RMVR53 Posted July 8, 2008 Share Posted July 8, 2008 I'm so sick and tired of this.... In my on-going pursuit to find the cure for my firing problems, I have replaced half the car...ok that sounds stupid but heres where I'm at.... New: plugs, wires, cap, rotor, CAS (yes I finally bought one...and it didn't fix my problem which REALLY pisses me off) fuel and air filters (ok..I was throwing parts at it early on)... cleaning/etc: removed all ground wires and cleaned at contact; removed all connections/plugs and cleaned contacts (under the hood for both); heres where I'm at: once the car warms up, the tach will bounce wildly and 99.9% of the time while under load/acceleration will miss and literally quit. Get your foot out of the gas and tach comes back and miss-fire quits. Get it going fast enough when this happens and under deceleration everything is fine...its just under throttle. Can the TPS switch do this kind of electrical crap with the tach ? If that wasn't going on I'd be looking at the TPS for sure but right now I'm at a loss... as a precurser - this is all after a 10 month tinker rebuild to replace a cracked head...ran fine prior to teardown. thanks Bill Link to comment Share on other sites More sharing options...
idosubaru Posted July 8, 2008 Share Posted July 8, 2008 i'd swap in another MAF and TPS to check. they don't really fail enough to warrant the expense of a new one, pick up a used on and give it a whirl. no check engine light? has it ever run right since the rebuild? is it sporadic or does it always do the same thing? Link to comment Share on other sites More sharing options...
RMVR53 Posted July 8, 2008 Author Share Posted July 8, 2008 i'd swap in another MAF and TPS to check. they don't really fail enough to warrant the expense of a new one, pick up a used on and give it a whirl. no check engine light? has it ever run right since the rebuild? is it sporadic or does it always do the same thing? yeah...if I can find one to borrow I'll swap it out. I might go chase one down in the junkyards. Does it have to come of an 87 MPFI intake? no check engine light - and it passes the forced light tests in the book. no it has not run right since the rebuild. Bill Link to comment Share on other sites More sharing options...
idosubaru Posted July 8, 2008 Share Posted July 8, 2008 important one: is it sporadic or does it always do the same thing?trying to get a feel for mechanical verses electrical. did it run right before you pulled the motor? as long as you keep the same style MAF you should be fine i think...yours is right around the cross over year so just make sure it's the flapper style (earlier) or hot wire style (later). if it's a spider manifold XT it'll be the later hot wire style. i believe that's even the same on the XT6 as well. know anyone in colorado that would lend you some sensors? i would if you were close. Link to comment Share on other sites More sharing options...
DrKrazy Posted July 8, 2008 Share Posted July 8, 2008 Tach jumping like crazy? I would assume you've checked all the connections to the coil? Hmm non-turbo MPFI, parts are hard to come by even out here. Your welcome to come dig through my spare parts stash/parts RX if you want. I got rid of most of my spider intakes and parts but I have a TON of parts for hotwire EA82T's...but not sure if the MAF is the same or not . I'm out in Golden right near 6th/I-70, PM me if your interested Edit: I remember several years ago when I put a new engine in my RX that the tach wire to the coil had actually been "disturbed" by the removal/installation process and was intermittently cutting out because that wire was grounding out several inches back from the connector. Took me awhile to figure out... disconnect the tach wire from the coil and give it run...worth the 2 mins to try. If ok trace that wire and see if it got cracked or is rubbing. Link to comment Share on other sites More sharing options...
zukiru Posted July 8, 2008 Share Posted July 8, 2008 crazy thought ... but my tach jumps... (car doesn't die but tach jumps under accel.) my problem is a rear main seal leading to a slipping clutch. the tach jump is the clutch slipping. this may not be your problem but it is mine. Link to comment Share on other sites More sharing options...
Turbone Posted July 8, 2008 Share Posted July 8, 2008 I would either suspect the coil or the disty. Usually a jumpy tach means the bushing is going bad and the disty shaft is getting sloppy. Zukiru, I dont think your tach is "jumpy". I would say it increases proportionatly when the clutch slips. Link to comment Share on other sites More sharing options...
RMVR53 Posted July 8, 2008 Author Share Posted July 8, 2008 important one:trying to get a feel for mechanical verses electrical. did it run right before you pulled the motor? as long as you keep the same style MAF you should be fine i think...yours is right around the cross over year so just make sure it's the flapper style (earlier) or hot wire style (later). if it's a spider manifold XT it'll be the later hot wire style. i believe that's even the same on the XT6 as well. know anyone in colorado that would lend you some sensors? i would if you were close. other than over heating it ran fine prior to the head swap (can't really call it a rebuild as all I did was replace the head, lap the valves and new head gaskets while I was there!) . tach wire??? what tach wire??? I have a 4 wire "harness" is the only thing coming out or going to the distributor. It is a spider manifold XT (June 87 build) oh...I forgot...new coil as well....also the power transistor Bill Link to comment Share on other sites More sharing options...
zukiru Posted July 8, 2008 Share Posted July 8, 2008 I would either suspect the coil or the disty. Usually a jumpy tach means the bushing is going bad and the disty shaft is getting sloppy. Zukiru, I dont think your tach is "jumpy". I would say it increases proportionatly when the clutch slips. still... the effect of the clutch slipping little bits at a time looked like a "jumpy" Tach.... It's also likely that my disty bushing is going out, it is 187,000 miles old.... this car has so many little quirks it loses me in the diagnostics department... at least it cranks up every day.... I think Rob is right on this .... maybe your tach issue and stalling issues aren't related? Link to comment Share on other sites More sharing options...
RMVR53 Posted July 9, 2008 Author Share Posted July 9, 2008 yeah...if I can find one to borrow I'll swap it out. I might go chase one down in the junkyards. Does it have to come of an 87 MPFI intake? no check engine light - and it passes the forced light tests in the book. no it has not run right since the rebuild. Bill got a MAF and a TPS out of an 88 XT today and put the MAF on before I ran out of daylight. same problem...actually felt like it was a little worse. I'll put on the TPS switch tomorrow. On the probability that the TPS is fine as well (sorry...being realistic - not pessimistic) any more ideas? Bill Link to comment Share on other sites More sharing options...
Turbone Posted July 9, 2008 Share Posted July 9, 2008 I would either suspect the coil or the disty. Usually a jumpy tach means the bushing is going bad and the disty shaft is getting sloppy. Have you tried changing this yet? Link to comment Share on other sites More sharing options...
RMVR53 Posted July 9, 2008 Author Share Posted July 9, 2008 Have you tried changing this yet? new coil and in the course of swapping the CAS swapped the distributor as well Bill Link to comment Share on other sites More sharing options...
McDave Posted July 9, 2008 Share Posted July 9, 2008 Since it was running fine before pulling the heads, what about ground wires? Not sure about your model but mine has a small ecu harness ground wire that attaches to the same point above the left head that the fender ground wire attaches to. Other models may have it on the intake manifold. Link to comment Share on other sites More sharing options...
RMVR53 Posted July 9, 2008 Author Share Posted July 9, 2008 Since it was running fine before pulling the heads, what about ground wires? Not sure about your model but mine has a small ecu harness ground wire that attaches to the same point above the left head that the fender ground wire attaches to. Other models may have it on the intake manifold. its on the intake on mine...and cleaned twice just for good measure! swapped the TPS this morning - still no good. Of note: since I installed the junkyard MAF I have yet to make it around the block before it starts to spit/etc. With the old MAF I could make it around the block just light on the throttle to keep it from spitting/etc. Me thinks I'm on POSSIBLY a right track here thinking its the MAF or something in that circuit? If its not the MAF, what else is there in that curcuit to check? thanks Bill Link to comment Share on other sites More sharing options...
McDave Posted July 9, 2008 Share Posted July 9, 2008 Unplug the maf and see how it runs. Link to comment Share on other sites More sharing options...
RMVR53 Posted July 12, 2008 Author Share Posted July 12, 2008 Unplug the maf and see how it runs. unplugged the MAF did the same thing once it warmed up. BUT....BUT!!! it was spittin and kickin as usual. I then stopped and unplugged the TPS switch. It ran fine...no buck/kick/miss/etc....smooth as silk. Now the odd thing is, when I swapped the MAF I also swapped the TPS so this isn't the original TPS switch. NOW what am I lookin for? Bill Link to comment Share on other sites More sharing options...
idosubaru Posted July 12, 2008 Share Posted July 12, 2008 i'd wonder if the TPS isn't bad or the wrong one. the 1987 model year, particularly with the XT, is a very strange year with significant differences based on the month of manufacturer. i have one and ran into gobs of issues like this. best solution is to verify the exact engine you need and make absolutely sure you have the right part. i ended up making a spreadsheet and documenting all the part numbers available...which were the same, which weren't, and making sure i had the right ones in my 87.5 XT Turbo engine swap. was annoying, but i think i finally figured it out. i don't think i have all that info any more though. Link to comment Share on other sites More sharing options...
RMVR53 Posted July 12, 2008 Author Share Posted July 12, 2008 i'd wonder if the TPS isn't bad or the wrong one. the 1987 model year, particularly with the XT, is a very strange year with significant differences based on the month of manufacturer. i have one and ran into gobs of issues like this. best solution is to verify the exact engine you need and make absolutely sure you have the right part. i ended up making a spreadsheet and documenting all the part numbers available...which were the same, which weren't, and making sure i had the right ones in my 87.5 XT Turbo engine swap. was annoying, but i think i finally figured it out. i don't think i have all that info any more though. As with any used part, the "new" one being bad is not out of the question. It came off an early production 88 XT so I was thinking I should be safe for a June 87 XT. While there I also pulled TPS's off an 91 Loyal/GL10 and compared it to a 88 GL and they were the same (part number/etc) to each other but were not the same as the XT. I test fitted the Loyal/GL to the XT and found while the connection is the same, the bolt up was different with the connector pointing about 30 degrees up from the XT position in the parked position. It will not bolt up to the XT in this position. I also pulled one off an 88 GL wagon turbo...similar cover but has 3 extra wires - I assume for some part of the turbo function. I have not tried it yet but assume with extra wires there is extra function but at this point I might try it. Gary/anyone know a static resistance test for a TPS switch? Bill Link to comment Share on other sites More sharing options...
McDave Posted July 12, 2008 Share Posted July 12, 2008 I would put the old tps back on the car since it ran better before you changed it. In fact I would back up and remove all the new parts that didn't help solve the problem to ensure you're not compounding the problem with crappy new/used parts. You can always put them back on later, one at a time, after you've solved the problem. Then I would get a hold of a fsm and start checking all the grounds and continuity in the wires between all the sensors (particularly the tsp) and the ecu. Check them for continuity and for shorts between themselves and to ground. With the fsm you'll have all the resistance values to check the sensors themselves too. Good luck! Link to comment Share on other sites More sharing options...
McDave Posted July 12, 2008 Share Posted July 12, 2008 One other thought. I have seen tachs themselves go bad and cause misfires, cutouts, and stalling. Disconnect the wire at the coil that feeds the tach and see how it runs. Link to comment Share on other sites More sharing options...
RMVR53 Posted July 12, 2008 Author Share Posted July 12, 2008 I would put the old tps back on the car since it ran better before you changed it. In fact I would back up and remove all the new parts that didn't help solve the problem to ensure you're not compounding the problem with crappy new/used parts. You can always put them back on later, one at a time, after you've solved the problem. Then I would get a hold of a fsm and start checking all the grounds and continuity in the wires between all the sensors (particularly the tsp) and the ecu. Check them for continuity and for shorts between themselves and to ground. With the fsm you'll have all the resistance values to check the sensors themselves too. Good luck! At this point, the TPS is the only thing not back to original...and it didn't run right with it either so its no big deal. But, I am sitting here reading the fsm MPFI diagram and I notice that the temp sensor is in the TPS circuit. So I'll swap back the original TPS, do my test drive then pull the lead off the temp sensor when it screws up and see if thats it.. Link to comment Share on other sites More sharing options...
McDave Posted July 12, 2008 Share Posted July 12, 2008 Sounds good. If you decide to check for shorts in the harness, disconnect all the sensors that are on the same circuit along with the ecu connectors. Also, in case you missed my second post here it is again... One other thought. I have seen tachs themselves go bad and cause misfires, cutouts, and stalling. Disconnect the wire at the coil that feeds the tach and see how it runs. Link to comment Share on other sites More sharing options...
RMVR53 Posted July 12, 2008 Author Share Posted July 12, 2008 At this point, the TPS is the only thing not back to original...and it didn't run right with it either so its no big deal. But, I am sitting here reading the fsm MPFI diagram and I notice that the temp sensor is in the TPS circuit. So I'll swap back the original TPS, do my test drive then pull the lead off the temp sensor when it screws up and see if thats it.. ok...never mind the street test. You can't remove the temp sensor leads with out significant moving of parts so this will be a cold/static check (after I remove 1/2 of the intake) Bill Link to comment Share on other sites More sharing options...
RMVR53 Posted July 12, 2008 Author Share Posted July 12, 2008 Sounds good. If you decide to check for shorts in the harness, disconnect all the sensors that are on the same circuit along with the ecu connectors. Also, in case you missed my second post here it is again... One other thought. I have seen tachs themselves go bad and cause misfires, cutouts, and stalling. Disconnect the wire at the coil that feeds the tach and see how it runs. thats the single black ground wire right? Link to comment Share on other sites More sharing options...
McDave Posted July 12, 2008 Share Posted July 12, 2008 thats the single black ground wire right? I don't have a wiring diagram for an XT, but it's the yellow wire on a Loyale SPFI and MPFI. Link to comment Share on other sites More sharing options...
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