I won't. Going to see if I can borrow a leak down tester tomorrow.

 

17 to 21 is for sea level. I live at 5500 feet and the DRB scanner reads 13.5 inches of vacuum at idle and my Jeeps haul ***.

 

Well, mine doesn't. In fact it really doesn't. It has 32s and is re geared with 4.10s, so it's going to be a little slower than stock, but 0-60 takes about 18 seconds in a vehicle that did it in about 9 stock and it won't go the speed limit on the interstate going uphill. Even with 3/4 throttle (about the limit without kicking down into 3rd) it will slow down to under 70. In this case uphill is a relative term, as it only gains 1000 feet total in 20 miles. To put this in perspective, my brother's 85 Toyota truck with a 22r and 250k easily puts my jeep to shame on the interstate, while weighing 2800 pounds and having 97 horsepower stock. Assuming my jeep to weigh about 3500 pounds, my jeep with a stock 177 hp would have 19.8 pounds per horsepower while my brother's truck all stock would have a much higher 28.8 pounds per horsepower. Something is definitely wrong with my jeep.

 

Since you have a vacuum gauge, do this test:

CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION

Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

 

2500 rpm 15 inches of vacuum, let off and it shoots to 20 and then comes back down to 13 at idle within 1 second. So, according to those results, the exhaust isn't restricting.

 

Good

 

Well, I finally have something worthy of bringing this thread back up. I finally got a compression tester, then proceeded to have to make a new end for it out of an old spark plug. Only had time to test cylinder 3, but on a warm engine it only got 70 dry and 100 with oil. It appears I was right.....

 

Check them all, with CPS unplugged and throttle floored.

 

Sorry for another long wait, with college starting and work I had forgotten about this thread. I did a compression test and got 80-85 dry and 100-105 with oil, cps disconnected and throttle floored. I also performed a leakdown test, all cylinders have serious leakage into the crankcase. In retrospect i'm not suprised the engine is worn out, as it has 206k miles and the previous owners really beat on the jeep, as within 2 years of owning it my dad had the transmission (AW4, very reliable usually) and transfer case (NP231, same) fail on him back when it had around 120k on it.

Anyway, I am picking up a rebuilt engine from a 98 ZJ that was rebuilt 30K ago on Saturday for $700 (a junkyard engine goes for 650+ around here) and doing a 99+ intake + H.O throttle body while i'm at it.

I figured out the intermittent no idle problem, the new idle air control was bad. Put the old (original as far as I know) one back in there and it now only has issues idling immediately after start. I'll get the new engine in there and if the problem persists, I'll continue working on the electrical side of things.

 

Well, to update this long dead thread.. I finally found the problem on thanksgiving.. I did swap in the new engine in 2013, just like I said I was going to. However, the idle problem remained exactly the same until the middle of September this year, when suddenly it sometimes would take 3 or 4 tries to stay running. It then went back to normal, until 2 days before thanksgiving it quit, it would die every time as soon as the ignition switch went back to the run position. After testing the ignition switch, and reading wiring diagrams, I finally found the problem.. It ended up being an intermittent fuel pump relay... which was very strange as I had moved all the relays around when it wouldn't stay running.. I cleaned the contacts and put in a spare relay (exactly the same age.. came out of a parts Jeep) and now it starts up first time, every time, into a perfect 800 RPM idle warm or cold. Very strange solution, but I thought I would update this for anyone having similar issues.

 

Could it have been cleaning the contacts was the cure?

See Tip 3.....