89 GT stumbles 2500 and above

Dtambs39

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Feb 25, 2021
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I checked just the voltage on the TPS, yes it was a digital tester. What should the resistance be for it?
Whats a good brand of TPS, ?
Thanks
 
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Bree

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Unplug it and remove it from the car. Take it the workbench and turn it upside down. Connect the leads from the volt/ohm meter (set to ohms not volts!) to any 2 posts on the TPS plug. (there should be 3 total) You will see a notch were the throttle body turns it. Stick a slotted screwdriver in the slot and turn it very slowly. The numbers are not super important. What we are looking for is the needle on the meter should start at, or near zero, and climb as you turn the screwdriver. Watch for the needle to drop or twitch. If it does, you found your dead spot. If not, move the leads to another set of posts in the plug and try again. I usually start with the 2 outside posts, then reverse the leads, then I camp the black one to the center lead, and the red one to the left post, then swap it to the right post, then if I still don't get anything, put the red on the middle post and go left and right with the black lead. Now, some of those posts will be open across them from the start, it's just the ones that do move the needle should move it steady and evenly, no hickups of any kind.
I use an analog meter because the drop/twitch can be very subtle. On a digital meter you could be watching the ohms climb,,, 1.0 1.2 1.3 1.4 ect.... (totally random numbers for the sake of demonstration BTW. Again, the steady climb is what's important.) and if the dropout occurs say between 1.3 and 1.4, it could simply appear and the display as the difference between the numbers clicking between .3 and .4. This is why we use an old school analog meter for this.
Think of a TPS like the volume control knob on old school stereo. Now imagine as you turn up the volume, you have a wonky place in the control knob. If your car stutters around 2500, then that would be like your volume knob stuttering at around 4.5.
 
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Dtambs39

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Feb 25, 2021
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Todays update Checked the fuel pressure it was a steady 42lbs. I couldn't reach the fender so I didn't take it for a drive, Also ordered a new MAF should be in tomorrow.
 

General karthief

wonder how much it would cost to ship you a pair
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Did I not post the checklist?
Let's see :runaway:
Yup, sure did. In the checklist (I believe) is the proper way to check the fuel pressure amongst other things like how to check the maf sensor.
So if you bought the maf and not the sensor you wasted your money.
If you bought the sensor without testing it you are dancing down the repair road throwing money in the air.
Methodical testing, you will likely find that 'oh my god I can't believe that's all it was' moment
 

Dtambs39

Member
Feb 25, 2021
23
2
13
50
Dallas
Did I not post the checklist?
Let's see :runaway:
Yup, sure did. In the checklist (I believe) is the proper way to check the fuel pressure amongst other things like how to check the maf sensor.
So if you bought the maf and not the sensor you wasted your money.
If you bought the sensor without testing it you are dancing down the repair road throwing money in the air.
Methodical testing, you will likely find that 'oh my god I can't believe that's all it was' moment
I posted about the MAF sensor and my testing but did not hear back from anyone? I can't drive down the street with the fuel pressure hanging out the hood. The hose is only 18" long. Whats the way to accomplish this because I am stumped on checking the fuel pressure while driving
Thanks
 

7991LXnSHO

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If you read the checklist part about fuel pressure checking, I do not think you will find it mentions while driving. I’ve do that with a carb, but cir. 39 lbs is a different deal. There is a procedure for a restricted flow fitting and a safer line for a remote mounted gauge. An electric sender sounds like a better long term solution to me.
 

Dtambs39

Member
Feb 25, 2021
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ok now about the MAF readings I posted? any conclusive info from them?
So updates on testing MAF holds 6 volts at idle, on ohms it only 3.97 I read that it should be 10 correct?
Also what about the 42 lbs fuel pressure, Good ?

Best
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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The olm reading is not good, if you tested it correctly, check and clean the connections and retest,
Keep in mind that you can't focus on one component, you have to do the checklist step by step.
 

Dtambs39

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Feb 25, 2021
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Todays update, I changed the TPS in the car and set it for one volt. What a big difference, it solved about 85% of the stumbling issue. Still have a slight hiccup at 3k and again at 4.5k, beside that the tach sweeps pretty steady. First time in over a year I can actually step on the gas and it goes. I also did an adjustment on the TV cable it was almost 1/2" stretched out. Trans shifts much better. So I am just trying to get some input on the MAF sensor. The resistance is low and might be another reason why the entire stumble did't go away,

Best
 

Dtambs39

Member
Feb 25, 2021
23
2
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50
Dallas
If you read the checklist part about fuel pressure checking, I do not think you will find it mentions while driving. I’ve do that with a carb, but cir. 39 lbs is a different deal. There is a procedure for a restricted flow fitting and a safer line for a remote mounted gauge. An electric sender sounds like a better long term solution to me.
Hi I retested the fuel pressure today sits at 42lbs idle and 50lbs idle vacuum off the regulator. The question is that when I turn off the car the fuel pressure drops steadily to 10lbs. I know that I checked the regulator and its dry. The car runs just fine should I not worry about it for now? The only other options are injectors and Fuel pump.
Thoughts?
Best
 

General karthief

wonder how much it would cost to ship you a pair
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32ish at idle with vacuum line on
42+ish at idle with vac line off and plugged
The pressure drop when you turn the key off is not really a concern,
When you rev it up a little the pressure should rise to 42-4ish and not fluctuate.
JMO and this is how my fuel pump readings were
 
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Dtambs39

Member
Feb 25, 2021
23
2
13
50
Dallas
Unplug it and remove it from the car. Take it the workbench and turn it upside down. Connect the leads from the volt/ohm meter (set to ohms not volts!) to any 2 posts on the TPS plug. (there should be 3 total) You will see a notch were the throttle body turns it. Stick a slotted screwdriver in the slot and turn it very slowly. The numbers are not super important. What we are looking for is the needle on the meter should start at, or near zero, and climb as you turn the screwdriver. Watch for the needle to drop or twitch. If it does, you found your dead spot. If not, move the leads to another set of posts in the plug and try again. I usually start with the 2 outside posts, then reverse the leads, then I camp the black one to the center lead, and the red one to the left post, then swap it to the right post, then if I still don't get anything, put the red on the middle post and go left and right with the black lead. Now, some of those posts will be open across them from the start, it's just the ones that do move the needle should move it steady and evenly, no hickups of any kind.
I use an analog meter because the drop/twitch can be very subtle. On a digital meter you could be watching the ohms climb,,, 1.0 1.2 1.3 1.4 ect.... (totally random numbers for the sake of demonstration BTW. Again, the steady climb is what's important.) and if the dropout occurs say between 1.3 and 1.4, it could simply appear and the display as the difference between the numbers clicking between .3 and .4. This is why we use an old school analog meter for this.
Think of a TPS like the volume control knob on old school stereo. Now imagine as you turn up the volume, you have a wonky place in the control knob. If your car stutters around 2500, then that would be like your volume knob stuttering at around 4.5.
So I changed the TPS and it made a huge difference. Still minor dead spots around 3k and 4.5k Could it be MAF? what's your thoughts?

Thanks
 

90sickfox

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It could be MAF related but usually they done cause that issue. That fuel pressure is high and will make the injectors act like they are bigger than they are. That will make them run richer than the car is expecting.

Do you have the factory FPR or is it aftermarket ?
 

7991LXnSHO

wanna catch the space herp
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32ish at idle with vacuum line on
42+ish at idle with vac line off and plugged
The pressure drop when you turn the key off is not really a concern,
When you rev it up a little the pressure should rise to 42-4ish and not fluctuate.
JMO and this is how my fuel pump readings were
I had 39-40 psi in mind with the line disconnected blocked, and varying with the line hooked up at idle. 10-12 extra psi sure will not help it run right. The aftermarket regulator I have is adjustable through the vac port. I think the stock ones are, too, but it’s been a long time since I had a stock one.
 
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Bree

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Jan 12, 2021
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Zanesville Ohio
Good to hear the TPS was a big help.
Something else I'd check that is often overlooked is a little something called the MAP sensor. Manifold Absolute Pressure. Should be high on the firewall, just passenger's side of center, a black box about 1 1/2in wide, and 3in tall. Should have a couple wires and a vacuum line coming out the bottom of it. May not be it, but it's worth a look anyway.
Couldn't hurt to take the EGR valve off and clean it out real good with carb and choke cleaner.
 

Dtambs39

Member
Feb 25, 2021
23
2
13
50
Dallas
It could be MAF related but usually they done cause that issue. That fuel pressure is high and will make the injectors act like they are bigger than they are. That will make them run richer than the car is expecting.

Do you have the factory FPR or is it aftermarket ?
its a stock replacement FPR.