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Throttle Position Sensor

SPSERG

NAXJA Forum User
Location
Massachusetts
I have tried all the local parts stores for a TPS. Knowbody has one or can get one. Tried Napa, autozone and all the local guys. Scared to death of what I will pay at the dealer, any ideas?
 
From your profile you have a Renix XJ. They used that system 87-90 on the 4.0 engine. It is a TPS with two connectors attached. One is for the engine computer and the other is for the transmission computer.

I got mine at rockauto, it was the best price I could find and Standard is a good brand. But with most autoparts onley a couple places make them and then are boxed for everyone.

Once you install the new TPS you need to calibrate it. There is a procecure where you use a digital multimeter (DMM). You measure off the connector used for the transmission computer. This method is better than nothing and will get you in the ball park.

I recommend you take the XJ to a shop that has the electrical test set and have them set the TPS. I purchased a Snap on MT2500 off ebay last fall to use on my 88 XJ. It the only aftermarket tool which will do TPS calibartion on our engines. The autoxray tool does not doe TPS calibration.

I recommend you get the TPS calibarted using the special tool. the DMM method does not take in voltage drop over the wire back to the computer. using the tool you will get the TPS so the computer has the right value.

I used my snap on tool on two friends GM cars. They both replaced their TPS and then used the DMM method. I hooked up my snap on test set and if ound they were both 0.20 volts too low. After we changed the setting the vehicles ran better. the 1985 Vette had a MUCH better idle, my cousin could not believe the difference. newer vehicles use a self calibrating TPS so no headaches like we live with.

Change it and get it professionally calibrated.
 
Its a different part number fot the manual trans. I dont know if thats the problem. Napa told me they would have it in one day, that was a week ago. They show 5 in the warehouse, but cant find any. Autozone told me the part was not available and the local small guys who use standard, said the same.
 
Well you are still not out of luck. The automatic transmission is just like the manual transmission TPS, the only difference is the connector for the automatic transmission. The connector for the engine computer is the same.

You can always buy the automatic TPS and install it. You then can take shrinkwrap and cover over the unused connector. Should serve you just fine.

That should be the MacGyver work around ...
 
That almost seems to good to be true. Are you sure about that?? Most of the auto parts stores refuse to take returns on electronic parts, so if I spent the $$ and it did not work... The funny thing about it, the TPS with the extra connector for auto trans is a buck cheaper than the manual TPS without!
 
Yes, I am sure the TPS will work. I am an engineer and know what engineers do to make life easier. You do not want to have a different connector on the throttle body which is dependent on which transmission is attached to the engine.

I was having problems finding a picture of the automatic trans TPS. Go to partsamerica.com and look up the TPS for your XJ. They have a picture of the TPS so you can verify the connector on your TPS is also present on the one in the picture.

Also I'd recommend you start a sensor replacement program. I changed every sensor which is used to run the engine. They degrade over time. I will say every time I changed a sensor the engine ran just a little bit better.

If you choose to do the sensor replacement program. I recommend you next change the Manifold abs pressure (MAP) sensor and then the inlet air temp sensor. When checking prices do not overlook the dealer, I purchased my stuff from the dealer or rockauto.com.

Other things to consider for the future - you have a choice of normal or high altitude. they cost the same at the dealer and with the high alt you get more advance. More advance is not a problem since you have knock sensor.
* crankshaft position sensor
* Idle air controller (IAC)
* Knock sensor
* Coolant temp sensor - this is a hard one, do it last or when changing coolant.
* Ignition coil and Ignition coil module
* engine computer - got a rebuilt one
* Distributor - the bushings wear and will retard your timing, also the cam shaft pos sensor, also known as the sync sensor, is in the ditributor. this sensor tells the injectors to shoot fuel

Also if you still the the metal fuel injectors you need to change them out. They are known for leaking at the seam between the metal and plastic portion. If you do this you should change the pressure regulator while you have it apart. Also you need to the the fuel line coupling repair kit at the dealer, you will need 2 of them and they run $15 each.

Hope that helps!
 
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Well, thank you so much for the help. I looked at the PartsAmerica web page and it sure looks like the right connector. Just the additional plug. I am going to run down to Napa and see if the can get the auto instead, since I already paid for the manual TPS.
 
If the price difference is only a buck then I'd not worry about getting that automatic TPS. I'd rather had the manual TPS if i was you BUT IF you could not get the manual TPS then you could make the automatic one work.

With the right TPS there now worry about water getting into the taped up connector.
 
martin said:
I recommend you take the XJ to a shop that has the electrical test set and have them set the TPS. I purchased a Snap on MT2500 off ebay last fall to use on my 88 XJ. It the only aftermarket tool which will do TPS calibration on our engines. The autoxray tool does not doe TPS calibration.

I recommend you get the TPS calibarted using the special tool. the DMM method does not take in voltage drop over the wire back to the computer. using the tool you will get the TPS so the computer has the right value.

Not to thread hijack, but I'm curious now, and looking on ebay... which cartridge and cable/adapter lets that scanner plug into our older XJ's? It almost looks like that strange black one shaped like a '[' would fit into the two diag connectors under the pressure bottle, but no way to be sure.

And as a more on-topic question, now that I think about it... theoretically if you measured the TPS voltage at the ECM end of the wire (under the dashboard) wouldn't you get a better measurement, if wire resistance between the TPS and ECM is what we're worried about here?
 
I may have been mistaken about the TPS... The TPS for a manual has a socket on it for the plug in. On the Auto, it has a short lead and connector to plug into the harness. I was looking on the All-Data site, and they look different. Maybe its a dealer item only after all
 
brtb, If you are asking about the Snap on MT2500 scanner you will have to make sure it comes with the JEEP-1 adaptor. It should be in any set you buy.

When I purchased mine I made sure the Data and diagnostic cartrages said Jeep on them. The older ones said GM-Ford-Chrysler. Starting around 94 issue dates you see ones that say GM-Ford-Chrysler-Jeep. Those are the only ones I'd consider if you want to buy one off of ebay.

The Jeep-1 connector to the diagnostic connectors, one of those pins provides "serial" data to the test set from either the engine computer or the transmission computer. There is no way to use the Jeep-1 connector and a mulitmeter to calibrate the TPS.

If you want to lay on your back and probe go right ahead. I am not sure if you will get the right pen and then who would monitor the display while the TPS is adjusted. I'd rather use the mulitmeter at the TPS method over the measures i at the computer which is located behind the cigar light on the dash board.

SPSERG, I'll double check my electrical troubleshooting manual for the TPS connector and find out if there is a different one for manual transmission. I still think the answer will be "no" cause of the logistics/engineering reasons I mentioned earlier.
 
SPSERG, I went home for lunch today and looked at my 88 XJ electrical troubleshooting manual. I looked at the wiring diagrams for 4.0 engine fuel injection system and the Automatic transmission system. There is no call out on the diagram saying the connector for fuel injection system TPS connector being different with different transmissions.

The 3 wire connector shown in your second picture looks like the one called out in the electrical troubleshooting manual and what is under the hood of my 88 XJ Pioneer AW4.

If you notice on the automatic transmission TPS picture you posted the two electrical connectors are not shown but in the manual transmission TPS picture the connector is shown.

I'd still try to get the manual trans TPS for your XJ since you don't have the support bracket for the TPS harness shown in the automatic TPS picture.

I'd bet a cold beverage that the length of the TPS harness on the engine side is the same for either transmission configuration. I have the connectors for my TPS laying on the intake manifold and can visualize in my mind how you could connect up the fuel injection harness to manual transmission TPS.

The automatic 4.0 engine is the only one I know that has two connectors on the TPS. Every other vehicle I have seen - 1988 Buick 3800 V-6, 1985 Corvette 350 LS-1 V8, etc - all have the single electrical connector on the TPS.

I still think either TPS will work for you but if the price was basically the same I'd go with the manual transmission TPS for your XJ.
 
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