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Thread: Wading in over my head

  1. #11
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    I checked the coolant temp sensor cold. It read 32 degrees while the overhead temp read 18. Also, the ignition advance was -21 while idling at 1500+ RPM, running the RPM up higher netted -27.

    I also looked at the calculated load, it was showing 10% at idle, but the same reading when I put the transmission in gear, brake applied. That seemed a little strange. The idle is way up there again, I'm wondering if pulling the transmission fuse and reinstalling it last night had anything to do with the sudden RPM drop and explanation for the RPM rise in gear...is there something that is triggering the IAC from the transmission that is being interpreted improperly perhaps?

  2. #12
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    Once you obtain a good manual, the interrelationship of components will be easier to track down. Regarding the ignition timing - if the distributor was installed incorrectly (out of phase) the timing will never be right.

    The park / neutral switch on the transmission (probably has 2 plugs in your application) reports gear position to the PCM & IPC. This switch also controls the backup lights, and power to the starter relay. The PCM will alter idle speed as a result of the reported gear position.

    Regarding the “load” on the engine at idle - I’m not certain if 10% with Gen I Vortecs is “normal”. With the Gen III, GM purposefully engineered in a small load at idle - to help stabilize the idle.


    Regards,
    Taz

  3. #13
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    I agree, a good manual is really needed. I just went to drive it to work and it was backfiring ( popping ) pretty badly and now it shifts out of 2nd into no gear at all, won't even drop into 4th...grrrrr! This is frustrating. Something that I did notice last night though, sitting in the driveway was that I could drop the idle down if I pushed down on the brake hard, the brake went down to the floor with some effort and the feedback was like the ABS was buzzing through the pedal. I'm wondering if I don't have a problem with the VSS, because the van has been hard to stop on the snow, the ABS seems to kick in almost immediately.

  4. #14
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    Well, to update this thread...the tranny shop I brought the truck to after I lost all gears but 2nd looked into the motor a little and believe that the 1/2 cylinders are getting raw fuel from the pressure regulator. Looking at the way the Vortec spider is laid out, I can believe that as being a possibility, and would explain partly the 12mpg I was getting, not to mention the back fires through the exhaust @ 3500rpm+...that and the arcing I noticed off at least one plug wire can't be helpful.

    They also looked into the computer and believe that it was tuned, because there are a lot of ZERO values , but also said that the cam sensor was at 9...and I saw timing at -22 at high idle, -28 @ 3500RPM.

    I'm waiting to hear back from them.

  5. #15
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    Final update to this thread, I swapped to a 411 PCM, tranny shifts fine. Still have to get the cam indexed, but the van runs nicely now. For anyone doing the 411 swap in a 98 Astro, you need to use Express van O2 sensors...trust me, this will save you a TON of headache. They ground out differently from what the 98 computer wants to see vs what the 411 wants to see. If you do the swap and you don't see the O2 sensors in a scan, then you have the wrong ones. Switching over the ends from the 4 flat to the 4 square plug our Astro's have is easy enough to do also....all you need is a paper clip. Push it into the opening under each of the pins and push. You are leveraging the tab in the pin UP and over the plastic retainer block inside the connector...then it's just a matter of matching ABCD and pushing the new pins into the old connector one at a time...takes 5 minutes.

  6. #16
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    redfury, thanks for the update.

  7. #17
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    No problem, I hate finding threads online that have no logical conclusion. Dead ended threads suck.

  8. #18
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    Well, it's time for another update to the thread now that it's been a while since I got everything sorted out. The van still runs well. I'm averaging 14.5mpg . I picked up the Torque app and a bluetooth OBD2 adapter for my smart phone. I didn't get to play with it a whole lot, but the one time I got everything to work right and had the conditions to do it, the van ( in 2wd ) did 0-60 in 7.9 sec and the quarter in 17.9 sec...think the speedo read about 90mph. This is all on a base express van tune. There is someone local that posted on CL about doing a tune for $200 for me and as soon as I can find the extra scratch, I'm going to give him a call. I'm sure with a good tune, I can get that mpg up and squeeze a little quicker times out of the van.

    I need to get the IAC out of the van and get the correct o ring on it as I had pulled it out to check it for carbon, lost the red o ring and used one that I had laying around...a little too big, and now the van doesn't like to idle at all unless you reset the IAC with the key on for 10 sec and the throttle partially depressed. I may need to replace the IAC though, with the shops scan tool, I couldn't get it to operate the IAC, or if it did, there was no change in idle speed.

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