Should i fix the TBI or go to carb? And what's this wire?

[Redfish]

It just seems to me that if it is the ECM, that would be an easier and cheaper fix than modifying the fuel system. I feel like you have the skill set, the tools and the tenacity to get that thing running like it was designed.

I was determined that if I could find a TBI 350 I would make it run like it was supposed to and not go back to a carburetor. I have been able to do that and I am pretty sure you are a LOT more capable than I am. If I can do it, I just feel like you can as well.

 

[WFO]

The bypass regulator is fuel feed in from your old fuel line. Out to carburetor. Bypass line to your existing return. Does anybody know if a brass ball valve from the hardware store is fuel proof.?The way we used to do the bypass,was with a tee fitting. The straight though path is your in and out. The dogleg part of the tee is return and we used to make a brass restrictor for the return line to get the pressure we needed. I'm thinking a person could use a ball valve as the restrictor instead of a drilled piece of brass as a restrictor. We did this 40 years ago before all these cool parts were cheap and readily available.

You can get inline brass fuel petcocks from various websites.

 

[AyWoSch Motors]

Those little clickity clackity pumps don't normally need a regulator. However, the new pump you installed in the tank does. As long as it's not a bargain basement pump you installed, it should be much more reliable than the cheap inline pump. Also, I'm not sure how well that little pump can pull fuel through an inop in-tank pump.

The pump that was in in the truck is junk now. Don't no why. Its brand new, wont work.
Although i could get a new one. But how would i wire it in?
Trace down the factory wiring, or just hot wire it with a switch?

 

[Ricko1966]

You can get inline brass fuel petcocks from various websites.

If I were going to mail order something I d order a good regulator. We did what we did because it was what we had to work with.

 

[WFO]

If I were going to mail order something I d order a good regulator. We did what we did because it was what we had to work with.

You're the one that asked if a brass ball valve is fuel proof. Since I wouldn't use a ball valve intended for water for fuel, I figured I would throw out an option that was built for fuel.

 

[TFerguson]

Those ECM's are all plug and play no programing needed like with the newer cars. Prob take you 15 minutes to swap it out and cost $100 - $150.

I was gonna say the same thing. I was diagnosing what ended up being a mechanical issue w/ my 350 TBI, and bought a reconditioned ECM/PROM on evilbay for around $150. The ECM ended up not being my issue (was a flat cam lobe), but I did confirm it worked fine, so now I have a spare in case the current one croaks. Unfortunately these systems are OBD I, and so there are very limited options for troubleshooting, compared to OBD II. However if you have a check engine light on and a paper clip handy, you can get a surprising amount of clues to point in the right direction.

That being said, I may eventually go to a carb setup on mine. The only reason I would switch is to take advantage of a sportier cam/head setup. I've never tried it on a TBI system, but from what I've read it can be a real bear to get them to work with performance cams & heads, but as we well know, not such an issue with a carb setup.

Best of luck - hope you get it figured out either way.

 

[Ricko1966]

You're the one that asked if a brass ball valve is fuel proof. Since I wouldn't use a ball valve intended for water for fuel, I figured I would throw out an option that was built for fuel.

Cool,didn't mean to step on your toes,I was just clarifying that if I had the choice I'd use a purpose built regulator. Kinda like building a stroker, we used to have to find a 400 crank and rods and turn it for 350 mains,or offset grind a large journal crank for small journal rods. Now I'd just order purpose built stuff,if I had to order something. Amazing what's available today and how cheap it is.Like you can be good heads cheaper than you can build them etc.

 

[gmbellew]

I was gonna say the same thing. I was diagnosing what ended up being a mechanical issue w/ my 350 TBI, and bought a reconditioned ECM/PROM on evilbay for around $150. The ECM ended up not being my issue (was a flat cam lobe), but I did confirm it worked fine, so now I have a spare in case the current one croaks. Unfortunately these systems are OBD I, and so there are very limited options for troubleshooting, compared to OBD II. However if you have a check engine light on and a paper clip handy, you can get a surprising amount of clues to point in the right direction.

That being said, I may eventually go to a carb setup on mine. The only reason I would switch is to take advantage of a sportier cam/head setup. I've never tried it on a TBI system, but from what I've read it can be a real bear to get them to work with performance cams & heads, but as we well know, not such an issue with a carb setup.

Best of luck - hope you get it figured out either way.

I've had a similar issue that was a bad cam and also a really loose timing chain. OBD1 is great for diagnosing a lot of issues. the biggest issue is the refresh rate is pretty slow for some diagnosis (like the vacuum fluctuations that occur with valvetrain issues). so there is still a mix of old school mechanic troubleshooting needed. it's not all computers like modern stuff, but I'd still take it over a carb.

you can get more aggressive with the cam on TBI, but you need a custom chip burner or burn it yourself.

but I think with a mild roller cam swap and the right heads, you can get another 50-75 hp and keep the stock tune.

 

[wanderinthru]

Had a 87 c 10, the black one you got the tail lights from, remember. It acted the same way, you may remember all the ground wires I had added to it. It's problem ended up being a bad wire at a plug at the coil, in all that mess somewhere. Way I understand it all the firing buisness tells the tbi to shoot gas, so it can run being bottle fed, making it seem it's a fuel not fire problem. Though the issue is in the ignition system, ?, ain't computers nice. I was ready to change the computer till my old mechanic buddy (been a mechanic since th 70's said those computers don't go out). After hearing all this debate seems they do? I'm thinking climate, or moisture to be more precise. Personally I would fix the TBI, not being able to run a manual pump, seems with todays gas and parts the pump is the weak spot of tbi.

Edit to add. seems there is a plug goes into the coil, maybe, dont remember but in that area that the air breather all but rubs on the wires kink pretty tight. Mine the bottom/ inside of that kink the insulation was broke and allowing those angry pixies to jump around and intermingle.

 

[AuroraGirl]

It just seems to me that if it is the ECM, that would be an easier and cheaper fix than modifying the fuel system. I feel like you have the skill set, the tools and the tenacity to get that thing running like it was designed.

I was determined that if I could find a TBI 350 I would make it run like it was supposed to and not go back to a carburetor. I have been able to do that and I am pretty sure you are a LOT more capable than I am. If I can do it, I just feel like you can as well.

I concur on this as well. If the wiring is not batshit rigged with wire nuts and half decayed and cracked , so, decently intact, I think fixing the system as its meant to work is the best overall route. The thing about the PCMs is yeah, they had failed a lot, but they are also 100 or less brand new and a PROM chip , if inserted safely and not zapped or anything, is unlikely to be faulty, and that is about 5 minutes to make a blank new (refurb) PCM now be the proper one for the truck.
A 1995 buick park avenue ran, albeit poorly, with a PROM for a 1995 C3500 with a detroit diesel , if it means anything about troubleshooting. IE, as long as its good prom and good PCM, the engine should run. run well is different questions that can wait if he got that far.

 

[AuroraGirl]

Had a 87 c 10, the black one you got the tail lights from, remember. It acted the same way, you may remember all the ground wires I had added to it. It's problem ended up being a bad wire at a plug at the coil, in all that mess somewhere. Way I understand it all the firing buisness tells the tbi to shoot gas, so it can run being bottle fed, making it seem it's a fuel not fire problem. Though the issue is in the ignition system, ?, ain't computers nice. I was ready to change the computer till my old mechanic buddy (been a mechanic since th 70's said those computers don't go out). After hearing all this debate seems they do? I'm thinking climate, or moisture to be more precise. Personally I would fix the TBI, not being able to run a manual pump, seems with todays gas and parts the pump is the weak spot of tbi.

Edit to add. seems there is a plug goes into the coil, maybe, dont remember but in that area that the air breather all but rubs on the wires kink pretty tight. Mine the bottom/ inside of that kink the insulation was broke and allowing those angry pixies to jump around and intermingle.

The original PCMs , same with Ford at the time, had issues with solder joints and capacitors especially with vibration over time (makes sense)
They also were very very sensitive to damage at the time of service because placing the chip from the PCM in the vehicle into the new one, people used a lot of force or would not use force in the right spots, and this could doom that PCM to a short life span even if it didnt present right away.
Then GM used a poor point to use for the reference ground for the PCM for a few years (Thermostat housing or next to it) which caused issues when the other grounds got to be corroded lose or over-taxed.
The PCMs also were easily damaged because of early diagnostic steps where GM had you "Tap" the case of the PCM, but they did not emphasize how light the taps should be. So techs pounded a lot of PCMs into early graves with their hands lol.

Then, overall, the earliest of PCMs had less reliable construction than the 90+ vehicles. Early computer era, its understandable.

Also early computer trucks with EST or perhaps just that new style of distributor also was problematic till it was ironed out.

 

[AuroraGirl]

Had a 87 c 10, the black one you got the tail lights from, remember. It acted the same way, you may remember all the ground wires I had added to it. It's problem ended up being a bad wire at a plug at the coil, in all that mess somewhere. Way I understand it all the firing buisness tells the tbi to shoot gas, so it can run being bottle fed, making it seem it's a fuel not fire problem. Though the issue is in the ignition system, ?, ain't computers nice. I was ready to change the computer till my old mechanic buddy (been a mechanic since th 70's said those computers don't go out). After hearing all this debate seems they do? I'm thinking climate, or moisture to be more precise. Personally I would fix the TBI, not being able to run a manual pump, seems with todays gas and parts the pump is the weak spot of tbi.

Edit to add. seems there is a plug goes into the coil, maybe, dont remember but in that area that the air breather all but rubs on the wires kink pretty tight. Mine the bottom/ inside of that kink the insulation was broke and allowing those angry pixies to jump around and intermingle.

You must be registered for see images attach

This may not be what you meant but on early 90s tbi (not sure if it applies to the 87 tbi or not) the #7 wire was routed too close to the throttle cable and rubbed through (factory issue) but good thing to call out. When wiring is new and gets crunched up near the firewall and all that, easy to overlook a possible issue down the road (for engineering and the assembly line)
Blind installation (assembly wise) makes for strange issues and Im sure the wiring either went on the engine first or it was put on after in the truck., either way its a long reach and its a out-of-mind/sight area, so great thing to check

 

[mcarlo86]

I was gonna say the same thing. I was diagnosing what ended up being a mechanical issue w/ my 350 TBI, and bought a reconditioned ECM/PROM on evilbay for around $150. The ECM ended up not being my issue (was a flat cam lobe), but I did confirm it worked fine, so now I have a spare in case the current one croaks. Unfortunately these systems are OBD I, and so there are very limited options for troubleshooting, compared to OBD II. However if you have a check engine light on and a paper clip handy, you can get a surprising amount of clues to point in the right direction.

That being said, I may eventually go to a carb setup on mine. The only reason I would switch is to take advantage of a sportier cam/head setup. I've never tried it on a TBI system, but from what I've read it can be a real bear to get them to work with performance cams & heads, but as we well know, not such an issue with a carb setup.

Best of luck - hope you get it figured out either way.

Before you ditch the TBI, read through all the info on this website: https://harristuning.com/Tbi/. Especially the recommendations section for 350 TBI's. There is a lot of good info on that site.

 

[AyWoSch Motors]

Before you ditch the TBI, read through all the info on this website: https://harristuning.com/Tbi/. Especially the recommendations section for 350 TBI's. There is a lot of good info on that site.

Thanks. I just checked it out.
Looked threw a bit, looked at the troubleshooting section. All je said on there about what i got going on is "check your grounds".

 

[gmbellew]

Thanks. I just checked it out.
Looked threw a bit, looked at the troubleshooting section. All je said on there about what i got going on is "check your grounds".

tbimods has some decent info, for sure. especially if you are looking to make mods and more power. but nothing beats the Drive-ability manual from GM if you are messing with a stock system. it is like the Bible on TBI and is available in the reference library on this site.