Rough Idle

HOWDY ALL,

I am a n00b with the Mighty Max/D50 thang and as I just recently picked up a 1992 Max (AWESOME BTW) for better fuel economy. However, when I talked to the guy who I bought it from about the rough idle, he pointed out that there was a part of the vacuum system that was broken, it is a part that is bolted to the drivers side wheel well and has 3 vacuum lines going in and two elec connections. I found a guy on this site from Slidell, LA who has been overly gracious enough to help me out and sold me a couple of parts off his donor vehicle - I got the vacuum parts and stuck them on the truck (I also replaced all the vacuum lines that were connected as I figured new lines couldn't hurt), and that seemed to chill the idle out a bit, but it still is kinda rough. Can someone please help me out with the other possibilities. What other steps could I take to look into this.
TIA

welcome to the site. ive seen alot of people with rough idle problems and it seems like its something different everytime... be sure you dont have any vac. leaks anywhere n stuff like that, ive got a g52b in my truck and it had a horrible idle, advanced the timing just a bit and it cured it immediately and also picked up about 2mpgs. not saying it will help your truck but it helped mine...also on mine that will be way different then yours is i have a 32/36 weber so i dont have all those vac. lines to deal with.

OK, (pardon my greenness) but is advancing the timing as easy as moving the distributer? Just like in any of the old school vehicles? If it is in fact that easy - which direction do I turn the distributer clockwise or counter clockwise? That would be great if it is the timing.

yes it is as easy as just loosing the 12mm nut that hold the dist. in place and turning ...my advice is to turn it till you think it sound right then get a timing gun and check the marks on the crank pulley and timing belt cover..

Since you just bought the truck I'd do a compression test. Hook a vacuum guage to it as well. As far as advancing the timing goes, just advance it 'till you hear spark knock, under load, then back it off 'till the knock is gone. High test gas will let you advance a little further.

YIKES, what in the heck is a spark knock? I also have only seen a compression test done a couple of times (again, remember - I am a total noob at this stuff) when you pull a spark plug and stick that guage thing in the hole and have someone crank the engine. The truck runs like a top and the idle seems to chill out when the rpms are higher. I am going to get a timing light this evening, does anyone know where I can get a vaccum schematic/diagram for this truck? I want to check out all of the vacuum parts and make sure they are all working correctly. I am very greatful for all of the suggestions and I plan on checking out all of them too - thanks again everyone!!!

Advance your timing a bit too much and put the truck under load in a higher gear. You'll hear it. Kinda like a rattle under the hood. If you're timing is set just before spark knock you've got a maximum advance. One way we used to do it was to advance the timing 'till spark knock, w/regular gas, then fill it w/high test. Take's three or four tries sometimes. Save the money for the timing light and buy a compression tester. More info for the buck.

To do a compression test simply pull all plugs, screw the guage into each cylinder, hold the throttle open, and crank the engine 6 or 8 times. Do all 4 cylinders, record the numbers, then squirt a shot of oil into the cylinders, one at a time, and redo the test. Record the numbers. All cylinders s/b within 10% or so of each other and 140 or 150+ psi (healthy engine). The oil test will give you an aproximation of the condition of the rings, since the oil will temporarly seal the rings.

A vacuum guage will also give you a multitude of info. Usually comes w/an indicator chart. A solid 20 psi is good. If you've got a leak you'll see it on the guage. I've always got some sort of vacuum guage stuck to my dash.

Well, I bought a timing light yesterday from a guy for $10 - so that wont put me in the poor house. I will need to yank the timing cover off in order to check the timing, right? I will do the compression check to make sure things are going well too. I think I just need to spend an afternoon under the hood poking around for a bit and this advice is perfect for me. I was a mechanic in the Army - so I am familiar with things... if this was a 903 cu in Cummins engine, but it should be a lot simpler. I am relieved that there isn't a ton of plastic crap to pull off before I can even see the engine LOL!!! I am going to do what I can with everyone's advise, this site is awesome!!!

You don't need to pull anything off to set the timing. I would mark the proper setting w/some white out to make it easier to see. Don't know the proper setting for the 2.6 since I time mine by ear. It might be 5 degrees BTDC + or - 2 degrees, but I'd check that out.

if you went to autozone and buoght the haynes manual for these trucks, you will have alot of info at your finger tips. It shows all the vacuum lines going from a to b . Also it will tell you how to check timing and about everything youll need to know. Then if still confused on certain things, come and ask here.. Between both, you can fix this!