1987 V10 with 1974 engine- need TBI Help

[gmbellew]

hope th

I researched the IAC reset procedure and tried it multiple times as described above. It seems to idle fine and I can adjust it with the IAC disconnected (with the new TBI). When the IAC is connected back up is when the idle goes crazy. It starts out idling really low almost stalling, then goes really high a minute later. All connections are good or new. I have ordered and replaced many of the connectors. And the fast idle does not work with the new TBI when cold.

What really baffles me is how different the two TBI's are from each other and how the truck runs. The old TBI it runs better overall and has a good fast idle when cold but the idle hunts up and down when hot no matter what. And it won't idle at all when I try the IAC reset procedure. The new one the idle is so erratic with the IAC connected and mostly idles at 1800 RPM. I can't adjust it down. And the fast idle does not work at all.

I unfortunately reached the end of figuring it out. It's at a local shop now. The guy is very knowledgeable with TBI's and older systems. Worst case if he can't figure it out he said he can convert it to carburetor. About 1500. It will probably be there a month as things there take time and he has a lot of trucks he's working on. I'll report back what he finds outs so that if anyone else runs into this issue they will get an easier and faster solution.

hope they get it figured out. sounds like that new TB might have some sort of other issue. hope you also gave them the old one to help trouble shoot.

 

[bucket]

If you can get it to run fine without the IAC connected, by adjusting the base idle screw, that is an option for driving it as well. Is it right? No. But is it better than a carb swap? Most would say yes. It's certainly cheaper.

 

[JT58]

If you can get it to run fine without the IAC connected, by adjusting the base idle screw, that is an option for driving it as well. Is it right? No. But is it better than a carb swap? Most would say yes. It's certainly cheaper.

HMM I didn't know that was even an option and if it would even run right.

 

[JT58]

hope th

hope they get it figured out. sounds like that new TB might have some sort of other issue. hope you also gave them the old one to help trouble shoot.

Yes I gave the shop both TBI's and told them the story.

Not to brag but I am usually pretty good at figuring out things even when shops can't. Has happened to me a few times where I had to fix a shop mistake. This one has me really stumped and has me wondering if the shop can even figure it out. I'm almost expecting them to tell me they need to do a carb swap. Then it's decision time- carb swap or put the old TBI on so it at least runs and cut my losses.

 

[YakkoWarner]

Yes I gave the shop both TBI's and told them the story.

Not to brag but I am usually pretty good at figuring out things even when shops can't. Has happened to me a few times where I had to fix a shop mistake. This one has me really stumped and has me wondering if the shop can even figure it out. I'm almost expecting them to tell me they need to do a carb swap. Then it's decision time- carb swap or put the old TBI on so it at least runs and cut my losses.

I understand the feeling - I often tell myself that the next major malfunction I have will be carb swapping time (what has stopped me previously was the fuel pressure mismatch). I don't dislike the TBI system in any way but it is very fragile and not at all fault tolerant.

I was going to suggest checking the TPS calibration but since you have the pros looking at it now, I'll be curious to know what you find.

 

[JT58]

The shop is as I suspected extremely busy and won't get to it for a week or two. I had to buy a truck cover for it to protect the paint in the super hot FL sun while it waits its turn. (So difficult to get vehicle work done around this area, that's one of the reasons I try and do all of my own work).

The owner suggested either a carb swap or sniper fuel injection worst case scenario. I would need a new manifold, distributor, fuel pressure regulator or fuel pump to increase pressure with the sniper.

If I have to go this route any suggestions which would be the better system and be more compatible with the 1974 engine and rest of the 87 electronics? I'm leaning on carburetor.

 

[gmbellew]

The shop is as I suspected extremely busy and won't get to it for a week or two. I had to buy a truck cover for it to protect the paint in the super hot FL sun while it waits its turn. (So difficult to get vehicle work done around this area, that's one of the reasons I try and do all of my own work).

The owner suggested either a carb swap or sniper fuel injection worst case scenario. I would need a new manifold, distributor, fuel pressure regulator or fuel pump to increase pressure with the sniper.

If I have to go this route any suggestions which would be the better system and be more compatible with the 1974 engine and rest of the 87 electronics? I'm leaning on carburetor.

I would do neither of those. If the worst symptom is a hunting idle, I’d just drive it until something bigger breaks. But I’d exhaust all the other things mentioned first, including getting a cable and a way to see what the ECM is doing. Cable and software, even if you had to buy a computer, is going to be cheaper than either of their options. I’d put the old TBI back on as it was, go over everything with a fine tooth comb mentioned in this thread, and then scan and see what the ECM is up to. And if I wasn’t happy after that, I’d regrettably do an LS swap before either of the other two options.

 

[JT58]

I would do neither of those. If the worst symptom is a hunting idle, I’d just drive it until something bigger breaks. But I’d exhaust all the other things mentioned first, including getting a cable and a way to see what the ECM is doing. Cable and software, even if you had to buy a computer, is going to be cheaper than either of their options. I’d put the old TBI back on as it was, go over everything with a fine tooth comb mentioned in this thread, and then scan and see what the ECM is up to. And if I wasn’t happy after that, I’d regrettably do an LS swap before either of the other two options.

Hmm I had not through of an LS swap. Do you mean the 4.8 or 5.3 engine? My wife has a 2013 Silverado 2WD short box in superb condition. With the 4.8 it moves and sounds real good with MBRB CAT back duals. Are adapters made to mate up with the manual tranny to do this kind of swap? I'd probably have to invest 15- 20K to have a shop around here do that kind of swap unless I transported it up north somewhere where prices for vehicle work are more reasonable.

I like your idea of putting the old TBI on and let the idle hunt- at least it ran. I could try to sell it that way- the truck has very decent body and frame, no rust. I told the shop if someone liked it I would sell it for 30K. I have near 50K invested and a book of receipts and work done. I paid 23K for it, engine and chassis caked in oi, everything leaking oil profusely. Might be a good BAT truck but I bet it will sell of 20-23K.

 

[Sgt Gus]

What did you spend 25k on, interior and paint?

 

[JT58]

What did you spend 25k on, interior and paint?

Well it's a HUGE list- I have a book of the work and receipts. And some of it my work, some a shop and their labor. For starters- dual fuel tanks not working- needed all new wiring and new wiring harness under the truck, fuel pumps, all new wiring under the truck to get the turn signals and brake lights working, new front and rear brakes, drums, emergency brake cable, bed and tail gate sanded, primered and bed coating applied, all new U Joints, new oil pan and gasket, new clutch and flywheel, new clutch slave cylinder (2X), complete undercarriage cleaned and degreased- axles, drives shafts, body panels, etc. sanded to bare metal, primered and painted, front wheel well liners removed, repaired, sanded to bare metal and painted, front end grill area disassembled, sanded and painted, new front fascia, new battery (2X), new radiator, thermostat, valve covers and gaskets, new air cleaner assembly, power steering pump, power steering gear box, all new tie rods and ends, rear differential cover, all fluids changed and flushed, instrument panel bezel cleaned, repainted, gages, dual shock truck- added the second shock, all new shocks, new spring bushings, front wheel bearings and seals new. Interior work, floors, paint, bench seat. There is much more. Paint was good driver quality when I bought it so no repaint.

 

[JT58]

Update on this thread and my final report. The shop found an issue with the new TBI- said it was an incorrect TBI for the truck. It looked exactly the same to me. So he took the original TBI and rebuilt it using the components from the new TBI. It runs pretty good now, idle is not perfect, it hunts just a bit maybe 100 RPM or so- way better than it was previously and it at least idles and drives favorably. So now is great time to part ways with it. I have too much invested and time to cut my losses. Will try to get 25K for it- about what I paid for it 4 years ago in really bad shape, leaking profusely and needing so much work. It's a good platform for someone to take it to the next level.

 

[Olegmbuilder]

I did not want to post another TBI thread but I need help. I have read just about every TBI post on line. I have a beautiful 1987 V10 short bed stock, 350 engine, SM 465 manual. (Engine is a 1974 transplant) with original 1987 electronics. It runs great, powerful and steady at all RPM except it does not idle steady- when warmed up. It hunts up and down. It's fast idle at start up is perfect and steady. I've tried just about everything for 3 years now- new EGR, TPS, IAC, MAP Sensor, Plugs, Wires. Also new charcoal canister, two new fuel pumps in the tanks, all new vacuum lines. I used top notch parts too- AC Delco when available. I tried resetting the idle but it appears and that OBD2 port is inoperable or dead. Truck has no lights- check engine, etc. When I jump the ports and disconnect the IAC the idle screams high. I have checked for vacuum leaks- none. The truck had a bad thermostat, stuck at 160- I put in a 180 Degree, did not help. The TBI electronics supposedly need 195 degree although this may be too hot for the 1974 engine.

Suggestions to fix it? Could the fuel pump pressure be too low- inadequate fuel pumps in the tanks? Maybe the thermostat needs to be 195 degree? How to fix inoperable ODB2? Is it worth the aggravation?

Or should I just go carburetor since I do have a 1974 engine? I'd have to change the intake manifold (The engine already has the 1974 heads with side bolts, not the center bolts- someone before me changed to 87 TBI manifold), change to HEI distributor, 4 barrel carburetor and install a fuel pump regulator. I am going to have a local shop assess it in a couple of weeks although they charge $$$$$ and may not be able to even do anything since it is a mix of 1987 and 1974.

The rest of the truck is so great, mostly all of my own work to restore it so far. It drives, tracks and runs like a new truck except it won't idle. I want to do what is best and most economical. Thanks for any help.

Find a 74 carb or a few years newer. Sometimes old don't mesh with new parts.