TBI and low MPG advice

[lothar863]

I also installed my tailgate net

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[bucket]

So code 24 and 44, VSS and then the O2 sensor thinks the engine is running lean.

@Rusty Nail that's what a 454 throttle body looks like.

 

[lothar863]

So code 24 and 44, VSS and then the O2 sensor thinks the engine is running lean.

@Rusty Nail that's what a 454 throttle body looks like.

I just replaced the TPS. this one appeared adjustable. i might need to adjust it or is there something i need to do to clear the codes.

The headers came in and i will be dropping the truck off to get it's new exhaust and OS sensor starting monday.

 

[lothar863]

So code 24 and 44, VSS and then the O2 sensor thinks the engine is running lean.

@Rusty Nail that's what a 454 throttle body looks like.

never mind 24 is the speed sensor. where is that located.

 

[bucket]

It's on the back of the speedo, as '89 was the last of the cable-driven speedos. If your speedo ccable is broken or unhooked, you will get the code 24.

 

[Rusty Nail]

Thanks. Good pix!
Unhooking your battery cable will clear the codes.

 

[lothar863]

It's on the back of the speedo, as '89 was the last of the cable-driven speedos. If your speedo ccable is broken or unhooked, you will get the code 24.

I had it unhooked. I have it hooked up now and the speedo and the cruise control is working. I am pretty sure i also had a coolant temp sensor code. While i was doing all of this i also replaced the coolant temp sensor with a new one.

I am going to have the exhause place delete the air pump when they put the headers on and install the new o2 sensor. Maybe then i will get more than 4mpg

 

[lothar863]

New exhuast is on and the new o2 sensor is installed. It is way down stream from the factory location so plans for a 4 wire swap in the future.

I got 12.5 mpg over 80 miles yesterday.

I am still idling at 1500-2000 though.

 

[4WDKC]

New exhuast is on and the new o2 sensor is installed. It is way down stream from the factory location so plans for a 4 wire swap in the future.

I got 12.5 mpg over 80 miles yesterday.

I am still idling at 1500-2000 though.

This could be a result of an exhaust leak or needing to re calibrate/learn the IAC. insert jumper wire like to read codes, wait 5 sec. go disconnect IAC, turn key off. Remove jumper, re connect IAC..start truck, you may have to give it gas to get it to start but then it will relearn and start/idle with no issue assuming no leaks.

 

[Daveo91Burb]

Also check for vacuum leaks. I’m running that same adapter between the TB and intake that you have and I’m concerned it’s warped. (check out my vacuum leak post that’s active on the forum now). With everything bolted back up and engine idling, spray carb cleaner around all the gasket sealing surfaces. If RPM changes noticeably you are sucking air someplace you’re not supposed to. Vacuum leaks can affect TBI idle and decel on TBI, as I’m finding out!

 

[Rusty Nail]

Yeah but it's normally at the throttle shaft bushings...

 

[lothar863]

Also check for vacuum leaks. I’m running that same adapter between the TB and intake that you have and I’m concerned it’s warped. (check out my vacuum leak post that’s active on the forum now). With everything bolted back up and engine idling, spray carb cleaner around all the gasket sealing surfaces. If RPM changes noticeably you are sucking air someplace you’re not supposed to. Vacuum leaks can affect TBI idle and decel on TBI, as I’m finding out!

Sprayed starting fluid all around the TBI while running and no change in the RPM.

I haven't done the IACV relearn like suggested yet but I will.
I think I will also benefit from a 4 wire o2 sensor since the o2 sensor is now so much further back in the exhaust.
You can see the exhaust here:
https://www.gmsquarebody.com/threads/clifford-the-big-red-truck.24471/page-2#post-475141

 

[DBurns007]

Did you get the TPS installed properly on this truck? From memory I believe you should be at .5 volts with no throttle and 4.8 to 5volts at wide open throttle.. also.. is the factory plug for the idle screw on the throttle body missing? If it is, I’m assuming someone made a manual adjustment to idle, which should not be done.

I’m asking in reference to the high idle symptom..

Danny.

As you probably know.. the voltage can be checked with key on engine off or with a obd1 capable scanner.. DVOM will work just fine.


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[bucket]

Did you get the TPS installed properly on this truck? From memory I believe you should be at .5 volts with no throttle and 4.8 to 5volts at wide open throttle.. also.. is the factory plug for the idle screw on the throttle body missing? If it is, I’m assuming someone made a manual adjustment to idle, which should not be done.

I’m asking in reference to the high idle symptom..

Danny.

As you probably know.. the voltage can be checked with key on engine off or with a obd1 capable scanner.. DVOM will work just fine.


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While the idle screw should not have been touched 30 years ago, it is often required on an older vehicle to compensate for wear. Even with a properly working IAC, the base idle speed needs to be properly set as well.

 

[DBurns007]

While the idle screw should not have been touched 30 years ago, it is often required on an older vehicle to compensate for wear. Even with a properly working IAC, the base idle speed needs to be properly set as well.

I agree with you on curb idle.. however, I was suggesting it was possible that someone unknowingly tried to adjust idle outside of procedure and caused a high TPS signal at idle which would most certainly affect idle speed at 0% throttle position. I was asking because at some point he had a high voltage code for TPS.. at least I think he did?




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