1987 V10 with 1974 engine- need TBI Help

[JT58]

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.

 

[Ricko1966]

195 is not to hot and definitely worth a try. You need to get wiring schematic and find out why your check engine light doesn't work. Have you checked the bulb?

 

[75gmck25]

195 degrees is the stock thermostat for a ‘74. There is almost zero advantage from using a lower temp thermostat, since it will not help fix a marginal cooling system.

With a 195 degree thermostat in the 350 crate in my ‘75 it runs about 195-200 degrees consistently, which would be a good temp for TBI.

 

[Gander]

Check your throttle body for a vacuum leak at the throttle shaft. The holes in the throttle body itself tend to get wallered out over time and you’ll have a vacuum leak there.

195 degree thermostat isn’t too hot. It’s exactly what you need for TBI. It’ll never get into closed loop if it can’t get up to 195 and that means it’ll run super rich and like dogshit after it’s warmed up. I went through all this on my ‘87 within a couple of months of owning it.

 

[bucket]

Check your throttle body for a vacuum leak at the throttle shaft. The holes in the throttle body itself tend to get wallered out over time and you’ll have a vacuum leak there.

195 degree thermostat isn’t too hot. It’s exactly what you need for TBI. It’ll never get into closed loop if it can’t get up to 195 and that means it’ll run super rich and like dogshit after it’s warmed up. I went through all this on my ‘87 within a couple of months of owning it.

I agree with the first part, but my experience with the thermostat situation is much different. I have run several TBI engines (4.3l through 7.4l) with 180 degree t-stats as daily drivers, including in the winter, and they most certainly always got into closed loop just fine and ran great. Heck, I even ran a 160 stat (installed by PO... I eventually swapped in a 180 for better heat in the winter) in a 305 Camaro for a long while and it had no problems getting into closed loop. It even got a consistent and repeatable 28mpg (on interstate) when running all year.

 

[gmbellew]

For something like idle surging, you really need to be able to see what the ECM is doing with fueling in response to the other sensors.

My guess is it is something related to O2 feedback in closed loop. Could be restricted exhaust, could be O2 sensor going bad/lazy, or any number of things.

Do you have scanning capability?

 

[JT58]

Thanks for the replies. I am not sure if the scanner port works. I have an ODB2 scanner and it does not fit the port. It may be an ODB1 port or what is it? There are no lights on the dash other than the bulb when I turn on the headlights, so check engine light is inoperable. I tried jumping the two ports to reset the idle and they seem to be dead. The truck has the factory exhaust manifolds with the stock cross over pipe and it has the two O2 sensors installed. After the cross over pipe it goes into a single 4 inch exhaust which then splits into dual 3 inch exhaust pipes out the back. No CATS. All factory wiring under the hood is there and in great shape. It does seem to run rich, the exhaust does smell rich.

Would it be worth getting a 195 degree thermostat? Maybe purchasing a complete new TBI unit? I'm afraid after investing in that it still will not idle or run worse. Just getting it diagnosed I'm looking at about 1K at least so a new TBI unit and thermostat is much cheaper and I can easily install them. Vehicle work is horrible crazy expensive where I live. So I do as much work as I possibly can.

Is there a way to check for leaks at the throttle shaft of the throttle body?

 

[JT58]

Also I think the throttle body may be bad...........the connectors to the fuel injectors are all deformed and like melted like there was a fire in the TBI from the previous owner- probably sprayed something flammable in the TBI and probably permanently damaged it. Probably worth getting a new TBI.

 

[gmbellew]

The tbi is all metal…so aside from sensors and injectors and gaskets, it should be rebuildable.

There is a diagnostic for “no SES” light in the drivability manual.

If you jumper AB with key on, it will flash 12s and then any codes followed by 12s, all 3 times each. It will also force the IAC closed (you should hear the stepper motor working).

The port is OBD1. You will need a different cable and either winaldl or tuner pro on a computer or aldldroid and a droid phone if you can find a Bluetooth scan cable. Unless you can see some ECM data, this will be a bit difficult to diagnose and resolve. Even with the data, it still might not be straight forward

 

[JT58]

Well I checked the OBD1 port and the wires are all there. It also appears to be working as when I jump the A and B ports I can hear the IAC stepper motor when I turn the key on. There are no lights though. Maybe bulbs burned out?

I don't have a Droid phone or tuner. What would I need to buy to get some ECM data?

I did order a new TBI and new fuel injector connectors. I figure it can't hurt and this is my forever truck and I'm, retired- I also have so much invested I would never get it back...............

 

[gmbellew]

As a first step, I’d troubleshoot the lack of SES light. Then see if you have codes. If not, I’d look into winaldl and a cable. I think moates has the stuff you need. The place I got my cable from for the droid app is no longer around (1320 electronics)

 

[YakkoWarner]

I bought the cable from Moates last year and use it with an obsolete old laptop running Windows10 and TunerPro RT. It wasn't cheap (around $80 if I recall) but works exactly as advertised.

I agree with the other contributers, figuring out why your SES light is dead is an important 1st step.

 

[Gander]

I agree with the first part, but my experience with the thermostat situation is much different. I have run several TBI engines (4.3l through 7.4l) with 180 degree t-stats as daily drivers, including in the winter, and they most certainly always got into closed loop just fine and ran great. Heck, I even ran a 160 stat (installed by PO... I eventually swapped in a 180 for better heat in the winter) in a 305 Camaro for a long while and it had no problems getting into closed loop. It even got a consistent and repeatable 28mpg (on interstate) when running all year.

Well, all I know is there was a 160 tstat in my truck when I got it and it absolutely wouldn’t go into closed loop that cold. 1987 V10 with 350TBI. Even after I changed a bunch of sensors including the coolant temp sensor. Changing the thermostat got it into closed loop once it got all the way up to temp. I didn’t try 180 though. Factory tstat when the truck was new was 195 and when the ECM software was written it was with the understanding that a 195 tstat would be installed so that’s what I went with. YMMV.

 

[Gander]

Thanks for the replies. I am not sure if the scanner port works. I have an ODB2 scanner and it does not fit the port. It may be an ODB1 port or what is it? There are no lights on the dash other than the bulb when I turn on the headlights, so check engine light is inoperable. I tried jumping the two ports to reset the idle and they seem to be dead. The truck has the factory exhaust manifolds with the stock cross over pipe and it has the two O2 sensors installed. After the cross over pipe it goes into a single 4 inch exhaust which then splits into dual 3 inch exhaust pipes out the back. No CATS. All factory wiring under the hood is there and in great shape. It does seem to run rich, the exhaust does smell rich.

Would it be worth getting a 195 degree thermostat? Maybe purchasing a complete new TBI unit? I'm afraid after investing in that it still will not idle or run worse. Just getting it diagnosed I'm looking at about 1K at least so a new TBI unit and thermostat is much cheaper and I can easily install them. Vehicle work is horrible crazy expensive where I live. So I do as much work as I possibly can.

Is there a way to check for leaks at the throttle shaft of the throttle body?

2 o2 sensors? You sure about that? My 1987 V10 350TBI still had the stock y pipe on it when I got it and there was only 1 o2 sensor.

The injector connectors are super cheap on Amazon, like $10 for the pair. Easy to change out.

There’s a lot of good suggestions on here. You need to get the CEL working, check the bulb first, might be as simple as it being burned out. IAC reset not working could be as simple as the IAC valve is stuck or otherwise bad.

The reality is that TBI is really simple electronic fuel injection but it’s still electronic fuel injection. Everything has to be in good shape to work and any one thing off can throw the whole thing off. Grounds have to be clean and making good contact. No vacuum leaks anywhere, TBI unit needs to be in good shape, no leaks of any kind, clean, good shape. All the sensors AND electrical connectors for those sensors need to be in good shape, all the wiring has to be in good shape. You need to have the CEL working to be able to read codes. You’d have to get all of that working before you’d be able to get to the ECM or OBD1 port and they likely aren’t your problem since you’re describing a whole bunch of problems that would be problems even if the ECM was working perfectly.

 

[JT58]

2 o2 sensors? You sure about that? My 1987 V10 350TBI still had the stock y pipe on it when I got it and there was only 1 o2 sensor.

The injector connectors are super cheap on Amazon, like $10 for the pair. Easy to change out.

There’s a lot of good suggestions on here. You need to get the CEL working, check the bulb first, might be as simple as it being burned out. IAC reset not working could be as simple as the IAC valve is stuck or otherwise bad.

The reality is that TBI is really simple electronic fuel injection but it’s still electronic fuel injection. Everything has to be in good shape to work and any one thing off can throw the whole thing off. Grounds have to be clean and making good contact. No vacuum leaks anywhere, TBI unit needs to be in good shape, no leaks of any kind, clean, good shape. All the sensors AND electrical connectors for those sensors need to be in good shape, all the wiring has to be in good shape. You need to have the CEL working to be able to read codes. You’d have to get all of that working before you’d be able to get to the ECM or OBD1 port and they likely aren’t your problem since you’re describing a whole bunch of problems that would be problems even if the ECM was working perfectly.

Only 1 O2 sensor on the left side manifold, my bad. The ODB1 port is working, I will check for burned bulbs next. I did order a INNOVA 3123 code reader from Amazon. And I ordered the fuel injector connectors from Rock Auto. I tired to order a whole TBI and despite stating "in stock" no one seems to have one. I can rebuild mine but how do I know if the throttle shafts are not too worn and causing a vacuum leak? Can worn throttle shafts be repaired? If I get a used TBI from a scrap yard it might have the same worn shafts.

It definitely seems like I need to change to a 195 degree thermostat. That I can easily do.

I kept my appointment at the local repair vintage shop and will see what they say next week. In the meantime I will do what I can to continue to troubleshoot.....