Vince's TBI woes, progressive revelations, and tbi mods.

[Catbox]

I have been trying to get my 1995 Sub through emissions testing lately and because of that I have been doing quite a bit of reading up on the gizmos that make the TBI run.

I have also figured that with 225K on the parts and pieces that make it up, along with having a kid that now works at a auto parts store with a discount that I will simply replace some of these things out of service life.

We still have not made it through DEQ yet.
Next is a new O2 sensor as I have not changed it in the 17 years I have had it.
Probably way to long to go.
Max got it out a bit ago and found that the last one that was installed, was cross threaded.
So we ordered a O2 thread chaser to clean up the bung...

Nobody likes a dirty bung.

 

[Vbb199]

I have been trying to get my 1995 Sub through emissions testing lately and because of that I have been doing quite a bit of reading up on the gizmos that make the TBI run.

I have also figured that with 225K on the parts and pieces that make it up, along with having a kid that now works at a auto parts store with a discount that I will simply replace some of these things out of service life.

We still have not made it through DEQ yet.
Next is a new O2 sensor as I have not changed it in the 17 years I have had it.
Probably way to long to go.
Max got it out a bit ago and found that the last one that was installed, was cross threaded.
So we ordered a O2 thread chaser to clean up the bung...

Nobody likes a dirty bung.

Ha! Sounds like my luck with my bung on my exhaust

 

[gmbellew]

per the manuals, TPS voltage below 1.25 at throttle closed and above 4.5 for WOT is "OK". but several references are made to the throttle closed voltage of 0.5-0.6v, indicating that is the better target. mine is in the .62-.65 range

the TPS won't throw a code until the voltage is greater than 2.5v for 3 seconds below 1200RPM or unless the circuit is open or shorted to ground.

if you haven't downloaded the manuals from the library, i would recommend it. for TBI they are great resources and they are searchable. pdfs....so they are easy to navigate.

 

[Chevyguy]

per the manuals, TPS voltage below 1.25 at throttle closes and above 4.5 is "OK". but several references are made to the throttle closed voltage of 0.5-0.6v, indicating that is the better target. mine is in the .62-.65 range

the TPS won't throw a code until the voltage is greater than 2.5v for 3 seconds below 1200RPM or unless the circuit is open or shorted to ground.

if you haven't downloaded the manuals from the library, i would recommend it. for TBI they are great resources and they are searchable. pdfs....so they are easy to navigate.

Mine didn't throw a code. I just watched the voltage go from .68 to 1.28 volts as I slowly pressed on the accelerator pedal. My Scan tool has paid for it's self because it allow's you to see the sensors in live action. My new TPS sensor voltage read at .5v with the throttle closed.

Clayton

Sent from my SM-A705U using Tapatalk

 

[Vbb199]

So i bought one of these bad boys. Waiting on it to arrive.


https://www.ebay.com/itm/274172878497

Then i can get actual datalogging.


On another note @Chevyguy and @gmbellew i was studying the TPS some more today.

I noticed input voltage was 4.4v, and when i unplugged the sensor and checked the plug, i got 4.97 volts. Weird.
I noted that idle sat at .66 or whatever volts, but at WOT i got 4.4 or something also.


By turning the truck off, and manually actuating the TPS to "WOT" i could get as much as 4.7v.


Then TODAY, while sitting at the atm, i gave the engine light pedal, the motor revved up, gave it slightly more, revved higher (we are talking less than 1500 rpms) then suddenly, i heard the timing advance randomly, which in turn the motor suddenly got alot more rowdy sounding.

After that, i became fully convinced my TPS is junk.
I ordered a new one from the local parts house. It will arrive tomorrow, and i can then test my theory.

 

[gmbellew]

the difference between WOT using the pedal and the actual throttle under the hood could be in the linkage or something (ie, carpet thickness...).

keep us posted on the TPS. it is one of the few sensors I haven't replaced on mine yet.

make some posts on data logging. i have never done it, because i don't know what I am doing.

 

[Chevyguy]

So i bought one of these bad boys. Waiting on it to arrive.


https://www.ebay.com/itm/274172878497

Then i can get actual datalogging.


On another note @Chevyguy and @gmbellew i was studying the TPS some more today.

I noticed input voltage was 4.4v, and when i unplugged the sensor and checked the plug, i got 4.97 volts. Weird.
I noted that idle sat at .66 or whatever volts, but at WOT i got 4.4 or something also.


By turning the truck off, and manually actuating the TPS to "WOT" i could get as much as 4.7v.


Then TODAY, while sitting at the atm, i gave the engine light pedal, the motor revved up, gave it slightly more, revved higher (we are talking less than 1500 rpms) then suddenly, i heard the timing advance randomly, which in turn the motor suddenly got alot more rowdy sounding.

After that, i became fully convinced my TPS is junk.
I ordered a new one from the local parts house. It will arrive tomorrow, and i can then test my theory.

I agree with you. Your TPS is bad. Good job on your diagnosis. Looking forward to seeing how your laptop scantool setup works out once you receive it.

Clayton

Sent from my SM-A705U using Tapatalk

 

[Vbb199]

the difference between WOT using the pedal and the actual throttle under the hood could be in the linkage or something (ie, carpet thickness...).

keep us posted on the TPS. it is one of the few sensors I haven't replaced on mine yet.

make some posts on data logging. i have never done it, because i don't know what I am doing.

I agree with you. Your TPS is bad. Good job on your diagnosis. Looking forward to seeing how your laptop scantool setup works out once you receive it.

Clayton

Sent from my SM-A705U using Tapatalk

I will keep you gentlemen posted. I can do the logging from my phone actually, and view the data there, or pull it up on the pc.

 

[Vbb199]

the difference between WOT using the pedal and the actual throttle under the hood could be in the linkage or something (ie, carpet thickness...).

keep us posted on the TPS. it is one of the few sensors I haven't replaced on mine yet.

make some posts on data logging. i have never done it, because i don't know what I am doing.

And in regards to this, simulating WOT on the TPS, i got the 4.7v, simulating WOT on the throttle bodies actual throttle arm, i got 4.4, the physical arm was at its limit.

i should've been more clear, sorry.

 

[Chevyguy]

And in regards to this, simulating WOT on the TPS, i got the 4.7v, simulating WOT on the throttle bodies actual throttle arm, i got 4.4, the physical arm was at its limit.

i should've been more clear, sorry.

No worries, I was looking more at the voltage with the throttle closed. You did a good job.

Clayton

Sent from my SM-A705U using Tapatalk

 

[Slybeanx]

Im patiently waiting on a new PROM chip for my truck... will boost hp and tq 35 points min as well as delete the egr circuit, following that ill block it off with a plate i machine up.........

Im not giving it a whole lot if thought until the chip arrives.... but your thoughts are on track with mine there.

I found this thread while browsing the forum. Why dont you run Megasquirt on the truck? It'd run the engine no problem and youll never need to deal with chips again?

 

[Vbb199]

I found this thread while browsing the forum. Why dont you run Megasquirt on the truck? It'd run the engine no problem and youll never need to deal with chips again?

I have looked into different ecm types.( if thats what that is), i was looking at Dynamic EFI also.


Sorry i missed your reply i didnt know you commented, weird.

 

[Vbb199]

So, last night @Chevyguy @gmbellew i installed the new TPS, mounting holes were .200", i drilled them to .250 for wiggle room. Set it at like, .60V at idle...WOT was coming up as 4.5...

Same gig as before though, harness unplugged, i had 4.97v, plugged into TPS, i got 4.5v......

Suggestions? I assumed thr range of 4.5-5.0v wot was acceptable?

 

[Vbb199]

On another note.... i think i found my issue lol.

I grounded out the ALDL, turned the key on, putting it into diagnostic mode, thus allowing the IAC pintle to fully extend, unplugged the IAC.... fired the truck up.... it idles where i set it last (not high like when iac is plugged in).. ok... all good... issue is.... truck runs fine with IAC unplugged... no SES, no nothing.. doing great.


So therefore, im to assume i have a vacuum leak somewhere... last night, while the truck was running i carefully sprayed Carb Cleaner all over vacuum lines, around the intake and TB, my EGR blockoff i made, the vacuum ball, the carbon canister or whatever... Nothing... now im REALLY confused wtf is up...

My theory in a vacuum leak is odd... i see no evidence of a leak with a vacuum gauge... but this morning, it was below freezing outside.. go to fire it up, turns right off... ok. Try again, its idling really low, wick the throttle twice, truck idles fine... while im pouring my AM coffee i hear the idle occasionally surging slightly by say, 500 rpms or less.... no doubt a leak exists since the "controlled leak" (IAC) is "capped off"



Scan tool /datalogger arrives today.
i will then have the ability to pull hard data and SEE what is UP!

 

[gmbellew]

So, last night @Chevyguy @gmbellew i installed the new TPS, mounting holes were .200", i drilled them to .250 for wiggle room. Set it at like, .60V at idle...WOT was coming up as 4.5...

Same gig as before though, harness unplugged, i had 4.97v, plugged into TPS, i got 4.5v......

Suggestions? I assumed thr range of 4.5-5.0v wot was acceptable?

Per the manual, I think anything above 4.5 at WOT is ok.