans? Can I just use that ecu with my current harness and then not have to burn a chip?

Thanks for all the help so far!