Where does the Throttle Position Sensor input voltage come from?
I replaced the TPS 2 years ago and calibrated the OUT divided by the IN @ 83%, and it worked well until recently.
My current TPS readings are IN = 7.81 vdc, and OUT = 5.65 vdc.
I am suspecting my problems are centered in the origin of the voltage being supplied too high to the TPS and not the TPS itself.
Any advice is welcomed, thanks.
The factory manual for the Renix system (same as my '88 Commanche) says that the reference voltage should be 5.0 volts supplied by the computer but yours may be running slightly differently. My adjustment procedure (from the manual) is .86 volts ouput with the throttle at dead idle to 4.95 at WOT. If it is the 5.0 reference, you'll also find that the MAP sensor supply is high. If that's the case, good luck finding another computer! As I recall, the Rennix system was only used in 87 and 88 - maybe a few of early the 89's had it butthe 90's on used the MOPAR unit. That had totally different sensors and was set up for the HO engine with different intake manifolds and headers along with a reworked head. If the engine runs OK beyond the idle/WOT performance, you might be able to repair the voltage reference inside the computer but that's chancy - I've never gotten the schematics for that beast.
The ECU supplies both voltage and ground to the sensors.
There are two splices in the sensor ground circuit that have been very troublesome on the early (87 and early 88) 4.0L XJ/MJ. They used a bulkhead connector on the firewall that connected the engine harness to the injector harness. The splices are within about a foot of that connector, one on each side. They are crimped and duct taped inside the harness.
In the engine harness, there is a 3 into 1 splice. The single wire goes through the bulkhead connector, then a 1 into 3 splice in the injector harness. The circuit is brown with white tracer.
You can manipulate the harnesses in the area of the splices and watch the TPS voltage go nuts with a scan tool. I've never seen a physical problem with the splices (no broken wires, corrosion or high resistance), so it appears to be the way they routed the wires in the harness. Maybe too close to, or not protected well enough, from other current carrying wires. Whatever it is, you can open the harnesses and pull the splices out, isolating them from the harness and the problem goes away.
Since the bulkhead connector can be problematic also, I'd suggest bypassing it altogether. Just solder the 3 wires in the engine harness to the 3 in the injector harness. The splices are close enough to each other that it's easy to do. Tape it up and it looks good and no more problems.
Bill Hughes, Will, & Bllsht,
Thank each of you for responding.
When I posted the message, I decided to jump into the jeep and go purchase a new TPS as a last ditch effort when I considered the other possible costs.
My initial symptoms started ALL at once, back in May this year. While driving on the interstate, the transmission when out (save 1st gear & some second). Low fluid. So I immediately added enough fluid to get home.
The transmission wouldn't work properly and also started having engine idle problems (cold start kills, and also at running temperature having very high idles).
I dropped the pan, changed the screen, cleaned the magnet (slight haze covering it, no shavings), and the bottom of the pan was absolutely free of debris. The fluid smelled new and clear (zero burn scent). I put on a new screen and replaced the fluid, adding some lucas as a kicker.
I brought it into several shops and they would only tell me "oh, about two thousand dollars", but yet I'd hit a bump and I'd have 4 gears back up shifting and down shifting normally as if I never had a problem (but the idle problem prevailed).
Each time the transmission would randomly go ignorant, I'd checked the TPS. Each time it reported in @ 83ish% --until September. Once I replaced the TPS and calibrated, the idle issue when away -- and so did the transmission issue (save one). I did not get overdrive back. It's been a month, and I am at another dead end on what direction I should take.
I do not know if I damaged the 4th gear/overdrive planetary when I ran low on fluid (temperature wise) back in May, or if I have a pending overdrive electronic issue? MT2500 didn't shed any usable clues.
Based upon each of your previous postings with advise, I am going to break open & look into the wiring harness and also disconnect at the bulkhead to check the contacts this weekend.
Do you think my neutral safety switch is over due at 270k miles?
--Percentage wise? Aisin Warner 30-40LE.
Any Suggestions? Thanks, Ken
Will H>
At 276k on the clock, the whole power train is tired and the tranny has all sorts of worn parts, so I pass on that. For the idle, just unplug the TPS (both of them) and clean the plug contacts with contact cleaner.
When you put a scan tool on it, what DTCs do you get?
It's an '87, not '97. There is no scan tool to pull DTCs.
PeterD, I do not own a mt2500, but I found someone who had one. We were not able to get any specific codes from the ecu or the tcu, but all of the basic reporting features illustrated nominal/pass results. I heard it said that a DRB II would do nicely but no shop in the city has one. I have the Renix ECU made by Bendix (replaced with a new one 2 years ago).
What do you th> On Tue, 27 Oct 2009 09:39:55 -0600, snipped-for-privacy@earthlink.net wrote: >
Some ECU/TCUs will inhibit overdrive if there are codes, but that doesn't seem to be the problem. I'm not sure what's up at this stage.
FYI The Bendix Jeep Tester will get you those codes on an '87 and on my '88. I have the manual with all of the codes. I sent those codes to the Renix group on Yahoo after scanning them
Or, you can cycle the key OFF/ON five times and the Check light will blink the codes.
Not on the Renix system AFAIK. I think the 1991-1995 "Chrysler" OBD-I might have the blinking system. ;-)
The Renix ECU doesn't store DTCs. The tester you refer to (MS 1700) will guide you through a self test (key on, key off, step on accelerator, etc) and look for the proper response. If it doesn't see what it expects, it'll give you a code to look up a diagnostic procedure. Useful if you have a dead sensor, but no help if your problem is intermittent or a sensor that's just slightly off. The most useful thing is the serial data readout which lets you see sensor values in real time, but only one sensor at a time.
This tool was replaced by the Jeep/Eagle adapter used with the DRBII.
Since 10/2009, just wanted to follow up and update on the TPS issue.
I was sure my transmission was an electrical issue, and not a mechanical one. The TPS seemed to be a part of that premise. In the summer 0f 2010, after driving without overdrive for a year, I pulled into a sleeply little town in Mississippi (Pascagoula) and a home grown auto repair shop. Ole boy said his modis scanner said my brake was depresssed. --- Overdrive solved by replacing a burnt wire under dash near pedals. Just saved $2,300 for what 10 authorized mechanics wanted to charge.
Well, it's winter time again and my jeep is following it's attitude as in the past 5 winters. Cold temperature (35 to 45 degrees) it reeves over 3500 rpms the first time starting it in the morning. I have to shut off, and restart no less than 4 times before the reeving of the engine subsides. Any suggestions? EGR? vacuum? relay?
Your input has been and is appreciated, Ken
My wife showed me how to fix that on a 4.0L I6: KEEP YOUR FOOT OFF THE GAS.
More specifically, the old MJ (Renix system) does this race thing on cool starts ("cold" around here is generally single digits, +-, and with those the darned thing starts fine). At those intermediate temps, it will race as you describe under two conditions: If I give it ANY gas while starting and (oddly enough) if I pull into the drive in 2nd or 3rd then turn the engine off without letting it idle for a second or two. The second one there acts like a restart after stalling the engine taking off from a stop and backs off pretty quick but I can't figure why it "remembers" a stall overnight.
Two things helped the first of the above two: 1. clean the TPS lug really well and 2. get some contact cleaner into the TPS itself then work it back and forth to get the corrosion off.
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