I don't understand....

[engineeradam]

I have a few questions about my 87' 6.2 diesel 1/2ton 4x4 pickup.

1. what are the two solenoids behind the air intake that have what im assuming are vacuum lines on them. they have a red and white plug on them.

2. what is the "vacuum pump's?" purpose behind the air intake? Its the thing that inserts into the block?

3.Where do the four wires off the side of my 700r4 tranny go? Because im not sure the truck is always locking up or maybe not shifting into fourth. Any checks or tests?

FYI the egr valve and the exhaust valve ie. emission control, have been removed. everything else is pretty much stock.

Thanks any guidance is appreciated. Everyone i talk to goes off of 350/gas knowledge. I need to be able to understand the the diesel fully so i can diagnose problems myself better. Thanks again.

[DmaxMaverick]

The valves at the rear of the intake are for the EGR (and possibly exhaust back-pressure valve, with some emission systems). If the EGR/emission system has been removed or modified, the valves may have no place to connect vacuum, hence their disconnect. The vacuum pump is for the EGR system and HVAC controls.

The connector at the tranny should connect to the tranny wire harness. If it's disconnected, it will not allow a TC lockup. OD with an unlocked TC doesn't "feel" like OD, with lots of TC slippage. Be very careful with this, and get it fixed ASAP. Continuing without TC lockup will overheat the tranny in a hurry. The 700R4 shift timing is internal, and not affected by external "switching" other than TV cable position (Throttle Valve, or throttle position). The open TC may make it seem like it isn't shifting correctly. Other factors may cause poor shifting, but most of the time it will be correct if it is otherwise healthy, and the TC is locking when it should. TV cable adjustment is also critical, and can cause poor shifting and tranny damage if it is not correct. If the electrical connector is disconnected, it will never lock up (no power to the internal TCC solenoid).

[engineeradam]

What is HVAC?

The wires are connected to the side of the tranny, I thought it would be the TC lockup and not overdrive but some people say the overdrive is electronic as well, is this true? or is it TV cable controlled? So where exactly do these wires on the trans go? I beleive there for brake sensor, a vacuum sensors, a 4x4 sensor and a temp sensor.

So what im wondering is where are these sensors and how do i check if there working? I want my TC lockup back. Its so nice, i thought it was OD because it just sounded like the engine use to shift into "5th" and then cruise so nicely.

[DmaxMaverick]

HVAC = Heating/Ventilation/Air Conditioning. The vent, heat and A/C controls. The 87's use vacuum to control/direct the various functions of the system. Without vacuum, the dash control will be essentially dead (A/C on-off and fan speed will work, but vent direction and heat mixing will not be controlled).

The TV cable changes the fluid pressures and shift ranges according to throttle position. If your 1-2 and 2-3 shifts seem correct, the cable is probably adjusted correctly. If it was fine before and it hasn't been messed with, it's probably OK. DO NOT try adjusting it to "improve" shift performance. It has to be adjusted correctly with a very specific process.

The OD is not electrically operated (the TCC is the only electrically controlled function). It will shift to OD when the correct conditions are in effect (wheel speed, engine RPM, throttle position). The most common cause of poor shifting (99% of the time) is a plugged fuel filter, believe it or not. If shifts are poor, delayed, or hard, replace the filter first. A plugged filter can also prevent lockup, due to greater throttle position for the given engine power output (the tranny "thinks" it's under a much higher load than actual). A bad fuel lift pump can also cause similar symptoms.

TCC lockup can be detected (or forced) via one of the ALDL (diagnostic connector under the dash) pins. I don't recall which, but can look it up. Voltage at the pin indicated a lockup command, or voltage supplied to the pin will cause a lockup condition (if ground speed and shift range is correct). Also, a bad brake switch cans prevent a lockup. If you are having issues with brake lights, the TCC may also be affected.

None of this takes into account the possibility of poor electrical connections, or chafed/broken wires. Make sure the circuits are complete, and the connectors are clean and effective.

[engineeradam]

First off thanks soo much already, im starting feel like im not going into this blind.
So ill clean electrical connections and check the fuel system first. What about this pin under the dash? A little more info on this would be much appreciated even if its just an article, id really like to learn.

Now more about this HVAC. My fan speed works, i get alright heat, but heat mixing and position setting doesn't work. How can i go about starting to diagnose/fix this problem?

[engineeradam]

oh and no AC, its a Sierra, no frills, except its a diesel.

[DmaxMaverick]

I like that: "no frills, except its a diesel". You're among friends, here.

The HVAC diagnosis..... First, verify it is vacuum controlled. Some chassis, such as Gvt. trucks, had manual (push/pull rods/cables). Check behind the control head. If it has vacuum lines to it, it's vacuum. If no vacuum lines, then you have a problem with the rods/cables. They usually wear out at bellcranks, bushings, or just rust out. If vacuum is the control, check the pump performance. The vacuum pump should pull more than 22" hg (20" is minimum spec, 22-25" is typical). If it doesn't, replacement will probably restore your vent control. You can test your vent controls by supplying vacuum to the vacuum pump outlet line from another source and try operating the controls. You should be able to hear hissing and thumping (vacuum movement and doors opening/closing). If you have vacuum and no control, lines are leaking/loose, and/or the vacuum selector valve is shot. If you hear continuous vacuum hissing w/o control movement, check for the location of the leak, and repair/replace as necessary. It's hard to say where to start on these old trucks. Time, elements, and other things can cause a long list of issues. One mouse in the works is about the worst it gets (apparently, they like the taste of vacuum lines, wires, etc.).

[engineeradam]

ok thanks a lot, ill take a look and report back. Much appreciated.

[MichDiesel6.2]

So Im looking behind the air cleaner to . Where is the air pump located ? Im fighting a shuttering and ruff Idel. My 6.2 Sierra has the 700r4 and the EGR solinoids. One is broke from its postion the bracket broke that hold the one. I1m thinking of changing the fuel filter after reading the reply here. Ill be back to let you know the out come. ( TV cable location next ).

Thanks

[engineeradam]

so mich. those solenoids just allow vacuum to pass with the throttle position sensor in the right place. so you can tear them all out with no effect. mine seized and restricted exhaust flow and alot of black smoke because the engine was suckin exhaust. most likely ruff idle is air or fuel filter. that is if it ran fine before. ie you havent played with the fuel pump. if you think its air replace the return line on top of the fuel pump with a clear line so you can see bubbles. if theres bubbles you can drill a valve stem into the gas cap making it alot easier to find leaks. cause the lines get positive pressure instead of the negative they operate at when running. as for tv cable. mine was a 50$ 20min job that was worth it. a new cable slides through the casing better then a knife in butter. my old one was hard to pull through the casing. but tv cable has nothing to do with engine just shifting