Now we move into desperation territory (seeking advice)...

[gmbellew]

1989 1990 1991 1992 Chevy GMC Truck Engine Computer ECM 1228747 5.7L 7.4L | eBay

This ECM will fit any application that originally used the 1228747 ECM. GM installed this 1228747 ECM in a variety of GM applications. This was possible because each model received their specific PROM (also known as chip) from the factory.

www.ebay.com

you will just have to swap your PROM to the new ECM.

 

[gmbellew]

Fuel pump relay has been replaced. I swapped it as an outside chance it could be causing an excess electrical draw/voltage sag. I'm not losing the fuel pump itself (I even jumpered the oil pressure switch to force an always-on state and still had it shut down).

When it went into the second failure mode of spitting back through the air cleaner at any amount of throttle, it again cleared itself after a power cycle.

I was thinking to ONLY power cycle the fuel pump instead of cycling the key. Just trying to narrow it down. link to new ECM above. that's the same vendor I got my spare ECM from when I thought maybe my ECM was bad.

 

[YakkoWarner]

I don't know any more than what I read on their website from doing some research. But if you just want to see what the ECM sees at the sensors, how it is adjusting fuel, RPM, etc, I've been pretty darn pleased with ALDLDroid app on my phone and a Bluetooth ALDL cable from 1320 electronics.

Havn't been able to get back to this for a bit - life intervenes.....

How do I find these 1320 electronics people? They don't seem to have a web site, their YouTube channel has 5 videos posted a decade ago and no contact info. I think its pretty clear I need this kind of tool if I want to try to save the TBI system rather than carb swap, but all appearances indicate they have been intentionally removed from circulation. If they DO still exist, I'd love to know how to buy this...

 

[YakkoWarner]

1989 1990 1991 1992 Chevy GMC Truck Engine Computer ECM 1228747 5.7L 7.4L | eBay

This ECM will fit any application that originally used the 1228747 ECM. GM installed this 1228747 ECM in a variety of GM applications. This was possible because each model received their specific PROM (also known as chip) from the factory.

www.ebay.com

you will just have to swap your PROM to the new ECM.

I wonder if we just discovered the problem: That link is for an 1228747 unit, my truck seems to have (upon visual inspection) a 1227747 unit. Did someone swap in the wrong ECU??? Is there any way to determine which ECU I am supposed to have?

 

[gmbellew]

I wonder if we just discovered the problem: That link is for an 1228747 unit, my truck seems to have (upon visual inspection) a 1227747 unit. Did someone swap in the wrong ECU??? Is there any way to determine which ECU I am supposed to have?

There might be a sticker under the dash by the ECM that has the number in case somebody installed the wrong one? But I'd think you'd have larger drivability issues with the wrong computer.

Could also be that they swapped ECM with the new body style and those got a different computer. Might have to research to see which is correct

 

[borderburb]

I had a similar acting '86 K10 years ago that I checked every relay, fuse, switch and ground but couldn't find anything wrong.

I ended up taking it to a shop. They found a loose connection in the fuse block on the firewall. After fixing that it ran like a champ again.

 

[1lejohn]

I might switch out the plug in Prom. I would think that its corrupted. It's what really tells all the circuits when to switch, the injectors to fire, spark ETC. The ECM is a solid-state device if something failed in it, I don't think a power reset would fix it. It would stay broken. Example bad solder joint, failed triac, diode, solid state relay. JMHOP.

 

[Hunter79764]

2 thoughts, first is I had a similar issue on a different setup, tracking things down seemed to narrow it down but threw me for a loop continually. Ended up being a ground terminal on a bolt that I didn't tighten (stupid mistake, "I'll get it later" then went to bed and forgot...), bouncing along the teeth when the throttle opened and wiggled a harness. Not saying that's your issue, but remember that if you find yourself beating your head against a wall for too long, you might be on the wrong wall.

Second thought, if you aren't big on an Ebay ECM and feel like a project, look at Microsquirt or Megasquirt, they are DIY style ECM's that have a ton of support for GM TBI systems. It's not the cheapest (factory ECM should be cheapest, someone familiar with the OBD stuff can confirm but I think that you should have a range of ECM's and/or PROM's that would work, even if it had to be a 1989 454 those should be common enough), but it would be less than an aftermarket EFI, probably less than a proper carb swap although I haven't dug into everything on that yet. And x2, if you go that route, run an adjustable regulator to knock the psi down to 3-5 or whatever and you'll be fine.

How to MegaSquirt Your TPI or TBI Chevy Small-Block V8 or V6

How to convert to Fuel Injection on SBC V8s with TPI or TBI injection and HEI ignition with electronic spark timing - MegaSquirt EFI

www.diyautotune.com

ok, last thought... LS swap?


Sorry, had to...

 

[YakkoWarner]

2 thoughts, first is I had a similar issue on a different setup, tracking things down seemed to narrow it down but threw me for a loop continually. Ended up being a ground terminal on a bolt that I didn't tighten (stupid mistake, "I'll get it later" then went to bed and forgot...), bouncing along the teeth when the throttle opened and wiggled a harness. Not saying that's your issue, but remember that if you find yourself beating your head against a wall for too long, you might be on the wrong wall.

Second thought, if you aren't big on an Ebay ECM and feel like a project, look at Microsquirt or Megasquirt, they are DIY style ECM's that have a ton of support for GM TBI systems. It's not the cheapest (factory ECM should be cheapest, someone familiar with the OBD stuff can confirm but I think that you should have a range of ECM's and/or PROM's that would work, even if it had to be a 1989 454 those should be common enough), but it would be less than an aftermarket EFI, probably less than a proper carb swap although I haven't dug into everything on that yet. And x2, if you go that route, run an adjustable regulator to knock the psi down to 3-5 or whatever and you'll be fine.

How to MegaSquirt Your TPI or TBI Chevy Small-Block V8 or V6

How to convert to Fuel Injection on SBC V8s with TPI or TBI injection and HEI ignition with electronic spark timing - MegaSquirt EFI

www.diyautotune.com

ok, last thought... LS swap?


Sorry, had to...

MegaSquirt looks like quite a neat solution - only problem is I'm not sure who I could hire to assemble the thing since it apparently comes as a bare PC board and a million loose components (some assembly required, batteries not included, not suitable for children under 12 without adult supervision, etc....). If this could be sold as a already assembled unit ready to plug in and go, I'd really be considering it. I'm pretty good at doing basic electrical stuff but building a computer one capacitor and resistor at a time would be a bit outside my skill level.

I have someone who has ebay ordering me an ECU - we'll see if it really works or not.

The more I deal with this the more I like the idea of a carb swap - I like things that at least obey the laws of physics even if tempermentally. Doing the same thing over and over while expecting different results is insanity - doing the same thing over and over and GETTING different results is computer science. I have seen pictures of these external pressure regulators, but never actually seen one on the shelf anywhere to buy. The would make a carb swap more viable to me (not having to change the fuel pump again at least).

If I was considering repowering completely, an LS swap might make sense but that just adds even more tempermental electronics to the mix. At this point something involving boilers and steam power is actually more appealing than electronic anything.

 

[Hunter79764]

You can buy the megasquirt assembled, you will probably still need to do some harness work on your own though. Do what you think best, but the TBI computer and the LS computers are both usually pretty reliable units. Newer stuff will tell you what is wrong with reasonable degree of accuracy and run things pretty well, and occasionally has a head scratcher that's usually a loose wire or a corroded ground, sometimes worse, but it seems like a small price to pay. Older stuff (carbs) are usually mis tuned but remain fairly drivable, but more prone to mechanical issues and ethanol corrosion etc., so basically take your pick of which problems you want to solve.

 

[YakkoWarner]

You can buy the megasquirt assembled, you will probably still need to do some harness work on your own though. Do what you think best, but the TBI computer and the LS computers are both usually pretty reliable units. Newer stuff will tell you what is wrong with reasonable degree of accuracy and run things pretty well, and occasionally has a head scratcher that's usually a loose wire or a corroded ground, sometimes worse, but it seems like a small price to pay. Older stuff (carbs) are usually mis tuned but remain fairly drivable, but more prone to mechanical issues and ethanol corrosion etc., so basically take your pick of which problems you want to solve.

Well I just got my claims-to-be-remanufactured ECM about 3 hours ago, I'm certainly going to try this first and see if it solves my issues because it would be the most seamless method. If not then we go deeper down the rabbit hole (and deeper in the hole money-wise as well).

An assembled MegaSquirt would certainly be on the things to consder list - do you know if it has any kind of real-time monitoring capability like OBD-II offers? Supposedly there was a cable-interface type device that could sort-of give you monitoring on OBD-1 but it was made by a company that seems to have gone out of business about a decade ago. Harness work seems less complex than building a computer from discrete components, so I wouldn't rule that out.

I even considered a Holley Sniper-type replacement system because I know its computer can at least give you some useful info, but changing to a 60PSI fuel system is intimidating. Because of that I'm not really chomping at the bit to go that route.

Carb swap is also a drastic undertaking, but since I passed desperation 2 stops back, even drastic may not be adequate.

 

[Hunter79764]

I wouldn't recommend a holley system for what you're looking for personally, no real reason other than my feelings and opinions, but the 60 psi system isn't a problem, just search the LS threads. Hopefully your ECM fixes it, or you find another solution somewhere. I have seen stray grounds do some weird things.

 

[YakkoWarner]

I wouldn't recommend a holley system for what you're looking for personally, no real reason other than my feelings and opinions, but the 60 psi system isn't a problem, just search the LS threads. Hopefully your ECM fixes it, or you find another solution somewhere. I have seen stray grounds do some weird things.

The Holley isn't really my first choice either - it seems more targeted to the performance upgrade demographic which isn't where I'm looking to go. Its only real appeal to me is the ability to do realtime monitoring which makes troubleshooting more scientific than the limited error code info OBD1 can actually provide.

I pulled the old ECU last night - didn't see any obvious signs of problems in terms of connectors or odd burned-electronic scents. Swapping the ROM chips over was a bit tense because those can't be replaced if damaged, but I think they transplanted safely. I may pop the new unit in tonight or wait until tomorrow evening when its not sun-surface temperatures outside. Its a 50-50 dice roll on whether this will really the problem or not but the only way to know is to try it and see.