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    Diagnosing A/C not recirculating on mac

    On mine, there is a noticeable difference in the sound of the air when on Max and the door switches from fresh air to recirculate air from inside the cabin. You can definitely hear it change from ac to max ac. If it stopped recirculating, I'd be looking at the vacuum line and the pod that...
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    Now we move into desperation territory (seeking advice)...

    There might be a sticker under the dash by the ECM that has the number in case somebody installed the wrong one? But I'd think you'd have larger drivability issues with the wrong computer. Could also be that they swapped ECM with the new body style and those got a different computer. Might have...
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    A/C only works when driving!?

    It sounds like it is likely electrical, and could be the motor or an alternator issue. But next time try to see if you can get under the hood and check the actual motor to make sure it is not doing anything vs just feeling at the vents
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    Should my TBI's fuel pressure act like this?

    right after key on, yes. it primes for 2-3 sec when key on and then the pump turns off. I don't know if it should drop to 0 during cranking, but that doesn't seem correct. have you looked in the emissions and drivability manual?
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    A/C only works when driving!?

    Air is coming from the right places on those settings
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    A/C only works when driving!?

    Are you missing the vac line that goes to the vacuum reservoir off of that T just downstream of the check valve. I dont recall my setup having a plugged T there. Or does the other line off the other T head that direction to the reservoir? Vac should be good at idle, though.....so I'd expect that...
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    A/C only works when driving!?

    not sure if the OP has specified if the blower stops or just the airflow out of the vent stops. also, try the blower on high because that bypasses the relay.
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    Should my TBI's fuel pressure act like this?

    turning the key to ON will prime the pump for a couple seconds. after the prime, the pressure will bleed off. not sure why the pressure drops to 0 for the first couple seconds of cranking. I've never done that test with mine, but intuitively it seems like the pressure should be there during...
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    Help me determine location for these wires

    1 looks like the wire to test the fuel pump with 12v that bypasses the relay. 2 I am not sure. I might run out and check my 90 burb in a bit and look around. 3 looks like the tach signal off the distributor. 4 looks like the temp sensor for the cluster. should go between plugs 1 and 3 in the...
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    ‘91 Suburban A/C Cooling Help

    I've messed with mine a bit, and i think the door is warped. So the vent settings are more like bilevel. Bilevel is like 75% floor. For AC, having a vent/floor split really is OK as it cools off high and low up front and the rear comes in high from the back. On heat, it seals up tight and only...
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    Heat/AC Blend Doors

    yes, make sure the vac lines go where they are supposed to go.
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    Started then died. Started but feather the throttle

    could be module. could be a wiring harness issue, could be stray voltage from a cracked distributor cap, could be plug wire sitting on ICM wire. but code 42 means an issue in the EST (white) wire or the bypass (tan/black) wire (open, short, seeing voltages it shouldnt) or the connector at the...
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    Heat/AC Blend Doors

    you might have the vacuum lines on the wrong ports at the hvac controls?
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    Now we move into desperation territory (seeking advice)...

    I was thinking to ONLY power cycle the fuel pump instead of cycling the key. Just trying to narrow it down. link to new ECM above. that's the same vendor I got my spare ECM from when I thought maybe my ECM was bad.
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    Now we move into desperation territory (seeking advice)...

    https://www.ebay.com/itm/224043676234?itmmeta=01J0PXNCWSQZ586H49FREZ5BXA&hash=item342a0b324a:g:4jcAAOSwSbRfd06A you will just have to swap your PROM to the new ECM.
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    Started then died. Started but feather the throttle

    Feathered the gas or gave it a lot of pedal to get it to start? Pedal down is "clear flood mode". Could be a leaking injector or something if you had the pedal down.
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    Now we move into desperation territory (seeking advice)...

    Might try not cycling the key, but instead disconnecting and reconnecting the relay for the fuel pump without touching the key. Maybe it is some fuel pump weirdness going on? That would just take the power off the fuel pump and only reset it, without resetting the ECM? I don't remember if you...
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    1990 Suburban oil pressure gauge only reads 30 PSI

    Did you pull the temp gauge and reseat it? Might just be another issue of bad contact between the gauge and the cluster housing
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    1987 Chevy v10 fires but won't stay running

    The manual says to cycle the key to on for 10sec and off for 5 sec and the start to reset the IAC. I've had better luck jumpering A and B on the ALDL and putting key to ON for 20-30 sec to let the IAC close all the way for resertinf the IAC. Pulling it out manually and then reinstalling seems to...
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    ‘91 Suburban A/C Cooling Help

    Even with the blend door all the way closed, there is still a lot of residual heat build up in the core and the hvac box. Vent setting cruising down the highway I see at least a 5 degree bump in temp from outside to vent. I've thought about installing a couple ball valves and a bypass, but was...
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    Now we move into desperation territory (seeking advice)...

    I don't know any more than what I read on their website from doing some research. But if you just want to see what the ECM sees at the sensors, how it is adjusting fuel, RPM, etc, I've been pretty darn pleased with ALDLDroid app on my phone and a Bluetooth ALDL cable from 1320 electronics.
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    Now we move into desperation territory (seeking advice)...

    You should be able to source a new ECM and swap over your PROM chip. Check Ebay. I've bought a spare for my 350TBI from there. Make sure you get the correct ECM for your year/engine. Also you could look at EBL flash II if you are looking to do more tuning and/or want a faster computer read out.
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    ‘91 Suburban A/C Cooling Help

    measure the ambient temp in front of the truck. in my limited AC experience on my burb, the engine really puts out a lot heat and the ambient temp around the engine bay might be 90-100 deg when it is 78 deg outside...
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    ‘91 Suburban A/C Cooling Help

    Biggest thing that affects ac in my burb is whether the truck has been baking in the sun for hours or parked in the shade when I get in. It takes a good long while to overcome the heat soaked metal inside the cab. That being said, I run a sanden with the rest of the stock components and a small...
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    TBI symptoms changed (new thread to reflect new problems)

    Working in that area sucks. A top creeper would be ideal. But I usually climb in and put my left foot on the passenger side frame rail and right foot back by the core support and lean in. Most of my weight is supported by the left foot. It's not comfy, but gets the job done.

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