Throttle Position Sensor Readings

[Tractor Dan]

Back probed the tps sensor today. Followed the article and the wiring diagram for my truck. Here is where things got interesting. With the throttle fully closed, i verified by looking at the butterfly. My meter was reading 4.16V fully closed. As i depressed the throttle linkage out at the engine it went down to .5 volts or so floated between .51 to .53 volts. From what i understand it should be the exact opposite of this. Also i checked the signal wire by back probing that and grounding my meter to the block and got signal voltage of 5v.

Background on the vehicle. 94 Ranger 3.0L. Engine was recently swapped in from a yard so who knows what the sensor has been exposed to. I want to investigate all options before throwing a $50+ sensor. I don't think it's wiring as i'm having no other issues with anything else. I'm going to look at wiring diagrams to see what else may share a common power or ground.

 

[kimcrwbr1]

http://www.youtube.com/watch?v=lJEGigONelc
Maybe this will help?

 

[Tractor Dan]

That did help. I also traced the wire colors on the schematic and made sure i knew what color went to what.

I tested the resistance as shown in the video. My meter isn't auto ranging. I set it to the 200 Ohms scale and got nothing. Just a 1 . Then i moved it to the 2000 ohm scale and it read 1.2 ohms. I'm going to test this again with another meter and i'm also going to get different pins. The pins i was using today were made in a pinch. I took the spring out of an ink pen and stretched it and straightened it to make pins. Once i get those and retest i'll post back on here. It drives fine. I did once get a TPS code but once we took the slack from the throttle cable and cleared it the code didn't come back.

 

[RonD]

The voltage was testing in reverse, 5 volts is the base voltage, so 4.16 would be .84v when throttle was closed, so that is fine.
.51 at WOT would be 4.49v which is fine for Wide Open Throttle.

Spec is .6 to .9 closed, 4.4 to 4.8 open fully

This is one of the "learned" parameters for the computer, so like horse shoes close counts

Issue with TPS is when voltage jumps around as you open or close it, so a dead spot in the variable resistor.

 

[kimcrwbr1]

Check the connector good on both sides clean good with electrical cleaner and use dielectric grease to put back together. Then with a small jewelers screwdriver make sure the pins are pushed full in on both sides. You can just use straightened paper clip to backprobe a connector. You can test the senser by itself with just the ohm meter from the power in terminal put one lead on it and then check the other two, the resistance should change high to low and low to high on the other as you open the throttle if you see anything other than a nice smooth change in the resistance the TPS is likely bad. A analog VOM (needle sweep) are good for testing a pot or variable resistor.

 

[Tractor Dan]

Never knew a TPS could test in reverse. First one i ever had do it to me. The values do make sense now i was just thrown off because of what i thought it should be reading. The voltage went up and came back down smoothly when i could get it to read. I was just checking it since i have been having idle and revving issues. I'm pretty sure it's a vacuum leak somewhere i just haven't found yet but thought maybe i would get lucky and it would be a TPS going haywire.

As for cleaning the connectors i'm assuming something like MAF sensor cleaner would work or is that too harsh? I was just thinking it may work. If not i'll buy some contact cleaner Friday. Looking at it, the pins don't look too bad but there is some dirt in the connectors.

 

[RonD]

MAF cleaner will be fine on electrical connectors.

For idle and reving issues, warm up engine and then unplug the IAC valve, idle should drop to about 500rpms or engine may stall, either is fine, it means no vacuum leak.
If engine RPMs are higher than 500rpms with IAC unplugged then most likely cause is a vacuum leak.
Since there are only a few vacuum hoses I would unhook them one at a time and put your finger over the intake hole with engine idling and IAC valve unplugged.
If idle drops to 500rpms or engine stalls you found the leaking vacuum system.

 

[Tractor Dan]

I'll give that a try. It only does it when the clutch pedal is pressed in and even then doesn't always do it. It was really bad before i had new valve guide seals put on. I figure this is gonna be like my 97 Ranger was drive it for a year to get all the bugs out of the thing.

 

[kimcrwbr1]

Have you checked the timing chain? turn the crank by hand clockwise to TDC Pull the distributor cap and watch the rotor as you turn the crank counterclockwise until the rotor moves. The crank should only move a couple degrees before the rotor turns.

 

[Tractor Dan]

Haven't checked that. I can give it a check. To check for TDC what's the best way? Most i ever done involving timing was when i was about 7 or 8 and dad was trying to do a timing belt on a Volvo 240 DL. Needless to say i was told to stay out of the way. Which is probably for the better he hated that car after that.

 

[Tractor Dan]

Ok. Started pulling vacuum lines one by one. Only one i didn't pull was the one going to the brake booster but i figured if that vacuum system had a leak i would notice it. Anyways when i pulled the line going from the distribution hub at the back of the intake to the fuel pressure regulator the rpm's went up. All the other lines either made the truck almost stall or there was a dip in rpm's. I think the only reason it didn't stall was the IAC was still plugged in.

So now that i think i have isolated the circuit what would be next to check? I would assume fuel pressure or to see if the fuel pressure regulator is functioning correctly by using a vacuum gauge and pump to apply vacuum? Also the line on there is the plastic vacuum line and i'm probably gonna replace that with hose if i can. Also i noticed running with the AC on today there was a bit of a drag on the engine. Not much but i don't know if that's normal for a ranger seeing as my 97's never worked. I'm still going to investigate the timing as well. Figure it can't hurt to investigate all options.

 

[RonD]

If possible connect vacuum hose to the FPR and suck on it(my kind of vacuum pump) if it holds a vacuum it should be fine, if it taste like fuel replace FPR.

Yes, AC on will lower the engine power

 

[Tractor Dan]

Tested the FPR. It tested fine except haven't done the vacuum gauge portion. Dad had a fit that i gasp spent $25 on a pressure testing kit and teflon tape rated for fuel. At times i want to remind him he should be thankful i'm not out using his money to buy drugs and with any luck i'll have a job next week.

5-24-2014 11:27pm

So. Got to investigating more. Started pulling spark plugs just for the heck of it. Neighbor told me to clean them and pop them back in. 2 were oil fouled. It's the 2 middle cylinders on each back. Well as i'm cleaning them found one was cracked at the center electrode. So new plugs are going in tomorrow. Hoping between that and some more seafoam i can get it running pretty good. I started noticing the last couple days it was fighting me to get up to speed and this spark plug issue makes sense if that electrode was cracked. So i'll keep yall updated. Thanks for the help so far. Slowly but surely this pain in the neck will run right. Or i'll blow it up one of the two. Hopefully the first and not the last.