Need Help with my 88 307
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5.0 and 5.7 Discussion, Need Help with my 88 307 in Cadillac Engine Technical Discussion; So Ive had my car for a year now slowly fixing things up one by one. Its gotten to a ...
  1. #1
    C-Leb is offline Cadillac Owners Member
    Automobile(s): 88 Brougham
    Join Date
    Sep 2012
    Age
    28
    Posts
    28

    Need Help with my 88 307

    So Ive had my car for a year now slowly fixing things up one by one. Its gotten to a pretty good level but there is still a few small issues im having and would love to get some advice.

    Getting a bad hesitation on takeoff, worse once the car is warmed up. If I dont feather the throttle it almost wants to stall. Ive learned to live with it by feathering the throttle until it takes off and then it runs fine. Ive had the carb checked by two different old skool carb mechanics. Accelerator pump already replaced, tried isolating the diverter valve to see if that make a difference and nothing and ive already replaced the EGR valve too. I live at pretty high altitude and ive been told that the circuit from the mixture control solenoid to the knock sensor can cause problems sometimes. Im almost at the point of just going on a parts spree, O2 sensor, knock sensor, mixture control solenoid maybe some other suff...

    Tranny - Sometimes its upshifting too fast and im ending up in OD at low speeds. Higher speeds everything seems to be fine, I was going to check the adjustment on the tv cable but just for good measure Im going to do a service and change my Shift solenoid. Also since i bought it theres a 2-3 second delay anytime i put it into reverse...

    Since I first bought it the speedo has been messed up, finally i took to fixing it up last month. Changed up the ceased and rusty cable, only to find the gear was cored out. Finally after 4 weeks waiting got a new gear. Speedo still isnt working so ive dropped of the head unit to try and get rebuilt but they said these days its getting harder to find speedo head unit parts and might not be able to rebuild it. I live in Canada and was wondering if anyone knows a good place i can send it to in the states incase they cant help me.

    One other major thing ive been considering. I live close to the mountains and head out there as much as i can, the giant car with the doggy 307 works its nuts off trying to make it through the passes and with all the hills i barely ever make OD. Ive been thinking about switching to a 3.42 rear end to try and get a little more power and hopefully offset the fuel mileage by actually driving in OD more often. Also id throw in a POSI if proceeding on this en-devour.

    What do you think!!??
    Thanks
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  3. #2
    outsider is offline Cadillac Owners Connoisseur
    Automobile(s): 1987 Brougham D'Eligance, 1969 Calais Sedan, 1995 FWB
    Join Date
    Sep 2009
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    South Portland, Maine, United
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    Re: Need Help with my 88 307

    great looking car.

    1: It could be a vacuum leak or it could still be the EGR even though it's replaced. Try checking for vacuum leaks. There's a ton of hose under the hood on these 307s and one could be dry rotted and cracked on the underside so a simple visual inspection wouldn't weed it out. I've missed a cracked line on mine before and my mechanic found it after 2 hours of searching. You can also test the EGR theory by unhooking it and plugging off the lines. When I got my 87 it was actually already unhooked and plugged with a stick. when I hooked it back in I had similar problems as you're having.

  4. #3
    C-Leb is offline Cadillac Owners Member
    Automobile(s): 88 Brougham
    Join Date
    Sep 2012
    Age
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    Posts
    28

    Re: Need Help with my 88 307

    i did isolate the eger valve before replacing it and it never made a difference. I just replaced it for good measure anyways.
    Most of the vac lines have been replaced but it might not be a bad place to start, ill doo a check today

  5. #4
    sven914 is offline Cadillac Owners Connoisseur
    Join Date
    Dec 2008
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    4,164

    Re: Need Help with my 88 307

    Altitude could be playing a role in your issues. Your car's MAP sensor doubles as a Barometric pressure sensor at start-up and WOT; that's how the car's computer recalculates the altitude and fuel mixture requirements. If the Baro isn't working correctly, the computer wouldn't be able able to tell if you were driving at sea level or on top of Everest, and it would cause a lot of hesitation and low RPM issues.

    Also, you cannot diagnose a transmission until the engine is operating correctly. There should be a 2-4 second delay when shifted in to reverse, so there's no fault there. When driving on mountainous roads, you're supposed to put the transmission in manual 3rd, to prevent it from shifting to OD, so that could be why you're experiencing a lot of over shifting.

  6. #5
    C-Leb is offline Cadillac Owners Member
    Automobile(s): 88 Brougham
    Join Date
    Sep 2012
    Age
    28
    Posts
    28

    Re: Need Help with my 88 307

    Hesitation GONE!!! Map sensor, i had the best hopes for this as I live in pretty high elevation.
    Tranny fixed! My TV has a hard spot so the cable felt tight but still needed more adjustment. Good kickdowns, holds the gear properly cant wait to take it back to the mountains!

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