QuestionQUESTION: hi tom,
i have a 1989 chevy suburban 2500 4x4 3/4 ton, 350 c.i., throttle body injection and a MSD Ignition box with variable timing. The problem started with the truck when sitting for a few weeks it wouldn't start without starting fluid. each time i was able to get it running but the problem eventually got worse. It would run but without going into a cold start. pulled the plug off the temp sensor and it came up to cold start. I changed the temp sensor. it ran for a little while then died out. next i pulled the "in" fuel line and it had plenty of fuel going in but not into the injectors so it was bypassing the TB. I put in a new fuel pressure regulator in. It ran for a week or so then started having intermittent loss of power while driving (engine pulsing). so i changed the ignition module. now it runs good but i still don't have a really good cold start unless i pull the temp sensor plug.(accelerated idle for 2/3 minutes when cold then goes to normal RPM ) I know there weren't alot of problems with the ECM/ECU's but perhaps that or PROM? What do you think?? Any Ideas on what to check next??
ANSWER: HI BOB, WELL THE FIRST THING I WOULD DO IF THIS WERE IN OUR SHOP IS RUN A DATA SCAN [PRE OBD11] OF COURSE AND SEE WHAT THE PCM IS SEEING THE COOLANT TEMP SENSOR READING AT.THIS WILL TAKE ALL OF THE GUESS WORK OUT OF IT..IT SOUNDS LIKE IT MAYBE SEEING IT AS WARMED UP MODE 195 DEGREES. BUT IF IT DOES NOT I WOULD THEN CK THE WIRING FROM THE CTS TO THE PCM SEE IF THERE ARE ANY OPENS IN THE CIRCUIT..OR JUST REMOVE THE SENSOR AND WRAP IT IN ICE AND SEE WHAT THE DATA SHOWS ON THE SCAN TOOL. THIS READING SHOULD MOVE PRETTY FAST HOT OR COLD IF THE WIRING AND PCM ARE OK...THIS DOES NOT SOUND LIKE A PROM PROBLEM TO ME. WE WANT TO SEE IF THE SENSOR IS SENDING THE READING BACK TO THE PCM.THE OTHER PROBLEM COULD BE A SLOW REACTING IAC [IDLE AIR CONTROLLER.]BUT IS SOUNDS LIKE IT MAYBE OK,BECAUSE YOU CAN FOOL IT BY REMOVING THE HARNESS TO THE CTS.. CK THIS OUT OUT AND GET BACK TO ME IF YOU CAN ON WHAT YOU FOUND....IF YOU CAN FIND A PRE OBD11 SCAN TOOL...GOOD LUCK TO YOU,,,TOM
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QUESTION: Hey Tom,
Sorry for taking so long getting back to you, Just been crazy busy. I'll do all the test's you recommend and I'll get back to you in a week or so. I'm not pressed to use the truck as I have another vehicle but I definitely need to get this problem straightened out.
Thanks,
Bob
ANSWER: OK BOB THANKS FOR LETTING ME KNOW,, AND KEEP ME UPDATED...TOM
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QUESTION: Hi Tom, Sorry I haven't gotten back to you. I've just started re-using the truck and it's running OK but there is still that underlying issue with RPM fluctuation around 1400 RPM (35 MPH). So I'm going to try to find someone to run the OBD Scan this week and I'll let you know the results. If I'm unable to find anyone with that diag tool what do you suggest I should do to address your concerns about the PCM / IAC? How will I be able to check those out? I could just replace everything but I hate just throwing money at it because you know how that works! Thanks for being patient and I'll absolutely give you the highest rating I can.
Thx,
Bob
AnswerHI BOB,BEFORE YOU GET INTO ANY THING HEAVY LIKE YOU SAID ABOVE.. TRY REMOVING THE VACUUM OR THE CONTROL TO THE EGR VALVE.WHICH EVER THIS HAS AND TRY DRIVING IT LIKE THIS SEE IF THIS STOPS SURGING...AS FAR AS CHECKING THE PCM AND IAC ALL OFF THIS CAN BEEN DONE WITH THE SCAN TOOL. THIS DOES NOT SOUND LIKE A PCM OR IAC FAULT HOWEVER..POSS TPS [THROTTLE POSITIONING SENSOR]THIS CAN ALSO BE CHECKED WITH THE SCAN TOOL....LET ME KNOW HOW THIS GOES AND GOOD LUCK TO YOU,,,TOM...
