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I just did a enginge swap in a auto 4x4 84gmc 2500 6.2 diesel. the diesel I put in was out of a auto 2wheel 82 c20. I can't figure out the vacuum lines and there is no sticker. I can only find one source of vacuum and that is off the vaccuum pump. see 3 vacuum nipples on the engine that need filled. 2 on the vacuum reg and one on the throttle position sensor (I think that is what they are) and then there is a 4th on a diaphram on the tranny. I currently have a single hose going off the v.pump to the tranny cause it is the only way I could get it to shift at a decent rpm. other routing I tried left the tranny shifting @ high rpm.
thanks
Evan
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get emmissions t's and it sounds like some solenoids are missing
 

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Here's a shot from my "84 GMC w/6.2 front decal.
Hopefully it'll come through.

Tom
 

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Here's a shot from my "84 GMC w/6.2 front decal.
Hopefully it'll come through.

Tom
Being its out of a 2500, wouldn't it be a j engine with no emissions needs? Aside for the transmission, vacuum is for cruise and ac/heater controls only? At least, that's all mine is used for.

Peyton
 

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Do not opperate the truck with the vacuum line directly to the trans! (Since it has a vacuum diaphram, I assume it's a TH400). TH400s use the engine vacuum on gas engines to determine load. ie: full vacuum means carburator is closed (idle), no (very little) vacuum means carb is open (full load). So if you are driving around like this, the trans is going to shift like it thinks the engine is just puttering around in a parking lot. You're going to get a lot of slippage that will damage the transmission eventually.

You need to buy some "emissions tees" and split off from the vacuum pump. One hose should run to the firewall (for the heater controls), one should run to the cruise control module, and one should run to the throttle position sensor on the IP then to the transmission.

One more thing, you need to be sure your throttle position sensor is from an engine equipped with the same type transmission! They apply power to the trans at opposite ends of pedal travel. I murdered my 700R4 in a matter of months because I had a TH400 TPS on my IP and didn't know it.
 

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A 2500 may or may not have emissions controls depending on GVWR. Over 8500 lbs and all military vehicles regardless of GVWR had a J-code, non-emissions engine. All civilian vehicles under 8500 lbs. GVWR had a C-code, EGR/EPR-equipped emissions compliant engine. In general, vehicles with C-code engines usually had 700R4 four speed automatics which did not utilize vacuum but instead were equipped with a cable from the throttle shaft to operate the throttle valve in the transmission. Vehicles with J-code engines usually had TH400 three speed automatics which used a vacuum signal which came from a vacuum regulator valve on the throttle shaft of the injection pump.

The vacuum system on one of these trucks is, in reality, quite simple. There are very few things that operate off of vacuum. Light duty trucks with 700R4s and C-code emissions are the most complex (made more complex if you have cruise). Basically, right above the vacuum pump there would be a T fitting. One line off of the T would go to the driver's side of the engine, where there are EGR and EPR control solenoids (controlled by means of the TPS - Throttle Position Switch - on the passenger side of the injection pump). There would be two lines from there, one from each solenoid. One line would go through the air cleaner to the EGR valve and the other would go to the EPR valves on the exhaust manifold. The other side of the T would go into the cab to run the heater and A/C. There are also some lines for the cruise control, one of which runs along the passenger side of the engine and then across the front to the cruise actuator, another of which winds up at a vacuum switch on the brake pedal. I'm guessing that those haven't been disturbed, though, and chances are you don't care about the cruise anyway. Mostly it is the emissions/heater controls that get messed with.

J-code engines are even simpler. They basically just have a line that runs the heater and A/C and the cruise if the truck is so equipped. They do have a vacuum line that runs to the VRV on the passenger side of the injection pump and then another line from there to the transmission, but otherwise they are very simple. Many people set up their C-code engines the same way, ignoring the emissions controls.
 
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