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  #1  
Old February 21st, 2004, 09:21
gator_grabber gator_grabber is offline
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1988 Renix TPS readings

I've had an intermittent problem starting my Jeep after it has run for an hour or so. It will fire, run rough then die. If you give it a few minutes, it normally restarts without issues. The CPS is new and the fuel pump tests out fine. These are the readings that I'm getting from my TPS (1988 auto) with the throttle closed:

4.9 volts in
.67 volts out

This doesn't seem correct, but then again I'm running on a total lack of sleep.

Any thoughts?? Thanks.
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Old February 21st, 2004, 17:48
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martin martin is offline
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What I recall you take your voltage readings off the square plug not the flat plug. I never understood why you adjusted using the transmission connector but that the way it works.

There are 3 terminals used on the connector:
A - 5 volt supply
B - value for computer
D - Ground

The measurement between A and D should be 5 volts, think mine was more like 4.5 volts. You will use 4.9 volts

Then measure between B and D and it should be 83% of the 5 volt value when the trottle is closed. So for you it should be .83 x 4.9 = 4.07 volts.

If you do this you will be in the ball park. I changed my TPS and used this method then took it into the dealer for a problem and the tech told me "your TPS was out of adjustment so I set it back for you."

If you know someone with the Snap On MT2500 they can set it just like the dealer mechanic. I purchased one off ebay and it very cool to read engine and transmission computers values.

The multimeter method it better than nothing but if you can find a mechanic to hook up that snap on tool or have the dealer set it for you.

Measure like I wrote up and you will be doing better.
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  #3  
Old February 21st, 2004, 20:32
gator_grabber gator_grabber is offline
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This is a big help, thank you!
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Old February 22nd, 2004, 02:09
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Wiley Coyote Wiley Coyote is offline
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Martin, Since you seem to be knowledgeable about TPS maybe you could answer a question. I have a ’91 4.0l Auto and I’m trying to adjust my TPS. On mine there is NO provision for adjustment, the two bolts fit tightly in the TPS and it can’t be turned in the housing (throttle body). I’ve looked at a couple of pictures of other TPS on line and there appears to be a bolt in the center of them that you can loosen to rotate it slightly. Is that how you are supposed to adjust them? If so, it looks like I need to buy a new TPS with the center bolt.
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Old February 22nd, 2004, 08:46
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Coyote, I own an 88 XJ and seems like I have fixed most everything on it. Thanks for the compliment. I really have no knowledge to speak of on the 91 and later ignition system. If you hae a self adjusting TPS then install it and go for a drive, it should be calibrated after one drive.

Wish i could tell you more.. prehaps someone else on here can give you more info.
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Old February 22nd, 2004, 08:48
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Matthew Currie Matthew Currie is offline
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Quote:
Originally Posted by Wiley Coyote
Martin, Since you seem to be knowledgeable about TPS maybe you could answer a question. I have a ’91 4.0l Auto and I’m trying to adjust my TPS. On mine there is NO provision for adjustment, the two bolts fit tightly in the TPS and it can’t be turned in the housing (throttle body). I’ve looked at a couple of pictures of other TPS on line and there appears to be a bolt in the center of them that you can loosen to rotate it slightly. Is that how you are supposed to adjust them? If so, it looks like I need to buy a new TPS with the center bolt.
You do not adjust the 91-up TPS. The computer handles it. The system is quite different, so no voltage/resistance etc. specs for the Renix system are applicable.
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Old February 22nd, 2004, 11:41
BrokenXJ BrokenXJ is offline
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You may want to check your fuel-pump ballast resistor on the left front fender. To test it, just by pass the resistor. When this resistor goes, the XJ will start right up and then die.
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Old February 23rd, 2004, 01:57
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Wiley Coyote Wiley Coyote is offline
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Re: 1988 Renix TPS readings

Martin and Mathew, Thanks for the info guys. I swapped out my TPS with a new one and it solved my problems. It cranks right up and the transmission up shifts like it is supposed to now. You are right, I did have a “self adjusting” TPS. Interestingly enough when I tested the old TPS it was out of parameters (volts too high at idle) and the XJ wouldn’t start/shift correctly. I went ahead and tested the new TPS since I had the leads already hooked up and it was with in specs with no adjustments. It works like a champ now. BTW the ecu never threw a code for the TPS. It showed a 12 (bat. Disconnect), 17 speed sensor (readjusted and fixed it), and a 15 (engine too cold – I put in a 165 degree thermostat). Nothing about a TPS. It just up and died with no codes or warning. Is that normal?
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Old February 23rd, 2004, 07:29
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glfredrick glfredrick is offline
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Re: 1988 Renix TPS readings

I also need some help, but can't post a new thread yet as I am just signing up as a new user...

I have the I-4 engine which we swapped out for an old bad one, and now the trottle body just keeps on spraying gas into the engine.

Anyone have this problem?

If I disconnect the two-wire plug that goes into the top of the fuel injector, the engine will idle correctly, but not rev up, as it gets no signal to the injector. As soon asn the wires are re-connected it goes back into full spray mode and everything dies.

I really need ideas - and, by the way, I have tried both fuel injectors (from the old motor and from the new) and it does the same with both. This will very quickly fill the oil pan with unburned fuel (hence the new motor!).
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  #10  
Old February 23rd, 2004, 07:36
gator_grabber gator_grabber is offline
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Re: 1988 Renix TPS readings

The ballast resistor...Hmmmm. That one just slipped right past me. Let me get it hot and see if that's the culprit. Beware of the obvious!
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  #11  
Old February 23rd, 2004, 11:39
gator_grabber gator_grabber is offline
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Re: 1988 Renix TPS readings

Well, the engine gets hot and the ballast resistor gives up the ghost. Problem solved!

Now, where's a good place to buy a new one? Is it the same unit Mopar used on all of the old ignition systems?

Last edited by gator_grabber; February 23rd, 2004 at 12:17.
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  #12  
Old February 23rd, 2004, 19:54
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: 1988 Renix TPS readings

Any auto parts store should have them, and yes, they're the same type as Chrysler used on their coil circuits. If I remember correctly, they're about 1.2 ohms.
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Old February 23rd, 2004, 20:12
gator_grabber gator_grabber is offline
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Re: 1988 Renix TPS readings

The factory unit is "cast" as a 1.1 unit. The parts stores all had multiple resistors to choose from, but none at 1.1. For the time being I got one that's .78 when cold, 1.7 hot. It seems to work just fine, but I'd like to be certain that it will work long term. Any thoughts?
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Old February 24th, 2004, 07:26
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: 1988 Renix TPS readings

Gator, as you know, resistance varies with temperature. Electrical system values aren't absolute, and they'll change from a cold start to normal running temps. The resistor you chose should work very well. Be sure that no wiring touches it, because resistors normally run VERY hot.
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  #15  
Old February 24th, 2004, 10:04
gator_grabber gator_grabber is offline
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Re: 1988 Renix TPS readings

Since the parts store didn't have exactly what I wanted, I picked the resistor using SWAG...Scientific Wild Ass Guess. It seems to be working just fine. I'll report back if that changes.
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