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Thread: 84 Grand Marquis with engine stutter while cruising

  1. #61

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    Tps shouldn’t really be the issue as the lowest value is used as the closed throttle value for the ecu on startup. To really test it, use an analog volt meter and slowly open and close the throttle to check for voltage spikes and flat spots.


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  2. #62
    I'm an air-conditioned gypsy gadget73's Avatar
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    that should read lower than 1.4v when removed. Sounds like its bad. The ECM does self-zero but only when the TPS is within a range. I want to say its 0.8 - 1.2, but basically 1.0v +/- some amount. Pretty sure 1.38 is outside that range.

    Just to confirm you are reading from the black wire on the TPS harness to the orange one? The ground location does matter. There can be a difference between the engine block and the sensor ground. If there is, that actually might be telling us something.

    since it runs normal until warm, and for a short time after a hot restart, it has to be something with closed loop operation. I'm kind of wondering O2 sensor, or signal from the O2 sensor. I think there is an engine to ECM ground connection, and if that is bad it will skew the sensor values that the ECM sees. Not entirely sure where that lives on a CFI car, but I can go dig out my 84 wiring harness manual and look if you don't have an EVTM with the ground locations.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  3. #63

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    Hey, thanks for replying after all this time guys!

    Several online articles that I read also said the TPS self-zeros, but that it should still be within a certain range to begin with, so I ordered a new one. I did test from the orange wire to the black wire on the TPS harness. I also tested from the orange wire to the battery negative and got the exact same readings. (I think the green wire to black was a static 5.03v) I would assume that also means there's not a ground problem at least concerning that circuit? However I guess if the ECM is using a different ground then it could skew the values if that ground is bad. I don't have an EVTM so if you feel like digging out your manual to find the ground locations I'd appreciate it, unless you think that getting the same readings on the TPS from the black wire and battery negative mean that the ECM ground is ok.

    I don't have an analog volt meter, but I had someone very slowly depress the gas pedal while I watched my digital meter and I didn't see any weirdness. I will test again with the new one when it arrives. Hopefully that will be before this weekend.

    Thanks again for all the help. I feel like the car is almost there!

  4. #64

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    The green wire is 5v reference valtage so that’s good. Getting the same readings at the tps and battery means the block ground is fine so I wouldn’t look too deep into that.


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  5. #65
    I'm an air-conditioned gypsy gadget73's Avatar
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    Check from black to engine block just to confirm. It should be 0v, or very close to that. The black wire will be the ECM sensor ground. If there is some significant difference from that to the engine block, the O2 sensor will be off by that amount.

    looks like there are two ECM grounds, G105 and G108. Unfortunately this manual doesn't seem to tell me where those actually are. Assuming this is anything like the later cars, it probably connects to the rear of the intake manifold or the rear of the cylinder head. Book tells me G108 is an orange wire. Have a look around the back of the motor for a random dangling wire. The other is black/green, pretty sure thats the one up in the fender near the cruise servo.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  6. #66

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    I got the new TPS in the mail and got a break in the rain to put it on finally. It reads correctly at 0.98v KOEO closed throttle. Went ahead and put all the fiddley choke bits back together and took it for a test drive... still does it. I was so hopeful too, seeing as how the old TPS was so far out of spec. Driving it seemed to be less bad than normal. I'm not sure if that's due to the new TPS or because it was only 77 degrees when I was driving it around the neighborhood. It seems to like it better when the weather is cooler.

    I didn't get a chance to test the grounds because it started to rain on me again. However, I did test the TPS with the battery ground vs the TPS ground and there was a 0.03 or 0.04v difference between the two this time. Probably negligible?

    When I got back from test driving it I wanted to check the TPS voltage while the engine was running to see if there was any fluctuation, which there wasn't, it was at a steady 1.08v. The idle seemed a bit high and when I took the air cleaner off it went even higher because of the unplugged vacuum line, so I plugged it with a bolt and it went back down... but then after a bit it went down even more to where I feel like it should have been. I left it that way with the air cleaner off and took it for a drive, but unfortunately it's usual stutter still persisted. However, it did seem to drive a bit better that way. When I shut the engine off and started it back up again to get it to run correctly for a couple minutes it ran super fantastic. So well that I could barely feel the transmission shifts. Of course, as usual, it only lasted for two or three minutes. Incredibly frustrating.

    I'm convinced that the difference in how it runs is due to open loop mode vs closed loop mode, so it must be some sensor somewhere that's giving out bad data, or even worse, an abraded wire that's making a sensor return bad data. Is there any way to prevent the car from going into closed loop mode? I know that would hurt fuel mileage a bit, but the owner understands that it's a land yacht from decades past and she expects poor fuel mileage regardless. Also, with it in closed loop mode and stuttering, I'm sure it's getting much worse fuel mileage than open loop mode since the transmission shifts harder when it's in closed loop mode, which means I'm having to open the throttle more which pushes the TV rod more, telling the transmission to shift harder. What if I unplug the O2 sensor?

    I will check the grounding points tomorrow and I think there was something else I was supposed to check but now I can't remember. I'll have to read back through the thread.

  7. #67

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    Well holy cow, I might be on to something. I checked the grounds and they were all present, looked very good and tested within 0.02v of each other, same results checking various studs on the manifold and block and alternator body vs the battery.

    Then I was curious about the O2 sensor. I unplugged it before to see if it would make any difference, but that was when the car was acting up worse doing it's bucking and stalling related to the distributor/TFI issues. It made no difference then so I plugged it back in and left it. Today after checking the grounds I drove it around the block, more stutter as usual. I pulled into the driveway, unplugged the O2 sensor. That took maybe 10 minutes, started it back up and drove around the block some more... no stutter. I drove around the neighborhood for about 10 or 15 minutes, no stutter. Now, tonight was cooler than most nights, and last time I drove it around on a cool night it acted fine too... however, considering that it was just stuttering 10 minutes prior, I think I can assume the outside temperature isn't the cause of it not stuttering. I'm gonna test it tomorrow when it's warmer out, should be 80 or so.

    If it continues to run fine with the O2 senor unplugged, do you guys think it's because the O2 sensor is bad, or because the lack of O2 sensor data is causing the ECU to stay in open loop mode? Should I replace the O2 sensor, or just leave it unplugged? If I replace it, any recommendations for what brand to buy or not buy? Looking like Denso 234-1003 and Walker 250-21003 are options around $25.

    At this point I'd be fine with just leaving it unplugged, but it would be nice to have it fully functioning as well. I think Arquemann said he left his unplugged because it ran better that way.

  8. #68
    I'm an air-conditioned gypsy gadget73's Avatar
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    With no O2 sensor it can't run in closed loop, but bad signal from the O2 sensor will screw with how it acts in closed loop so it could be either.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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