rcp5041

Hi all,

Long time lurker first time poster. I bought an 88 4runner about a year and a half ago as a weekend warrior/winter vehicle since my vw's didn't go so well in the snow. I developed a coolant leak from a blown head gasket and decided to tackle it myself.

It is currently all back together but it does not seem to want to go anywhere. I set the timing to 5 deg BTDC while short circuiting the two connectors and while they are jumped the truck seems to start right up. Once they jumper is removed the truck does not want to start and once it does there is no power. It does not rev well and backfires through the intake.

At first I thought I had the timing chain off somehow so I took the valve cover off and confirmed the cam was at TDC when the crank was and reinstalled the distributor.

I have since checked the tps to see if it was adjusted correctly and with no space between the lever and throttle stop screw the VTA to E2 reads 2.92 kOhms and at WOT reads 4.75 kOhms. Also no matter which position I move the throttle to the IDL to E2 doesn't read anything on the meter. This would lead me to believe my TPS is bad. Before I go and buy a TPS I was wondering if I could get any input with the forum as to if it sounds like i'm heading down the right path. Any help would be greatly appreciated.

Thanks,

Ryan

Co_94_PU

iTrader: (-1)

Source a resistor of the appropriate rateing, eg whatever the idl-e2 is supposed to read when closed, and jam it into the harness side of the plug. Note you can't drive around like that but if the idle suddenly works you know.

I don't recall those test specs offhand for the others so you'll need to check em yer self.

rcp5041

If I can source one I'll give it a shot. I'm thinking of just going ahead and ordering the tps since the first test with no adjustment seemed to fail so miserably. Already ordered the allen head screws off of 4crawler to help making adjusting easier. Hopefully this solves the problem so I can get it back on the road.

cman1

iTrader: (1)

check your timing,then check it again.

scope103

No. It's not possible to have a meter that "doesn't read anything." It could read 0.00 ohms or infinite ohms (open) or 213.6 milliamps, but it can't display "nothing."

IDL-E2 is just a switch that is closed at idle, open otherwise. You're trying to read a switch, and you do it with the resistance scale. It "should" read 0.00 ohms when at idle, and "infinite" when it's open "a little" (defined as 0.80mm or more http://personal.utulsa.edu/~nathan-b...93throttle.pdf . But unless you have a super-conducting TPS, you're never going to get 0.00 ohms. So they make it easy for you; if 2.3kohms or less at idle, and more than that off-idle, that's close enough.

Testing the TPS while installed is a PITA. If you're really thinking of replacing it, you can remove it and just see if the switch works at all. If it does, then it's good, and you should use it. Then it's only a matter of adjusting it so it switches when the throttle is open "a little."

Don't do that; that resistor won't do you any good. The resistance isn't what matters; it's the the switching between idle and not-idle that's important.

Good luck!

rcp5041

Correct, I should have said it read 0.00 ohms.

PITA for sure. I only get a chance to work on it during the weekends so I'll take it off Saturday to make it a little easier to test.

I'll keep you posted. Thanks for the help.

Co_94_PU

iTrader: (-1)

The purpose of the resistor is to prevent a dead short, I'm not sure what the circuit looks like in the computer. If you can find the picture of the internals, or have a spare you'll notice it's actually a conductive strip not a reed-switch. What this does is verifies the wiring. It's not a hillbilliy fix you can't drive around like that, it's just a test.

regarding TPS adjustments.
You'll want a set of meter leads with clips of some form, Napa has aligator clips for 1.40 a pair, you'll need to pinch the ends closed a little to get a probe to stick hands free. Just run the probe wires between the two keep them from touching and you don't need the more expensive type with boots. Also make sure you're loosening both screws/bolts so it fully/correctly rotates. There is no reason to remove the throttle body to adjust the tps. You can replace screws with hex bolts or allen screws if you can't get a screwdriver to the stock screws.

snobdds

Yea, not a good idea. Like scope said, it's a switch...not any type of circuit.

snobdds

I also agree it is probably a timing issue. The timing needs to be set at 5* BTDC on the Compression stroke. You may have set it at 5* BTDC on the exhaust stroke.

Co_94_PU

iTrader: (-1)

Not to be argumentative but with all due respect, you are wrong sir. It is most definately a printed/silkscreened conductive strip not a reed switch.



*EDIT* (PB being non co-operative. that photo is "http://photobucket.com/albums/s153/Jameespics/85%20Toyota/DSCN9702.jpg", clicking open in new window/tab works album is private so I can't snag the "proper" link)
The reason it is a conductive/resistive strip is for the computer to calculate the position so it can null out the throttle position reading, other wise it'd just be a copper strip and function like a normal reed switch. I'm not saying it's not performing a switching function, I'm just saying it has an Ohm value for a reason.

You both seem to be ignoring the fact it is a test not a solution.



Now to be helpfull here is a possible cause for the TPS to not seem adjustable. Did you replace it recently? Did you compare the old one to the new one? There are some floating around out there that were assembled 90 degrees off, like in the picture above.

rcp5041

I got a chance to dive into the tps today. Took the throttle body off completely and bought a new one tps. Checked to make sure they were similar before I installed the new one and then adjusted the sensor per 4crawler directions. I then confirmed my timing was at 5 deg BTDC with the jumper installed. The truck instantly seemed to be running more smooth than before. Removed the jumper and it rev'd with no hiccups or backfiring with excellent throttle response!

I took it for a spin up and down the street and it seems to be running much better than before. In my 8 or so years messing with cars I've never had a tps go bad on me so I'm not sure if this was a gradual decline and it just bit the dust or if they go all of the sudden sort of like a fuel pump.

I did notice that when I applied the brakes that the idle would dip and then surge leading me to believe that there is a vacuum issue I need to address, but I was done for the day so If I get some time tomorrow I'll try to take a look at it. I also need to go buy a cheap tach so I can adjust the idle and set the timing more accurately. Seems to be idling a little high from just listening to it.

Thanks for all the insight. I'll report back when I figure out the rpm surge. Glad to have it running decent again and can't wait to get it inspected and back on weekend trail duty.

Co_94_PU

iTrader: (-1)

Could you tear that "busted" TPS's cover off and post a photo of the board, preferably an upclose shot so we can see where it wore out. Thanks in advance

For the dipping idle surge did you recheck the idle setting after the timing was corrected. It's a bit of a cyclical loop. Set idle adjust timing recheck idle and timing if you had to adjust the idle in the recheck.

for a rising idle surge it could be a leak in the booster diaphram, should be instructions inthe manual.

Er helps if I read the whole post and remebered it. yeah tach the idle and you'll probably be all set. From memory it's about 1+1/4 turns from where the fuel cut rpm dip starts to occur for the hillbilly idle adjustments.

P.S.*edit* if you do it carefully you might just need to clean the wiper contacts and you'll have a spare handy.

rcp5041

So i didn't get to the yota today (high of 25 with 20 mph gusts, no thanks) but I did get a chance to tear apart the old tps. It looks ok to me on the inside, although it seems to have quite a lot of resistance when you try to spin it. I can't recall if the new one would spin back to the original position after you let go or not, but maybe this had something to do with it.

Co_94_PU

iTrader: (-1)

yeah that spring might of been your whole problem, bound up from crud or just weak. The board looks pretty good, maybe some damage in the middle or it's just a reflection.

The right side is the Throttle angle. note the line of material transfered into the bare copper area, this is from build up on the wiper and caused poor contact.

In the 2nd photo there should be a nice glare coming off off the contact points of each wiper. Gently file or wipe these off till they are shiney like a new penny and lightly bend them upwards to ensure good contact, then wipe the circuit board down with some IPA, tv tuner or other electronic cleaner, and reseal and assemble to refurb.

If the spring is completely wore out there isn't much you can do, if you remove and replace the shaft(easier said than done, drill custom ground bolt or oval shaft. ect..) you would try to respring it by over extending it backwards(CCW).

If it's just binding you can lube up the spring side. Just a smidch of liquid lube(wd40/pb blaster,other liquid rated for engine bay use) applied to the shaft via tube thru the endent/cutout on the circuit board side.

Anyways thats TPS clean and refurbish 101. Thanks for the picture.

Wind sucks gets me all the time out here on the high plains

snobdds

I still stand by my origional statement. It's a switch, not any type of circuit. Putting a reistor in line anywhere is not a good idea.