Car surges at WOT & TPS only registers 75.7% at WOT. Why/help/thanks

V10SpeedLuvr

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For a while, my 96' RT/10 has had an issue at WOT. It drives fine at non-WOT, but as soon as you put the pedal in the floor, it starts surging. I've recently got serious about solving it (not many places in FL to go WOT, so this wasn't a top priority). One thing I've found is my TPS only registers 75.7% at WOT.


I replaced the TPS, same % shows up on my scanner. There is only a couple mm of adjustment on the TPS (it was 75.2% before the maxuimum adjustment I could make). I have a spare PCM, so I hooked it up, same #'s. I took off the LH intake tube and confirmed the butterfly was opening all the way. I resynched the throttle cables, no change. I then took the TPS off the car, but left it plugged up. If I actuate it with a flathead screwdriver, it registers 99.x%. So why is it dropping 23% when installed on the car?


Just for comparison sake, I scanned my DD and it registers 99.2% at WOT, so it's not a scanner issue.
 

Steve-Indy

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Is your throttle cable stretched?? Pedal stop problem?? I posted a solution to this on Gen I's MANY years ago.
 

V10SpeedLuvr

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I thought about those possibilities, but if I leave the TPS installed on the car and reach inside the t-body and manually open the butterfly all the way, it still only shows 75%. Its like it should be a lot more adjustment, but the highest I can get it was around 80% and in that position, the bolt holes were nowhere closing to lining up with the holes on the t-body assembly.

I'll try searching for your thread and check it out anyway, thanks for the suggestions.
 

daveg

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When you open the butterfly's are they completely horizontal? and not at a slight angle? What is the reading at idle position?
 

V10SpeedLuvr

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They looked completely horizontal, maybe a small angle, but not much. The part attached to the cable is all the way against the t-body bracket preventing it from opening any further when the butterfly's are all the way open.

Idle % was around 15%, IIRC. When I had it off the car, but still plugged up, I want to say it was around 8%.
 

daveg

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Sure its the right TPS? Did you match it up to your DD? Also, what is the WOT Voltage at?
 
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daveg

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75% may be right, you have to read your voltage. I thought you stated that you scanned your DD (Daily Driver) above. I have a 96 GTS and a manual, I can try looking up what the voltage should be at WOT.
 

V10SpeedLuvr

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Sure its the right TPS? Did you match it up to your DD? Also, what is the WOT Voltage at?

My scanner only shows %, no voltage. Sorry I wasn't clear, my DD isn't a Viper. I just wanted to see if the scanner would read my DD TPS at a much higher %+, to be sure it wasn't just my scanner showing bad info.

I'll work on getting a voltage reading. I have the 96' RT/10 manual, so I'll check it out on what voltage should be. Thanks for the help.
 

daveg

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Gotcha... 75% could be right (I know it doesn't sound it but it might be) Need to read voltage with meter.
 

speedracervr4

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I take it you have manually moved the buttflies to see what the tps reads with the throttle cable not hooked up. This would let you know if it's a cable binding/pedal issue.
 

V10SpeedLuvr

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I take it you have manually moved the buttflies to see what the tps reads with the throttle cable not hooked up. This would let you know if it's a cable binding/pedal issue.

I left the cable hooked up, but manually open the butterflies as far as they would go. That's the 75% reading. If I take the TPS off the car but leave it hooked up and turn it with a flathead screwdriver, the scanner reads 99.x%.

If the 75% reading is correct, I'm back at square one on why the car surges at WOT, but fine at say 70-80% throttle.
 

daveg

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He did state above butterfly's were horizontal at WOT. I suspect 75% might be correct but wont know until voltage reading...
 

daveg

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I left the cable hooked up, but manually open the butterflies as far as they would go. That's the 75% reading. If I take the TPS off the car but leave it hooked up and turn it with a flathead screwdriver, the scanner reads 99.x%.

If the 75% reading is correct, I'm back at square one on why the car surges at WOT, but fine at say 70-80% throttle.
Still may be your problem if voltage fluctuates at WOT.. Leave it WOT for a bit to see if voltage changes. May want to use analog meter and not digital..
 

ViperJohn

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I remember reading my TPS sensor percentage a few years back. Idle was around 16% and full throttle was in 70's. I thought it was odd, however, if you ever re-install throttle bodies, you have to spin TPS sensor a bit to line up TPS hook up. I don't believe the TPS is ever fully engaged in either the open or closed position. The voltage is what the PCM is looking for, however, if you hold pedal steady and percent remains stable, your sensor should still be outputting steady voltage.

As far as surging goes, I assume you have checked the usual suspects, such as spark plugs, cables? Another culprit could be the fuel pump. You can buy a fuel pressure gauge for about $20. Remove your cowl and connect the fuel pressure gauge to the schraeder valve on the passenger fuel rail. Run the line along cowl and tape onto front windshield. Removing the cowl will give you space to run line while hood is closed. Drive the car. I can't remember correct fuel pressure reading off the top of my head, it's either 28 or 58? Sorry, it's been a few years since I did it. Essentially what you should be looking for is steady fuel pressure. If fuel pressure drops off during WOT, your are having a fuel delivery problem. Could be the fuel pump and/or fuel filter.

Good luck resolving. PM me and I can call if you have any questions.
 

Dom426h

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Three more Q's:
-Is your scanner capable of looking at the real time graph of the O2 sensors?
-Is your problem constant or intermittent? If intermittent, how so?
-Define 'surges' ... any more description/details?
 

Jack B

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That is is an absolute calculation, most cars will read close to 80% at WOT.
 

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