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| Confusing TPS Problems | |
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| Tweet Topic Started: Apr 17 2011, 11:08 PM (3,479 Views) | |
| Wobblybob | Apr 17 2011, 11:08 PM Post #1 |
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Help! My '95 3/5 has been idling fast on an intermittent basis (becoming more frequent it seems). Fast idle is apparent by ear and by the fact that DFCO doesn't work much of the time when it should (observed on MPGuino). Although I had no tach, I suspect it was idling at about 1200 to 1500 when it misbehaved. Geo Glenn and mcmancusso suggested faulty or out-of-adjustment TPS. Read what I could find on the forum and used geoblues' procedure for checking TPS and found that rotating the TPS with an .012 feeler gauge at the throttle stop screw had no affect on the continuity of terminals A & B (the two nearest the firewall). Always open circuit. Assumed bad TPS. Bench tested and got same result: A & B always open. Pulled TPS from '94 XFi parts car and bench tested: A & B switched from open to closed as switch was rotated. Assumed it to be a good TPS. Meanwhile back at the ranch, I was also installing a "new" instrument panel with tach and without thinking about the absent TPS switch (they were both on the bench), started the car to check the tach. Started and idled about 1000 rpm, and gradually (30 to 45 seconds) increased to about 1500 rpm. That's when I saw a check engine light and remembered there was no TPS installed and shut it down. Installed the TPS from the '94 XFi, tested it for continuity and switching (with 0.012 and 0.035 feeler gauges) and set it up as geoblue instructed (0.012 feeler gauge, then 0.035 feeler gauge). Started to take it for a test drive, but when I started it, the idle went to almost 3000 rpm and stayed there. Pulled back into garage. That's when I discovered that there are only 3 wires on the harness: A, C & D. There is no B wire so the lack of an A/B signal on the original TPS means nothing. Retested original TPS on bench and found that if I checked terminals A & C, it performed as expected. Tested XFi TPS same way (terminals A & C) and found it did not switch as expected. Decided to reinstall original TPS and set it as instructed by geoblues, but checking terminals A & C instead of A & B. When I went to insert the .012 feeler gauge at the throttle stop screw, I discovered that the gap between the throttle and the stop was now about 3/16" and couldn't be reduced (it had been slighly more than .012" but much less than .035"). I manually opened and closed the throttle several times and found that the throttle is hitting a hard metallic stop. It appears to be the plunger which extends from the device on the back of the TBI (the IAC?). In any event, although I can reinstall the original TPS as I found it (I marked it), I cannot set it up as recommended by geoblues because the .012 feeler versus the .035 feeler gauge is meaningless with a full-time 3/16" gap. So, what is causing the 3/16" gap? And how do I restore the original .015" (or so) gap so I can set up the TPS? This my daily driver so any help would be greatly appreciated. Thanks in advance. |
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| Deleted User | Apr 17 2011, 11:16 PM Post #2 |
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Wobblybob, Send me a PM requesting pictures from the '95 FSM, and a link to this Topic, so I don't forget. I'd do it now, but the camera batteries are dead. '95 3 cyl. 5 speed, right? Geo Glenn |
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| mcmancuso | Apr 18 2011, 12:30 AM Post #3 |
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I thought the gap for closing the switch was 0.120 not .012... I could be wrong though... |
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| Wobblybob | Apr 18 2011, 12:50 AM Post #4 |
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Yeah, I thought I saw that too but I printed out geoblues' post and double checked the numbers. Also, when I started the gap was close to .012" and the idle was close to what it should have been. Now the gap is, maybe, .188" or so and the idle is at 3000 rpm. That makes me think the .012" is right. But, If I'm wrong I'd admit it in a second, especially if it leads to solving the problem. So fire away with any suggestions or corrections. I'll try anything! Thanks. |
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| Wobblybob | Apr 18 2011, 07:56 AM Post #5 |
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Geo Glenn has PM'd me 9 pages from the FSM and I'm studying as fast as I can. Thank you Glenn. In the meantime I think I'm going to try reinstalling the original TPS as it was when I started and see if I can get back to "normal". Once I get back where I was originally, hopefully the car will be driveable. From there I will try to adjust the TPS based on the continuity/discontinuity on terminals A & C. BTW mcmancuso, the feeler gauge you're to start with is .35mm, or about 0.014". The second one you use is .035" (.889mm). Maybe that's where the confusion comes in (seemslikely since I'm still confused as I type this!) |
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| Deleted User | Apr 18 2011, 09:49 AM Post #6 |
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Posting the pages - so we can all be on the same page! ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]()
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| Wobblybob | Apr 18 2011, 02:45 PM Post #7 |
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Well, I'm back on the road again but I'm not sure I'm much smarter! I reinstalled the original 4 terminal, 3 wire TPS and set it to the same position it was in when I started. Didn't even bother testing it to find the exact on-off point, just put it back where it had been before. Started the car and my newly installed tach (at least THAT works right) showed about 2000 rpm for a few seconds and then started slowing down and settled out at about 1400 rpm for maybe 10 to 15 seconds then gradually slowed down to about 1000 as things warmed up. I took it for a short ride and it seems to run fine. Biggest surprise was the DFCO seemed to work every time I tried it (a first). I stopped 3 times and it was idling just like it should. I didn't really have time check it out carefully yet, but I will. So what did I learn? - First, 94 and 95 TPS's and wiring harnesses are different. My '95 3/5 has a 3 wire harness feeding a four terminal receptacle but only connected to terminals A,C & D and the TPS's rheostat appears to be on terminals A & C. (A is nearest the firewall). '94's have a 4 wire harness connected to all 4 terminals on the TPS and the rheostat is on terminals A & B. Unfortunately, the plugs and receptacles are identical and interchangeable which adds to the confusion. - Always mark the angular position of your TPS before you try adjusting it. I did and it saved me. - I have a lot to learn about acronyms and the workings and the interdependence of the TPS, the ISC, the IAT, and the PCM. (throttle position sensor, idle speed control motor, inlet air temperature sensor and the power control, module)(phew!) - I changed something (?) in the course of this fiasco which seems to have fixed the intermittent high idle and the frequent no-DFCO problem. Who knows what? Cleaned up terminals by unplugging and replugging? Reinstalled the TPS slightly different and brought the idle down? Unintentionally "loosened" up or cleaned the rheostat windings in the TPS by manually rotating it on the bench? - We have some great guys on this forum who will go to a lot of trouble to help out other members without any thought of personal gain - thanks Glenn. Edited by Wobblybob, Apr 18 2011, 03:04 PM.
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| mwebb | Apr 18 2011, 10:43 PM Post #8 |
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FOG
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DFCO functions with the closed throttle switch on my 1996 G10 the closed throttle switch is on the IAC not the TPS to set TPS do NOT frak with feeler gauges , the ECM wants to see 1 volt at idle so ... at HOT idle , signal on TPS , center pin should be 1 volt , one of the other pins MUST be 5 volts and the other MUST be 0 volts with respect to battery negative if ground is above 50mv you will piss off MR ECM and MR ECM does not like that at all , anything could happen as a result but if TPS ground is high then so are the other grounds .... if you have runaway high idle verify that the hot water hoses in the throttle body are getting hot and NOT clogged internally if the hot water fast idle is high , closed throttle switch will never close , you will never have DFCO in warmer to hot weather , the negative effects of clogged hoses and bad thermostat are diminished Edited by mwebb, Apr 18 2011, 10:47 PM.
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| Wobblybob | Apr 19 2011, 05:20 AM Post #9 |
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Thanks mwebb. I was hoping you might see this. I took it for a 15 mile, multistop test drive yesterday (40 degrees outside) and it's not right. TPS was where it was originally (angular position) and idle kept creeping up as the trip progressed, and settled out around 1400 rpm. Also lost DFCO, as seen on the MPGuino. Took it back to the garage and finally made some T pins (aircraft safety wire) and set the TPS at 1.00 volts between terminals A & C (key on, engine off, no feeler gauge). I had to rotate the TPS about 1/8" clockwise from it's original location to get 1 volt. Test drive. Idle started at 1200 then dropped to slightly below 1000 before I even moved. Drove it about 2 miles. No DFCO! First stop, idle back up to 1400! Damn! Back to garage. Thought maybe I needed .014" feeler gauge while setting TPS so I reset it at 1.00 volt with the feeler gauge. Test drive. No change: no DFCO, 1400 idle. Wine time. 2 glasses. Went to bed. Saw your post this AM. First I'll check pin voltage to battery negative. (Don't know if my HF DMM can see 50mV or not?) if all looks good there I'll check the TBI hot water hoses. Then, who knows? Thanks. I'll report in. Edit: I'm also going to reset the TPS, only I'll be sure everything is HOT first. After reading your post (mwebb) I remembered that by the time I did my initial "T pin, no feeler gauge" setting, the engine had pretty much cooled down. After that didn't work, and the engine was hot, I reset the TPS (using T pins between A & C) with the engine hot and a 0.014" feeler gauge. I recall that the ISC motor plunger was tight against the throttle lever screw and I had to manually twist the throttle to insert the feeler gauge. No surprise there I guess but it confirms that the ISC Motor plunger was, in fact, holding the throttle open and creating the high idle. Edited by Wobblybob, Apr 19 2011, 07:11 AM.
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| Wobblybob | Apr 19 2011, 09:05 AM Post #10 |
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Update. First, ignore my comment in the "Edit" to my last post regarding the ISC Motor plunger being tight against the throttle lever screw. Incorrect. Dead wrong. The throttle lever was tight against the hard stop on the TBI - that's where you insert the .014 feeler gauge - not between the throttle lever and the ISC Motor plunger. In fact, since it was hard against the TBI hard stop, it would indicate that the ISC plunger was NOT holding it open. Exact opposite of what I said in my edit. Not sure what it means yet but wanted to clear it up. Started off this morning (40 degrees out) with a 4 mile test drive to warm things up. On cold startup engine idled nicely at 800 to 1000 rpm. Great! As I traveled down the road I let off the gas and pushed in the clutch occasionally to see where it idled. The warmer the engine got, the higher the idle got. At my 2 mile turnaround it was idling at 1600 rpm (no electrical load except wipers) with the car stopped. DFCO didn't work anywhere on test drive. I tried it several times, cold, hot didn't matter. Back into the garage. While it was still hot I reset the TPS to 1.00V A to C, no feeler gauge, key on, engine off. Then I checked voltages to battery negative. Terminal A = 5.2mV, terminal C = 1.0 V, terminal D = 4.98V. All good, right? Second test drive. Idle started at 1200 rpm with temp gauge about 1/4 scale. Down the road a ways when it had stabilized (at about 1/2 scale) idle had climbed to 1900 rpm. At 2 mile turnaround, initially idle was 1800 then slowed down (over 10 seconds or so) to 1500. Pulling back into garage, idle was about 1600. No DFCO anytime during drive. Next I'm going to check hose temperature to verify that the throttle body is getting proper heat but I have to read up to be sure which hoses I should be checking. I'll report in. Please feel free to offer comments in the meantime. Edited by Wobblybob, Apr 19 2011, 09:10 AM.
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| mwebb | Apr 19 2011, 10:24 PM Post #11 |
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FOG
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...." Next I'm going to check hose temperature to verify that the throttle body is getting proper heat but I have to read up to be sure which hoses I should be checking."..... they are small diameter hoses that connect to the intake manifold and throttle body, i would swag that they are around 8mm or 5/16" id rubber hoses , with moulded in bends , both should be hot about 180 to 200f when the engine is hot with temp gauge at 50% |
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| Bad Bent | Apr 20 2011, 10:07 PM Post #12 |
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Facetious Educated Donkey
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Click on this for a pic of the TB coolant hoses...
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| Deleted User | Apr 21 2011, 12:03 AM Post #13 |
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Getting it figured out, Wobblybob?
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| Wobblybob | Apr 21 2011, 09:55 AM Post #14 |
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Well............ where to start? Good news is that I'm back on the road in a reasonably well behaved car. Bad news is it's still not really right - it's just working OK. (This is long and boring so you might want to bail out now. Long story short: really read the FSM, assume nothing and ask for help when you're stumped). After my last post (4/19, 9:05AM) I drove the car locally with a 1500 idle and no DFCO. 4/19 afternoon Finally took the time to READ the FSM posted by Geo Glenn and the 1999 version my brother has and discoverd that mcmancusso was right about 3 days ago when he questioned the feeler gauge that's to be used setting the TPS. The FSM clearly states that the feeler gauge is to be 0.14" thick - over 1/8" thick! And their drawing shows a thick feeler gauge too. (duh!) At 9PM I tried resetting TPS using 0.14" feeler and 1.00V method. Test drive. TERRIBLE!! Cold idle 2000 rpm. After warmup idle started hunting, jumped to 2000 then over about 5 seconds dropped to 1600, jumped back up to 2000 and slowed to 1600 in 5 seconds, over and over and over, forever if I let it keep going. Back in the garage I could watch the plunger on the ISC pushing the throttle open and then letting off. I finally cried uncle and called Johnny Mullet at 9:30PM. We agreed that something (?) must be wrong with the ISC motor. I decided to unbolt it temporarily. (I told Johnny I'm not sure what's wrong, but right now it's not my friend). Test Drive. ISC unbolted, 1600 steady idle whole trip, DFCO worked fine. Back in garage. Reset TPS using mwebb's method: Hot, no feeler gauge, 1.00V. (ISC still unbolted) Test Drive. 1400 to 1600 steady idle, no DFCO. Back in garage, engine running, loosened TPS and rotated by had trying to lower idle. No effect whatsoever. Set back to original (4/17) mark and called it a night. 4/20 AM Drained cooling system, took TBI coolant hoses off (upper end only), blew compressed air thru both. Air and antifreeze came out radiator cap, petcock, and other hose, closed petcock and cap, blew into one hose, came out other one, reversed and same thing. Blew out TBI passage in both directions. Hoses were very clean and not "gummed up" in the least. When refilling cooling system had to run engine and hoses got nice and warm. This is not the problem. Test Drive (partially warmed up). (original TPS setting, ISC unbolted) 1100 rpm idle initially, climbed to 1400-1500 when engine fully warmed. DFCO only works in 3rd gear (No DFCO in 5th or 4th at 55 MPH). Suspect tach reading 10% high (3000 RPM at 55 mph), should be about 2700. 4/20 7PM Realized I had been setting TPS at 0.114, not 0.14 (will I ever get this right?) so I reset the TPS cold using the 0.14" gauge. (Thought maybe 0.026" difference was keeping DFCO from working consistently). Ended up being 1/16" or so CCW from the very original setting. Don't scold me mwebb for using the feeler gauge instead of doing it your way. I was a desperate man! Test Drive. 0.14", 1.00V, no ISC. DFCO better, 1400 indicated idle 4/20 8PM After resetting TPS, decided to reinstall ISC and see if it settles down. Installed it. Test Drive. Never made it out of garage! Idle seemd OK on start up but as soon as I touched the gas pedal, engine surged to 2500 and started cycling between 2500 and 1100. 4/20, 9:45 PM Called Johnny Mullet and arrange to go get his ISC motor. Unbolted mine and and drove to his place (26 miles). (1400 idle, DFCO worked most of time) As I kinda suspected, John couldn't resist poking around under the hood and here's what he discovered. 1. There are no obvious vacuum leaks. 2. Here it is, the "AHA!" moment: Someone has reset the idle stop screw on the TBI which, simply put, wouldn't allow the car to idle down. THAT has been the underlying problem the whole time but I was afraid to even think about touching it based on the precautions everywhere. John adjusted it with the lights and heater blower on and brought the idle down to 800-900 indicated (1000-1100 with them off). FINALLY! 3. We decided to install his ISC motor so all would be kosher and when we did it did the same thing as mine: rpm's surge to about 2000 then gradually back to about 1000, surge again and back to 1000, over and over and over. John's puzzled (and so am I, of course). So now I'm wondering what part of New York state mwebb lives in since I'm in PA, one of his neighboring states, if you get my drift. My bet is, if I could drive up there, he could put his scopes and/or meters on this thing (or maybe just lean his head on the hood, telepathic, you know) and explain whats going on and how to fix it. How about it, mwebb? In the meantime, thanks to GeoGlenn, mcmancusso, mwebb, bad bent, JM and everyone else for all your help. Great guys, all of you. Edited by Wobblybob, Apr 21 2011, 10:11 AM.
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| bogs | Apr 21 2011, 11:17 AM Post #15 |
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Duct tape heals all wounds
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That was quite a journey already ! |
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