1987 V10 with 1974 engine- need TBI Help

gmbellew said:

I’d probably not mess with the base idle until after you have a peek at what the ECM is seeing and doing with fuel. But otherwise,yeah, just hook everything back up and fire it up

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OK thanks- installation planned for Monday 4/19. I'll respond with how I make out and will check for any codes from the ECM. The TBI was from a company called Autoline products. I bought from Autozone but Rock had the same exact unit for $100 cheaper but lead time was 1.5 weeks. Autozone was only 2 days. Unit was nicely packaged and looked absolutely brand new. I could find the TBI only from Autozone or Rock Auto. No one else had it.

Today's update- I replaced the fuel injection connectors. They were so brittle and burned they practically disintegrated. Took the TBI off. A couple of observations......the top portion of the TBI where the fuel injectors are was extremely loose. Gasket appears to be good, it's like it was never tightened. The TBI gasket itself was no good, it was not sealed on the intake. There was no O Ring on the return fuel line. I had to order the O Ring- fortunately O Reillys had it- 1 day away.

So now knowing this- do I re-install the old TBI with new gasket and O Ring so it is sealed and give it a go before I try the new one? If it works I could return the new one and save $622. The only thing to risk is needing a second TBI gasket.

JT58 said:

Today's update- I replaced the fuel injection connectors. They were so brittle and burned they practically disintegrated. Took the TBI off. A couple of observations......the top portion of the TBI where the fuel injectors are was extremely loose. Gasket appears to be good, it's like it was never tightened. The TBI gasket itself was no good, it was not sealed on the intake. There was no O Ring on the return fuel line. I had to order the O Ring- fortunately O Reillys had it- 1 day away.

So now knowing this- do I re-install the old TBI with new gasket and O Ring so it is sealed and give it a go before I try the new one? If it works I could return the new one and save $622. The only thing to risk is needing a second TBI gasket.

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I would reinstall the existing one with proper gaskets and see how it does....

So I reinstalled the original one with the proper gaskets and O Rings and there was no improvement- disappointing. I then installed the new one and at start up it was very smooth, good and steady fast idle. The truck also ran really good with better throttle response than it ever had before. Then the hot idle was way too high and I tried the idle set procedure. It would not start with the IAC unplugged, it idled too low to run. So I plugged the IAC back in and re-adjusted the idle screw to get it to idle. So now when I start it hot the idle is very low then it gets higher as it runs. The idle is better than it was with the old TBI but it still hunts and still smells like it runs rich. There are no vacuum leaks that I am aware of- unless it's in the brake booster. Anything but idle the engine runs so great. I'm getting frustrated and not sure what to do next. Could it be a voltage issue or the ECM is faulty? Should I disconnect the battery and let the ECM clear out?

It's in a good state to bring to the classic repair shop now with the SES light fixed and new TBI but they do charge a fortune.

Unless the shop has a scan tool, I don’t know what they will do for you if there are no codes.

Seeing what the ECM sees and how it is adjusting fueling is needed to help. And that still isn’t a silver bullet.

If it idles cold fine, but hunts in closed loop, it is something the O2 sensor is seeing that is making it hunt or something that is messing with the ECM (stray voltage, EMI, etc causing extra reference pulses or something).

Is the exhaust new? If not the cat might be plugged or clogged.

Are all the ignition components new for in good shape? cap, rotor, wires, coil? Mist things down and see if anything sparks.

Are plug wires routed away from sensor and ECM wires?

Check again for vacuum leaks?

Breath, you'll get there.
Unless that shop works specifically with old TBI, not sure they'll know what to do.
All here will help. Get your codes...they will tell you if running rich and maybe o2 sensor.
Make notes and follow these guys instructions, enjoy the journey.

gmbellew said:

Unless the shop has a scan tool, I don’t know what they will do for you if there are no codes.

Seeing what the ECM sees and how it is adjusting fueling is needed to help. And that still isn’t a silver bullet.

If it idles cold fine, but hunts in closed loop, it is something the O2 sensor is seeing that is making it hunt or something that is messing with the ECM (stray voltage, EMI, etc causing extra reference pulses or something).

Is the exhaust new? If not the cat might be plugged or clogged.

Are all the ignition components new for in good shape? cap, rotor, wires, coil? Mist things down and see if anything sparks.

Are plug wires routed away from sensor and ECM wires?

Check again for vacuum leaks?

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The old TBI hunted in closed loop- but still idled, and it idled fine on fast idle. The new one it starts with very low idle now, have to give it gas to keep it running. Then when it warms up the idle is high and will not go down in closed loop. Around 1400 RPM.

No vacuum leaks, new plug wires routed neatly in holders and away from sensors. It has factory manifolds with one O2 sensor in drivers side, stock cross over pipe then 3" duals out the back, no CAT. It also has no smog pump or the manifold smog pipes. Could that be the issue- running a 1974 engine with 1974 heads and TBI intake manifold and electronics from a 1987?

It actually ran better and idled with hunting with the old TBI. I have a $100 core on the new TBI, not sure if I should put the old TBI back on and leave it to hunt and just set the new one aside.

The shop I normally go to is good with older systems. They solved my dual tank issue, which two other shops were not able to. It needed a complete new wiring harness, cost was in the thousands though.

JT58 said:

The old TBI hunted in closed loop- but still idled, and it idled fine on fast idle. The new one it starts with very low idle now, have to give it gas to keep it running. Then when it warms up the idle is high and will not go down in closed loop. Around 1400 RPM.

No vacuum leaks, new plug wires routed neatly in holders and away from sensors. It has factory manifolds with one O2 sensor in drivers side, stock cross over pipe then 3" duals out the back, no CAT. It also has no smog pump or the manifold smog pipes. Could that be the issue- running a 1974 engine with 1974 heads and TBI intake manifold and electronics from a 1987?

It actually ran better and idled with hunting with the old TBI. I have a $100 core on the new TBI, not sure if I should put the old TBI back on and leave it to hunt and just set the new one aside.

The shop I normally go to is good with older systems. They solved my dual tank issue, which two other shops were not able to. It needed a complete new wiring harness, cost was in the thousands though.

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If it is worse with the new TBI, then there are some issues there.

It makes me wonder if the idle stop screw is way out of adjustment or something. But I’d think the IAC would be able to adjust for that, just the counts would be off. If you could scan, you could see IAC counts and have an idea if something is off. High IAC counts would mean the throttle stop is too closed. Low IAC counts mean the throttle stop is too open. Warm idle should be in the 5-30 range.

But if you are idling too low when cold (not enough air past blades and IAC) and idling too high when warm (too much air past blades and IAC), those seem to be opposite issues unless something else is happening as the engine warms up (vacuum leak when warm only?)

gmbellew said:

If it is worse with the new TBI, then there are some issues there.

It makes me wonder if the idle stop screw is way out of adjustment or something. But I’d think the IAC would be able to adjust for that, just the counts would be off. If you could scan, you could see IAC counts and have an idea if something is off. High IAC counts would mean the throttle stop is too closed. Low IAC counts mean the throttle stop is too open. Warm idle should be in the 5-30 range.

But if you are idling too low when cold (not enough air past blades and IAC) and idling too high when warm (too much air past blades and IAC), those seem to be opposite issues unless something else is happening as the engine warms up (vacuum leak when warm only?)

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I am out of ideas. I don't have a scan tool. I tried re-setting the IAC and idle and it was too low and stalling. I can get it to idle nicely with the IAC un plugged. When I plug it back in it's lower- too low, stalling. I repeat the process and raise the idle, it seems fine, then shut it off and re-start it and then it's super high again. The idle is so erratic with the new TBI- low one minute, then high the next. The only other time in my life I had this kind of issue was in a 97 Jeep Wrangler. I could not diagnose the issue, finally gave up brought it to a good shop. It was the ECM. They replaced it and all issues resolved immediately. I can't keep throwing parts at it- I have replaced the EGR, MAP sensor, Throttle Position Sensor, IAC on the old TBI. Then got a new rebuilt TBI with new IAC and throttle position sensor installed.

JT58 said:

I am out of ideas. I don't have a scan tool. I tried re-setting the IAC and idle and it was too low and stalling. I can get it to idle nicely with the IAC un plugged. When I plug it back in it's lower- too low, stalling. I repeat the process and raise the idle, it seems fine, then shut it off and re-start it and then it's super high again. The idle is so erratic with the new TBI- low one minute, then high the next. The only other time in my life I had this kind of issue was in a 97 Jeep Wrangler. I could not diagnose the issue, finally gave up brought it to a good shop. It was the ECM. They replaced it and all issues resolved immediately. I can't keep throwing parts at it- I have replaced the EGR, MAP sensor, Throttle Position Sensor, IAC on the old TBI. Then got a new rebuilt TBI with new IAC and throttle position sensor installed.

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When you say “unplug” do you mean the electrical connection or removing the IAC from the TB?

Is the electrical connection tabs not broken so that you are sure the plug is going on properly?

If you are sure the IAC is plugged in properly, you might try:

1) jumping AB on ALDL and turn ignition on for 1min. Disconnect IAC harness.
2) turn ignition off, remove jumper
3) try to start the vehicle
4a) if it starts and idles fine, close the idle stop screw until the the engine just begins to bog. Then open it back up just a little. Turn off the engine, reconnect the IAC, and see how it does.
4b) if it won’t start, open up the idle stop screw a little at a time until it will. The idle will be low, but that is ok. The IAC will be able to open some and control it once it is reconnected. If you have a tach hooked up, you want the idle around 425-450ish RPM with IAC closed. Once you get it to start and it will barely hold a low idle, turn off engine and reconnect IAC and see how it does.

gmbellew said:

If you are sure the IAC is plugged in properly, you might try:

1) jumping AB on ALDL and turn ignition on for 1min
2) turn ignition off, remove jumper
3) unplug IAC connector (IAC should be closed and all air is passing by the blades.
4) try to start the vehicle
5a) if it starts and idles fine, close the idle stop screw until the the engine just begins to bog. Then open it back up just a little. Turn off the engine, reconnect the IAC, and see how it does.
5b) if it won’t start, open up the idle stop screw a little at a time until it will. The idle will be low, but that is ok. The IAC will be able to open some and control it once it is reconnected. If you have a tach hooked up, you want the idle around 425-450ish RPM with IAC closed. Once you get it to start and it will barely hold a low idle, turn off engine and reconnect IAC and see how it does.

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Actually that procedure needs a slight modification. When you jumper the A/B for a minute, disconnect the IAC connector before turning the key off. Otherwise the computer re-opens the IAC on key-off to allow easier starting.

YakkoWarner said:

Actually that procedure needs a slight modification. When you jumper the A/B for a minute, disconnect the IAC connector before turning the key off. Otherwise the computer re-opens the IAC on key-off to allow easier starting.

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I know it opens it with key on for sure. It might also open it with key off using the constant power to the ECM, good catch and better safe than sorry. I will edit.

gmbellew said:

I know it opens it with key on for sure. It might also open it with key off using the constant power to the ECM, good catch and better safe than sorry. I will edit.

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Yeah, iirc, the IAC opens up all the way when the ignition is shut off.

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.