Sputtering/hesitation

[Musada]

I have a1990 ls 400 and the car hesitates and sputters horribly and there is some power loss. Recently my ignition coil on the driver side went out. I just gave it a tune up maybe 3 months ago, but I didn't get the fuel filter changed. Any one know what the problem could be. Money is right so I can't afford trial and error

[curiousB]

Well I would try pulling a plug wire on one bank and see if engine starts missing even more or stays the same. Reconnect it then try the same on the other side. If one side make a difference and one doesn't then dial in on the one that doesn't make a difference. Maybe its a bad coil or wiring arc'ing to chassis.

[Musada]

Well I would try pulling a plug wire on one bank and see if engine starts missing even more or stays the same. Reconnect it then try the same on the other side. If one side make a difference and one doesn't then dial in on the one that doesn't make a difference. Maybe its a bad coil or wiring arc'ing to chassis.

Whats wiring acring?

[jtbel]

If any of the spark plug wires develops a crack or break of some kind, and is touching or very close to any part of the chassis (metal), it will spark at that location. I believe I heard that you can check for arcing at night, when it is dark. I had this happen to me. One of the wires got separated from the rest and was arcing. The car had a slight miss. I don't believe the wire was cut, I just repositioned it and it stopped. Good luck.

[Bruno Molly]

THE FIX FOR ME THAT WORKED!!!!!!!

Ok... I've been chasing this problem for months.. Finally got the problem solved. NOw read carefully because these things can be like a dirt road for some people with no end.. For me, I just happen to cut down the right street before the Dead End showed up Metaphorically speaking. Ima keep it simple by listing what I did and what improvements in performance it made, the very last item I list will be the FIX to this Hesitation problem that has haunted me all this time. It may not Fix yours but it did mine. a 1993 LS400 1UZ.

PROBLEM: HESITATION ON HOT DAYS. COOL NIGHTS CAR RAN LIKE A DREAM. HOT STOP START DAYS WITH THE AC ON WERE THE WORST.

WHAT I DID:

NEW FUEL PUMP AND FILTER~ SLIGHT INCREASE IN ACCELERATION. ON COOL NIGHTS OR WHEN THE OUTSIDE TEMP WAS BELOW 90 DEGREES OR SO THE CAR WAS A ROCKET.

ON HOT DAYS....SAME PROBLEM SO NO FIX FOR POWER LOSS.....

NEW PLUGS, WIRES, DIZZY CAPS, ROTORS ~ NO FIX! SAME STUTTERING WHEN HOT.

NEW AIR FILTER~ NO FIX

MAS AIR FLOW METER ~ NO FIX

CLEANED THROTTLE POSITION SENSOR ~ NO FIX

CLEANED THROTTLE BODY ~ NO FIX

RAN 5 CANS OF SEAFOAM THROUGH FUEL SYSTEM OVER A PERIOD OF 6 MONTHS~ NO FIX

NOW FOR THE FIX....DRUM ROLL PLEASE!!!!!!

**** ENGINE COOLANT TEMPERATURE SENSOR FROM AUTOZONE...$13.99 CHANGED THE SENSOR, DROVE CAR IN 90 DEGREE HEAT, ACCELERATES LIKE A DREAM NOW! START STOP DRIVING TEST FAILED. IDLE FOR 20 MINS AND DRIVE, NAIL PEDAL, SOUNDS LIKE A STATE TROOPER CROWN VIC FROM BACK IN THE DAY WITH THE 4BB CARBS.. ABSOLUTELY NO HESITATION AT ALL. DROVE CAR 275 MILES ON A TRIP TO SEE MY SON PLAY COLLEGE FOOTBALL, ON THE HIGHWAY THE CAR FLOATED LIKE A CRUISE SHIP THE WHOLE WAY WITH THE AC ON AND NO STUTTERING.. I WOULD SAY, THIS WAS THE PROBLEM ALL ALONG, AND WAS TYPICAL FOR HOT HOT DAYS. ********

I ALSO CHANGED THE TEMPERATURE GAUGE SENDER SWITCH JUST BECAUSE I DIDN'T TRUST THE 17 YEAR OLD SENSOR IN THERE. NOT MUCH CHANGE IN NEEDLE MOVEMENT.

IT RUNS ON THE 2/5 MARK AND A SNID BIT HIGHER WHEN IDLING FOR LONG TIMES OR START ST0P DRIVING. I DID THIS FOR 2 REASONS. 1ST OF WHICH, THE TEMP GAUGE YOU ARE LOOKING AT OPERATES FROM IT'S OWN LITTLE SENSOR. THE ENGINE TEMP SENSOR SENDS IT'S INFORMATION TO THE ENGINE ECU. THAT INFORMATION YOU DONT SEE..THIS COULD BE WHAT IS BOGGING YOUR CAR DOWN.OR...LORD HELP YOU...THE ECU COULD BE FLAKY. HOT DAYS REEK HAVOC ON BAD ELECTROLYTIC CAPACITORS. 2, THE SENSORS ARE 17 YEARS OLD!!!!! THEY NEED TO BE REPLACED IMO.

MY ADVICE FOR ALL YOU GUYS OUT HERE CHASING THIS TYPICAL PROBLEM OF HESITATION AND SPUTTERING AND "DEAD PEDAL" WHEN YOU FLOOR IT ON THE HIGHWAY AND NOTHING IS THERE. BEFORE YOU GO RIPPING OUT WIRES AND PLUGS AND FUEL PUMPS START WITH THE EASY THINGS. THE ONES THAT TELL THE ECU WHAT THE ENGINE IS DOING. THINGS ATTACHED TO SENSORS..TEMPERATURE IS #1 OUTSIDE OF CPS (CAM POSITION....) AND CRANK SENSOR. IF YOUR CAR CRANKS AND RUNS WELL YOUV'E WON 1/2 THE BATTLE!!!... THE ECU TELLS YOUR ENGINE WHAT TO DO BASED ON FEEDBACK FROM THE FIELD OF SENSORS. IN MY CASE, THE SPUTTERING HAS VANISHED AND I HAVE POWER ON COMMAND NOW BY CHANGING THE ENGINE COOLANT TEMPERATURE SENSOR. I AM NOT A MECHANIC BY TRADE, BUT MY BACKGROUND IS INDUSTRIAL ELECTRONICS SO I HAVE TO HAVE A METHOD FOR TROUBLESHOOTING BECAUSE IT IS MY PROFESSION. SO MY APPROACH TO THIS WAS RATHER TYPICAL OF COMMON PROBLEMS WE ARE USE TO FAILING ON OUR AMERICAN CARS. WELL THERE'S A NEW BEAST IN TOWN CALLED PID.. (PROPORTIONAL INTEGRAL DERIVATIVE) WHICH IS A TUNING LOOP TERM FOR FEEDBACK AND CORRECTION. MY FEELING ON THIS? THE ENGINE WITH A FAULTY SENSOR, THE ENGINE EITHER THINKS THE ENGINE IS TOO HOT AND CUTS CERTAIN BANKS OF FUEL OUT. CORRECT ME IF I'M WRONG, BUT IF THE ECU FELT THE ENGINE WERE TOO COLD WOULDN'T IT JUST DUMP FUEL VIA COLD START INJECTOR THUS LOADING UP THE ENGINE WITH TOO MUCH FUEL? I DON'T KNOW..ALL i KNOW IS ALL THE TIME I SPENT CHANGING FUEL PUMPS, IGNITION WIRES, ALL THAT WAS NEEDED ANYWAY....BUT THE 1000 DOLLA WINNER IS THE ENGINE TEMP SENSOR LOCATED BEHIND THE IGN COIL DOWN ON THE INTAKE COOLANT PASSAGE. IT TAKES A 3/4" SOCKET i THINK...THE CONNECTOR OF THE SENSOR IS GREEN. THE GAGE SENDER SWITCH IS A TINY SINGLE TERMINAL SWITCH THAT TAKES A 12MM DEEP WELL TO GET OUT..ALSO LOCATED RIGHT BEHIND THE CENTER IGNITION COIL ON THE COOLANT PASSAGE. I HAVE A 93 LS400. IF YOU JUST BOUGHT YOUR CAR, IT IS NEW TO YOU..BUT SENSORS UNDER THE HOOD THAT TELL THE ENGINE ECU THE VITALS ARE PROBABLY AS OLD AS THE CAR. START THERE 1ST!!!!!! IT MIGHT SAVE YOU TIME AND MONEY $ $ $ $ $ . JUST MY 2 CENTS AND FINALLY..SOME CLOSURE. HOPE THIS HELPS YALL. IT MAY NOT..BUT IT GIVE IT A TRY.

IF THIS HELPED YOU, AND YOU ARE IN A POSITION THAT YOU CAN, PLEASE DONATE TO MY PAYPAL $1 (ZULE8313@AOL.COM) OR WHAT EVER YOU FEEL THIS INFORMATION IS WORTH SINCE I AM BETWEEN JOBS RIGHT NOW AND HAVE 2 KIDS IN COLLEGE. I NEEDED THIS TRIP! MY SON RECOVERED A FUMBLE EVEN THOUGH THEY LOST, BUT I AM SO ECSTATIC THAT MY CAR IS FIXED FROM A $13 SENSOR AFTER I HAVE SPENT OVER $500 IN FUEL DELIVERY AND IGNITION COMPONENTS...

THANKS TO COMFORT INN FOR LETTING ME USE THEIR INTERNET BEFORE MY 4 HR DRIVE HOME. GOOD LUCK LEXIES!!

BRUNO MOLLY

[curiousB]

Congrats, nice outcome and good writeup. Hopefully will save some others for a few dead ends.

These cars are complicated closed loop control systems. So a failed input sensor can create strange effects. It seems the ECU isn't too smart about determining out of range input on the temp sensor (or at least unlikely range). It would seems a couple more lines of software code would be all that is required. IE why was the average resistance x ohms for a warm engine for 8+ years and then suddenly its y ohms which is >50% different?? Also if engine has been running for >20 minutes and temp sensor says cold then ignore temp sensor log a CEL error for bad coolant sensor and trim engine fuel/air for a normal temperature, that would be better than taking an obviously wrong input and driving fuel/air completely off the mark.

Can you measure the old sensor with a DVM? I'd be interesting if the sensor failed to:

1) An open circuit (resistance -> infinity)

2) A short circuit (resistance close to zero ohms)

3) Some other value and temperature varying but not on the resistance/temp curve the ECU expects?

I suspect it is #1 and that might lend itself to a simple check with a DVM of pulling the connector wiring and probing the sensor.

Was your gas mileage poor these past few months? Was the car running too rich?