OK obviously this is my first post. I own a 84 GMC Jimmy (35in tires, 3" body lift, around 116,000, new transmission, completely new heads) with the 6.2L. Well after finally working a good deal to get it I not have it. First off I know its sposta be loud, I have always owned Diesels(mostly Fords), but is there a quieter exhaust set up out there? Right now it is true duals out the back, with what looks like cherry bombs on there. Has anyone tried using a HMMWV intake on these engines, not the actual intake manifold the part for the air cleaner, this way it can be routed up as a snorkel. The brakes I know there are hydro, but every time I hit a puddle that is around mid tire the brake go out and the steer goes out. I know that both the system are using the PS for pressure but what would cause this to happen, got out and then take about 45sec to 1:30 to go back to normal? Last but not least who has a wiring diagram and vacuum digram for this truck? I have searched high and low but nothing seams to match up with this truck at all. The reason for the diagrams is one so I can install a radio with out blowing anything up, last owner tore the harness completely out to hack a new one in and ended up blowing out most the dash lights (which still half of them do not work even after replacing the bulbs). Then the vacuum diagram's are for the heater/AC selector and cruse control which do not work. Is there a way to test the vacuum pump?

I have found what I believe is the problem with having no vacuum to run the defroster & cruise control. So I repaired the vacuum line behind the intake & under the air cleaner, only to find another near that one, repaired that one and decided to run a test to see if i got it right, started the truck and no oil pressure. The truck runs 15W-40 Rotella T, and it was around 40 deg. outside. O ya it was a cold start also, had no been run for about 2 days. The last trip out I when mudding and was in about 2.5' of water/mud, and light snow. Also of water did splash in the engine bay, could I have killed the stock gauge or the connectors, how reliable are the guages really? Should I just get an after market and hook it up and see then? Any answers would be helpful. I'm completely new to GMC/Chevy diesels, I've always been a ford diesel guy. The second part is sense no one out there seams to have a vacuum diagram for this truck, then how many feet of 1/4" vacuum tube should I buy to replace all the under hood connections, also what other sizes and how much of it should I get? this way I do not have to take it all off and make my own diagram, I will if need be just wondering if anyone else has yet.

Thanks in advance for any help you all can offer, o ya if I posted any of this in the wrong section please tell me, I posted here cause it looks like most of out parts are specific to the diesel trucks.

Dave

Welcome to the forum! :)

Lots of stuff. Lets see. One at a time...

As far as exhaust goes the key here is the mufflers and making sure there's no leaks. I'm not sure what the brand of the mufflers I'm using is but I will have to find out as they are excellent mufflers. As with a lot of stuff you kind of get what you pay for. Cherry bombs won't do much for you (they cost what, $10 each to begin with). You need a couple of good quality mufflers that are plenty big so they don't restrict flow too much. Make sure there's no leaks at the manifolds and no holes in the pipes and it should be nice and quiet.

Don't know about the HMMWV intake but I'm sure somebody has tried it...

Don't know about the power steering. Unless the belt is getting wet and slipping somehow...

I believe I have vacuum and wiring diagrams around but I'll have to look. The wiring for the radio should be the same as a gas truck so if you look at a manual you should get some idea. On the fuse block there should be a few extra spaces mark IGN - these are switched power which can be used to run your radio. The vacuum system can be made really simple if you don't have to pass emissions (if you do let me know, I can tell you how to hook up the emissions controls - they're very simple). Ditch all the existing stuff and connect the vacuum pump directly to the one vacuum line that goes into the cab. If you have cruise and want to use it put in a T fitting and run a line to the cruise unit on the front of the engine by the injection pump (although chances are it still won't work). You can test the vacuum pump by connecting a line to it and starting the engine. Either put your finger on the end of the line and see if there is vacuum or use a gauge. To do a basic hookup I'd recommend about five feet of vacuum hose (just estimating here).

I am doubting that your truck suddenly has no oil pressure. The stock gauges are notoriously lousy and inaccurate. Still, you're better safe than sorry. I would either get a mechanical gauge (they are much more accurate and reliable) or fix the existing one.

No emissions to pass here, gotta love MI. Thanks for the tips about where to hook into the "IGN" on the fuse block to run my radio. I'm using a Chiltons manual, looking through it seams like there is a lot of difference between the gas and diesel. The book says for both diesel and gas, but tries to cover so much in so little space they leave out a ton of info I need. I'm going to get a new oil pressure gauge before I try to restart the engine, I just dont want to risk anything. I'm picking up all the parts I need Wed, so I will tell you want happens then. Any futher info untill then would be great! The diagrams would be a life saver thoe, if you can find them. Thanks for the help so far.

Dave

look at your belt for the power steering pump, see if its looks glazed. sounds like its slipping when it gets wet then catches again once its gotten rid of the water.

check the connections for the oil pressure sending unit on the motor, might have either disconnected the wires or have shorted them.

I checked the belts, sure enough glazed and one was looking kinda cracked on the inside. Well all belts have been replaced, machanical oil pressure gauge installed. I read 50psi during cold start/warm up and about 24psi during warm idle, have not driven it yet(what should it be around during operation), still got one more problem yet. Vaccum pump, how reliable are they, when I disconect the main hose it kinda makes a small squaking noise, but not sucking any air really at all (such a small amount its almost unnotisable). I know on a ford this means its dead, so I guess that same on this one to. Anything elce I should check before replacing it?

Dave

40-60psi is normal when your cruising along with the oil pressure.

the vacuum pumps on these are a much lower output than those on a ford because gm diesels dont use vacuum brakes. all its used for is some accessories such as cruise control.

Big thing with oil pressure is that it has any at all. What it actually has mainly just tells you how far along in life the engine is. What you are really looking for is not really a specific number, you want to establish a "norm".

The vacuum pumps are not very good. You can hook up a vacuum gauge and see exactly what it is doing. Doesn't actually have to do a lot so keep that in mind.