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  1. 75gmck25

    ProFlo 4 O2 Location

    Make sure the O2 bung is pointed about straight up, or not more than about 30 degrees off straight up. This should ensure moisture in the exhaust will not stay on the sensor tip as the exhaust cools.
  2. 75gmck25

    1983 AC Lines

    Are you adding A/C to a truck that had it originally? If you have the A6 already, where did you get it? The rebuilt ones don’t seem to hold up very well. You might want to also look at upgrade kits that replace the A6 with a Sanden or Seltec compressor. Lighter compressor and much small...
  3. 75gmck25

    ProFlo 4 O2 Location

    As already asked, does it use a heated sensor? Unheated sensors (usually only three wires) have to be close to the header collector so they get hot enough. Heated sensors (5 wire, etc) have a separate heating element, so they can usually be just about anywhere in the exhaust.
  4. 75gmck25

    Taillight wiring

    I am always surprised when someone does a half-assed trailer wiring mod, when you can buy a plug in connector that takes five minute (or less) to install. One example...
  5. 75gmck25

    Taillight wiring

    On a pickup there is a round wire junction/ plug up under the tailgate area, and that is where you can plug in an adapter for trailer lights. I think that is the left/right side connector for tail lights. The other key item is a fairly robust ground wire screwed to the frame, usually white color.
  6. 75gmck25

    Good sound with one pipe only

    If you watch the video posted from Enginemasters, a straight through, large case muffler (like a Magnzflow) had the best performance. I have dual 2 1/4”, H pipe and Magnaflow mufflers. It is a very moderate sound at low RPM, with some growl and rap as you run up the RPM. Never wakes up the...
  7. 75gmck25

    Ignition cylinder

    This is another source for a cylinder that seems to match your original...
  8. 75gmck25

    Well, so I bought a Toyota.

    Toyota engines have improved over the years. My current DD is a Toyota RAV4 Prime plug-in hybrid electric (PHEV). It runs 47-49 miles on a full charge, which takes about 2 1/2 hours on 240 volt, and it costs me about $2.90 for that full charge. After running out of electric I would...
  9. 75gmck25

    454 running hot

    Sending units from most parts store are incorrect for early 70’s trucks because GM no longer sells the original sensor. For my ‘75 I found the standard products TS6T has the best resistance match to the original, and also the correct nailhead connector. I also installed an aftermarket...
  10. 75gmck25

    Noob dash issues

    As already mentioned, the oil pressure gauge is mechanical, and it has a hard line running through the firewall to the engine. Sounds like someone left it disconnected. To start with electrical, first verify that there is a black ground wire running from the cluster plug over to a post on the...
  11. 75gmck25

    Crossmember?

    If the truck has the camper special or trailering special option, that may be the reason for the cut wires. My camper special wiring was cut at about that point, and it apparently used to have wires running from there up to the camper.
  12. 75gmck25

    Original or crate engine? 1976 k5 blazer Cheyenne

    You have to decide on your priorities. Matching numbers engines add significant value when you have a special high performance engine, but I doubt it is as important for our trucks. The 350 they used is a mass-produced engine with no performance features or unusual capabilities. In fact, from...
  13. 75gmck25

    Hot, hot won't start..

    Have headers may also be part of the problem, since they usually transmit more heat to the starter.
  14. 75gmck25

    Rear disc vs drum

    I have a ‘75 GMC K25 with the FF rear axle and 13” drums and they work well. Only issue I have found is that if I leave the park brake on for an extended time (days) the linings stick a little to the drum. However, it would be a PIA to do any work on them because the axle has to come out before...
  15. 75gmck25

    79 vacuum routing from canister

    One line from the canister through the firewall is a thin plastic hard line and it runs through a grommet on the firewall, across behind the dash, and connects to the HVAC controls. The other line on the canister (normal rubber vacuum line) runs over to the intake manifold and is connected to...
  16. 75gmck25

    Truck runs very very rough

    The other time I had a really rough running truck was when I was replacing a thermostat and the carburetor accidentally sucked in a piece of RTV I had scraped off the thermostat housing. I found it when someone suggested I use a mirror held at an angle to look down the carb when it was running...
  17. 75gmck25

    Truck runs very very rough

    General rough running is often due to one or more spark plugs misfiring, or there is a vacuum leak. For example, I once had a backfire pop the PCV valve up out of the grommet and the resulting vacuum leak caused a really rough idle. Look at articles on how to do a cylinder balance test by...
  18. 75gmck25

    Engine not starting

    Since it’s a hot start issue, fuel is probably the issue. However, as already suggested in previous posts, also make sure the HEI has a constant full 12 volt power feed. When you have hot start problems, try this. - get in the truck, floor the accelerator and hold it down (no pumping), then...
  19. 75gmck25

    Ignition Switch

    What is the exact problem? Doesn’t turn over the starter at all, turns over and doesn’t fire, etc. You also have an ECU, injectors, electric fuel pump, and other electronics in an ‘89, so the switch might not be the problem.
  20. 75gmck25

    AC Not Getting Cold

    Usual recommendation for R134a charge is about 75-80% of the R12 charge, so you are in the ballpark. It’s also usually recommended to use the Ford blue orifice instead of the GM white, since it usually helps cool better. Your high pressure sounds a little low for 85 degrees, but I’m not sure...
  21. 75gmck25

    Compressor not turning on.

    My refrigerant question was not planned to be complicated - the simple question is whether he know what refrigerant and oil is in his A/C. If he does not know, then troubleshooting will start with finding out what he has. Base on online info, only Washington, California and Vermont have...
  22. 75gmck25

    Compressor not turning on.

    Do you know what refrigerant you have? R134a is available from any auto parts store, but the older R12 (Freon) is much harder to find.
  23. 75gmck25

    Junction block wire started smoking when try to start?

    If you crawl under the truck and clean off the wiring terminals on the starter, one of them is the S terminal (solenoid). It may be the only one that has a single wire on the small terminal. Disconnect the wire running to the S terminal. Then if you jump/touch a short wire from the S...
  24. 75gmck25

    Junction block wire started smoking when try to start?

    Sounds like the wire running from the ignition switch to the starter solenoid. It runs over from the fuse block area to the back of the engine, and then down through a protective metal tube to the starter terminal.
  25. 75gmck25

    1986 K30 bulkhead connector wiring needs replacement.

    Don’t you have a pick and pull somewhere near you? When I lived in San Antonio there were several with old squarebody trucks and you could just pull it yourself. The bulkhead connector is in two pieces, so you can just take out the bolts that hold it together and remove it from the engine...

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