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93 Lebaron: Stalls after 40 min on track. Fine on hwy

Discussion in 'EEK! - Every Extended-K Car' started by Spank, Nov 17, 2017.

  1. Spank

    Spank New Member

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    93K mi 3.0 V6, has a later replacement auto trans.

    Car performed flawlessly for 24 straight hours at 70-80mph of steady state fwy driving. We took it on track and drove at 1/2 throttle max (in 3rd not D) with lots of accel and decel every lap, but not flooring it-- really babying it for the most part-- and it would just stall at about 40 min and die. restart would idle rough but any application of throttle would kill it. Sometimes we could get it to idle across the parking lot without dying but not always.

    If we came in and it HADN'T stalled yet, it would restart and be smooth idle, but then die pretty quickly like it suffered from heat soak during the time we performed the driver change. After about 15-25 min, it was fine again and would fire up and perform just fine for another 40ish minutes and then repeat. If it didn't stall while on track it would stall while the next driver was trying to pull out onto the track.

    While it never gave evidence of overheating (no boiling of water or blowing off of radiator cap to the overflow) the temp gauge didn't work properly (tried 2 different 1-wire senders --needle always read to the first or second line max) and the fan never turned on unless temp sender was unplugged or with our 4th wildly varying 2-wire sender) .We had 2 used 2-wire temp senders and 2 new ones. One of the new ones was about 15% different in ohms than the 2 used ones. The 4th one was wildly different spec and from Rock Auto and part # says it's for a caravan. Anyway, that 4th one would turn the fan on even if the car was only idling a short time, but when the car was cold it wouldn't idle for crap. I would plug in the old sensor even though not threaded into the block and it would idle smoothly when cold, then when the car was a little warm I could plug the new oddball sensor that WAS screwed in and it would run smoothly and the fan would also cut on. We never ran with the sender at all beyond the initial test described above because of the stumbly cold running. The problems reported were with using the 2 used senders and the 1 new sender that was 15% different.

    Another thing we found is a slight dead spot in one portion of the tps sweep at about 1/4 throttle. The car didn't really react to it, but we could find it with the multimeter.

    Things we did that we thought was fixing it but in hindsight it was just the time off track that allowed it to get fixed: cleaned the grounds under the battery and up by the alternator. Replaced the fuel pump relay (we discovered it was weak/intermittently working on the signal wire side). We replaced fuel filter, dropped the tank and inspected to see if it was gritty in there (it was clean). Checked the charcoal canister purge valve up on the passenger side-- it seemed to be fine. We suspected the ECU was getting warm (it WAS warm to the touch sometimes) so we removed driver's side headlight and put a protruding scoop for air and even put the windshield washer line into the intake so we could give it a squirt from time to time into the stock CAI to cool the ecu.

    We didn't have a fuel pressure tester, but when the car was working right we could pinch the feed line and feel the increase in pressure when blipping the throttle. But when the car was not running right, we couldn't blip the throttle because it would just cause the car to WUH -UHhh or want to die / choke out.

    Fuel tank DID get warm-- well, warmer than the chassis metal under the car.

    After the event, the car performed flawlessly driving first for 30+ min steady state on the fwy, then about 20min of stop and go, then another 20min steady state on the fwy.

    Totally flummoxed. Any ideas on what could be going on? Car is not near me currently and it's fate is unclear (currently listed for sale on CL in Houston but I may end up flying out and driving it back to SoCal). I'm just looking for a stack of possible ideas and a means to check or diagnose them for myself or to pass along to the future owner(s).

    Oh, and there was no CEL and the only time we got one or could pull codes was when we unplugged the temp sensor.
     
  2. pt006

    pt006 Active Member

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    There should not be a change in pressure in the feed line. I'm guessing the 4 cyl and 6 cyl engine fuel systems are the same. The fuel pumps put out more than enough pressure and volume for all conditions. The excess pressure and volume gets returned to the fuel tank thru the pressure regulator. This maintains a constant ~15 psi going into the throttle body.

    Low voltage or a weak ground at the fuel pump, an internal leak [hose?] inside the tank, restricted external feed line could be the cause. A fuel pressure gauge teed into the fuel feed line should help diagnose the problem.
     
    ImperialCrown likes this.
  3. ka9yhd

    ka9yhd Active Member

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    Um..... 3.0 Liter is multi point fuel injection not throttle body injection which should be about 48 psi.
     
  4. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    I don't know what all this screwing around with coolant temp sensor is supposed to accomplish. The sensor output helps vary the mixture and the ignition timing. I don't see what purpose you have in plugging it in and hanging it in free air.
    And they are negative tempco resistors, with a steep curve. I don't think you can accurately judge one against the other unless you put them in a precision oven, controlled to within 2 degrees F.
     
  5. Spank

    Spank New Member

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    I guess I should have also said I owned this car for only a couple weeks before embarking on this effort-- purchased from a 3rd party related to the elderly owner but with no history or information changing hands other than the title and what I found in the car itself.According to the smog paperwork in the car, in 2 years it had traveled less than 6k miles.Test drives of up to 1h20min in length prior to the 24hr trip provided no evidence of any significant problems (well, other than brake issues).

    My understanding of the fuel pressure is that the MAP sensor causes the regulator to switch between two different settings-- low pressure under manifold vacuum / part throttle conditions and higher pressure for low manifold vacuum /WOT conditions. Not exactly recalling if the regulator restricts the return or the feed line to increase the pressure, but that is a factory function. Blipping or revving the throttle while at idle and you can check this is working properly. Unfortunately, under the "problem" conditions, we can't blip or rev as that will choke out the motor (almost like there's a massive vacuum leak).

    Pinching closed the return line after the fuel rail SHOULD increase the fuel pressure to the injectors if the pump is working properly and a corresponding "swell" should be felt at the feed line. I can't say definitively that we could get this reaction from the car. We were a little exhausted by day 2 of this and my memory of doing this check is a little foggy

    The screwing around with the 2 different temp sensors is because 1) the temp gauge in the car wasn't or seemed to not be working and I was about to attempt to drive it 24 hours nonstop and then 14 hours on a track so knowing engine temps is kinda important 2) the fan wasn't coming on automatically and 3) the ECU is what sends the signal whether or not to turn on the cooling fan after receiving the readings from the sender. According to the Haynes/Chilton manual, the 2-wire temp sender is both for the fan and for the ecu to establish fuel mixture conditions. most modern cars have a separate thermostatic switch on the bottom of the radiator that turns on and off the fan without input fro the ecu. Chrysler chose not to do that on this car. If someone can offer what the proper OHM readings are on the temp sender when cold and when "normal operating temps" aka 200ish degrees when thermostat opens and then again when "hot" that would be a huge help in eliminating temperature sender related information impacting how the car runs.

    The purpose for having 2 different 2-wire temp senders while diagnosing--- one in the block and creating resistance based on warmth of the engine and one in free air mimicking a cold engine --- was to see if the ecu changes made to the fueling mixture based on perceived engine temp were causing the car to barely run and go into a sort of "limp mode".

    The fuel pump is certainly a prime suspect, but it is odd that only after 40min of track driving would it become a problem, and the only consistent "fix' was 15-25 min of time off the track. Full tank or 1/4 tank made no difference. Sometimes the stumbling would come and paralyze the car at 40-50mph on track and other times it would come while pulling away from a dead stop after idling for 1 minute on the way onto the track. Again, no problems on the highway either before or after the track event.

    One theory is that on the fwy it is mostly steady state throttle position whereas on the track it is constantly going from closed throttle to half throttle to closed throttle to half throttle many times every 2-1/2 miles. Could the dead spot in the tps cause the ecu to freak out and possibly get confused and overheat an internal circuit?

    I think it was temperature related but not the sole cause. The car certainly got its hottest during highway driving and coming to stops in traffic, idling in traffic at lights in Houston traffic with no fan kicking on. But I think it is an electrical circuit that is overheating rather than the engine itself. Perhaps a weak fusible link there behind the battery? Is there a known fault in a sender or sensor with these 3.0 engines I should be prepared to address?

    Thank you all for taking the time to read and offer suggestions.
     
  6. Spank

    Spank New Member

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    it acts like either the fueling is completely cut or ignition is seriously compromised. But then when it works again, it just BOOM, works again. Other theories are the coil is overheating, the ignition control circuit is overheating, or the fuel pump is overheating.
     
  7. ImperialCrown

    Level III Supporter

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    It would be nice to confirm fuel pressure when it 'leans' out.
    The fuel tank is 25 years old. The car wasn't driven much by an elderly owner and it sounds lean from your symptoms.
    Watching O2 sensor voltage when it acts up could also indicate a mixture issue.
    I would drop the tank and take a peek for water, fungus or rust debris, etc. inside. It could be ugly in there. On the track, it will be sloshing around and stirring up the crud on the bottom.
    Change the pump and sock while it is down. It may also need a tank.
     
  8. manybrews

    manybrews Active Member

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    these old K-cars and derivatives are famous for heat soak issues like this.
    however, its likely not the fuel pump. Perhaps the supply voltage to it, but you need to know for sure.
    the pump itself isnt going to be more stressed by a run around a track.. But underhood temps will spike.

    I myself have had a similar issue with one of my 3.0s, and it turned out to be the primary ignition signal. It began to operate very similar to the way you're describing on a 98 degree day with the AC on max after about 15 minutes of driving.
    No faults. Fuel pressure was clearly present (could hear the pump and smell the fuel), but it ran terribly. After cooling for 15 minutes, it fired up with no symptoms at all.

    I was able to replicate the issue and eventually found that I was sporadically loosing one of the square waves from the distributor. It ONLY happened under high heat stress.
    I just flung a new optical pickup at the distributor and the issue has been solved.

    Did you check for any faults?
     
  9. Spank

    Spank New Member

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    Firstly, I can't thank you all enough for reading and offering advice to me, a first time poster / interloper. Speaks a lot to the community you have here.

    We did drop the tank at the track. We were thinking the filter sock was clogging up. In fact, it seemed like we "fixed" the issue one time by bouncing the car up and down to rinse off the in-tank filter sock. (example of the super-awesome suspension here )

    Early on in the diagnosis the Fuel pump seemed noisier than usual-- changed fuel filter (likely the original)-- pump was quiet again. Problem persisted although we'd thought we'd fixed it. That night we dropped the tank, spotless inside, filter sock was white and clean, no replacement pumps available locally so we just buttoned it back up. Bought an external pump as a backup but didn't ever try it because the stock pump and tank looked flawless. We regret not bypassing the internal pump and trying the external inline pump, but hindsight and all...

    We did have to install a kill switch to the ignition system and main battery to pass safety regulations. We killed ignition by coming off the negative side of the coil and we put a resistor bypass that swallowed up the residual alternator charge voltage when the power was cut and the alternator was still spinning a little so we wouldn't backfeed any circuits. This bypass circuit only kicked in when the power was "killed". Since we made the initial 24hr journey prior to the killswitch installation, I suspected the wiring we did. But after the event and driving on the highway still with the killswitch installed convinced me it wasn't that wiring.

    There were no faults. Well, when we tried running with the temp sender just unplugged so the ecu would default to running the electric fan we would get the CEL for "sensor out of range" or something like that.

    We questioned the distributor pickup. When we removed the distributor cap a few hours from the end of the event, we saw it was sealed pickup area and decided not to open that can of worms. Of course, we also discovered we stripped out one distributor body hole where the cap threads down into but that didn't cause a setback but reaffirmed that it was good we didn't open up the distributor pickup area.

    I'm building a shopping list based on the recommendations here: Optical pickup for distributor. Fuel pump....
     
  10. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    we put a resistor bypass that swallowed up the residual alternator charge voltage when the power was cut and the alternator was still spinning a little so we wouldn't backfeed any circuits.
    This should be a diode, not a resistor. A resistor will allow current flow in either direction.
     
  11. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    You really need to confirm proper fuel pump pressure under all conditions. Until then, you can't rule out the fuel pump or regulator.
     
  12. Spank

    Spank New Member

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