TBI and low MPG advice

[chengny]

Fuel filter was replaced along with cap, rotor, wires, and coil.
Every time i have put gas in it i have added a bottle of Lucas injection fuel treatment with it.
Nothing is around the flex plate.

I have the plugs i just couldn't locate them when i was doing the tune-up items.
I also havent checked the timing.
I have a timing light somewhere i will just need to find it
It sounds like the timing should be at 4 degrees stock but where is the best place to set the base timing for economy?
Also could someone link me how to get it to where I can set the base timing?

Also where does the ecm pull data for the fuel map on these?

As far as i can see i am not finding an O2 sensor in the exhaust.
Should there be one?

Does it pull from other sensors? RPM? Speed? TPS?
I do not have the speedo cable hooked up because the shop had the connection clocked the wrong way and i haven't got under the truck to rotate it back.

A little background I have always dealt with newer more electronic vehicles so I am a bit out of my element on it but trying to get up to speed.

It's hard sometimes to help a guy diagnose poor engine performance over the internet. Usually because the facts are delivered in dribs and drabs, but also the fact that you don't know him (or his capabilities) hinders the diagnostic procedure. So you often end up getting a broad spectrum of crazy possible causes -like mice living in the tail pipe for example.

Maybe you should start at the beginning?

1. If you turn the ignition switch to RUN, is there an illuminated SES warning light showing on the dash?

2. If there is, does it go away when the engine is cranked and fires up?

 

[lothar863]

It's hard sometimes to help a guy diagnose poor engine performance over the internet. Usually because the facts are delivered in dribs and drabs, but also the fact that you don't know him (or his capabilities) hinders the diagnostic procedure. So you often end up getting a broad spectrum of crazy possible causes -like mice living in the tail pipe for example.

Maybe you should start at the beginning?

1. If you turn the ignition switch to RUN, is there an illuminated SES warning light showing on the dash?

2. If there is, does it go away when the engine is cranked and fires up?

When i turn the key i get a brake and a fasten seat belt light and both go off after a couple seconds when the engine is started.
I do not recall a check engine light but I can check tonight and get a video of the dash during key turn and first startup if it would be helpful.

 

[MrMarty51]

89 year is OBD1, cross the A and B pins in the ALDL connector, see if any codes comes up.
How is the idle ? rough like a carbed engine with the choke pulled on ?
O2 sensor may located in either exhaust manifold, if not it will be right below the exhaust pipe to manifold flange. For no more than what an O2 sensor costs, might just replace it. Most people I know with the 454 in a larger truck gets 12 to 14 MPG. without a load.

 

[bucket]

If the fuel pump gets weak, it can still run somewhat ok, but have terrible performance and economy. TBI can run on as little as 6 psi, it will just be sluggish and miss/stumble under load.

The MAP sensor and TPS play a very large part in the ECM knowing how much load the engine is seeing.

 

[chengny]

When i turn the key i get a brake and a fasten seat belt light and both go off after a couple seconds when the engine is started.
I do not recall a check engine light but I can check tonight and get a video of the dash during key turn and first startup if it would be helpful.

What those guys above said makes my point. If the truck is running like you say, the ECM is almost surely throwing DTC's. But, if the bulb is burned out, you'd never know.

Like Marty says, make a little jumper out of a paper clip bent into a U-shape. Turn the key to RUN (not started) and insert the clip into the ALDL socket as shown:

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First check is that the diagnostic system is functional. That is proven by a 12 code - that is if the SES light is not burned out. A 12 code is: one flash, a brief pause and then two flashes. It will repeat 3 times. And then, if any other DTC's are stored, they will subsequently be flashed. Have a paper and pen handy.

 

[bucket]

I certainly agree that the engine light needs to be operational to check for codes and help diagnose. But I wouldn't be surprised if there's no codes stored. The TBI ecm's are extremely stupid sometimes, they can have issues that make them run like dog poo, but the ecm won't know enough of what's going on to set a code.

 

[Shorty81]

Try advancing timing to 8 to 10 degrees. My BB likes advanced timing.

 

[lothar863]

I certainly agree that the engine light needs to be operational to check for codes and help diagnose. But I wouldn't be surprised if there's no codes stored. The TBI ecm's are extremely stupid sometimes, they can have issues that make them run like dog poo, but the ecm won't know enough of what's going on to set a code.

So the bulb wasnt bad but i think the circuit board is going bad. I wiggled it and i was able to get codes.

If i read it correctly I got a
12
13
14

I then put the dash back together and the bulb wasnt working again or i would have a video to make sure i was interrupting it right.

So there is an O2 sensor it is in the manifold on the driver side. It looks old and i see some soot on one side like there was/is an exhaust leak there.

If I looked up those codes right
13. Oxygen O2 Sensor – Circuit open/no activity
14. Coolant Temperature sensor – Too High resistance or shorted circuit

I was referencing this site:
https://mechanicbase.com/trouble-code/obd1-codes/

So it looks like I will be ordering
ACDELCO 213928
ACDELCO AFS21

 

[4WDKC]

So the bulb wasnt bad but i think the circuit board is going bad. I wiggled it and i was able to get codes.

If i read it correctly I got a
12
13
14

I then put the dash back together and the bulb wasnt working again or i would have a video to make sure i was interrupting it right.

So there is an O2 sensor it is in the manifold on the driver side. It looks old and i see some soot on one side like there was/is an exhaust leak there.

If I looked up those codes right
13. Oxygen O2 Sensor – Circuit open/no activity
14. Coolant Temperature sensor – Too High resistance or shorted circuit

I was referencing this site:
https://mechanicbase.com/trouble-code/obd1-codes/

So it looks like I will be ordering
ACDELCO 213928
ACDELCO AFS21

if those codes are right you could have damaged the catalytic convertor with the excess unburned fuel causing it to clog, if it has been removed thats obviously not the case, but those two things you listed will cause bad mpg. also you said there is soot on the outside of the manifold? That is a sign of an exhaust leak and can make the o2 read incorrectly.

 

[lothar863]

if those codes are right you could have damaged the catalytic convertor with the excess unburned fuel causing it to clog, if it has been removed thats obviously not the case, but those two things you listed will cause bad mpg. also you said there is soot on the outside of the manifold? That is a sign of an exhaust leak and can make the o2 read incorrectly.

there are exhaust leaks at every joint and the exhaust is not factory. There are 2 cats and a muffler.

The exhaust leak i was mentioning was a black soot mark on the side of the O2 sensor making me think that was a leak as well.

I ordered the new O2 and coolant temp sensor.

I am planing on all new exhaust and deleting the smog pump.

My thoughts are possibly these headers
https://www.amazon.com/dp/B000CO7KK...olid=25RY9YMS636RZ&psc=0&ref_=lv_ov_lig_dp_it

True dual exhaust with an h pipe and one of these on each pipe
https://www.amazon.com/dp/B000CNLAX...olid=25RY9YMS636RZ&psc=0&ref_=lv_ov_lig_dp_it

and have each side dump before the dually fender flares on each side.

 

[4WDKC]

there are exhaust leaks at every joint and the exhaust is not factory. There are 2 cats and a muffler.

The exhaust leak i was mentioning was a black soot mark on the side of the O2 sensor making me think that was a leak as well.

I ordered the new O2 and coolant temp sensor.

I am planing on all new exhaust and deleting the smog pump.

My thoughts are possibly these headers
https://www.amazon.com/dp/B000CO7KK...olid=25RY9YMS636RZ&psc=0&ref_=lv_ov_lig_dp_it

True dual exhaust with an h pipe and one of these on each pipe
https://www.amazon.com/dp/B000CNLAX...olid=25RY9YMS636RZ&psc=0&ref_=lv_ov_lig_dp_it

and have each side dump before the dually fender flares on each side.

The exhaust needs to fixed to find out what the o2 is seeing, I wouldnt put a new o2 sensor in the leaky system it.

 

[Jppr26]

I recently got a tbi from a wrecking yard for my 87 tbi 350 and rebuilt it, ground down the air dams, and polished it up, haven't checked mpg but have noticed a immediate difference

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[gotyourgoat]

Have you checked the cats to see if they are restricting flow? You mentioned earlier it seemed like a healthy flow out the pipes but sitting in a driveway is different than on the road.

 

[lothar863]

So here are some videos of the codes

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[lothar863]

I rebuilt the throttle body and installed the spacer.

I also broke the injector housing. I epoxied it and it is holding so far but does anyone have a spare they are willing to part with?

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