Sometimes when I start my jeep it will crank for a few seconds then lock up and then start and when it does this its very strange because after it starts it will have like a perfect idle that just sounds louder from the exhaust. And its solid at 900 rpm but when I try to rev it up it is slow to rev and kind of hesitant. I then shut it off and restart and its fine. Same old quiet idle. That feels bouncy but doesnt move on tach. Jeep hardly starts half the time. Is it possible for my 2.5 to temporarily sieze and then free up?
Sounds like symptoms of a head gasket to me. My 4.2 was doing something similar to that a while back and it finally got to the point the motor locked up. I pulled the plugs and spun it over and blasted coolant all over my shop wall. Don't remember which cylinder it was but R&R cyl head gasket and it fixed the problem. 2weeks later I found a 4.0 head (dammit)
You bet it would, too many people miss the obvious options to diagnose vehicle problems like a stethoscope, compression tester, vacuum gauge, and even pulling the codes where possible like post 90 wranglers!
1989 Base YJ, 4.2l, Borla exhaust, offy intake, Motorcraft 2150 carb, CRT HEI ignition, ax15, np231 JB conversions SYE, D30 ARB & Ford 8.8 ARB 4.56, 35x12.5r15 Goodyear MTR's, bds 3.5" springs, 1" body lift, and 1/2" Boom Shackles.
Build Thread: http://www.wranglerforum.com/f330/fi...ld-385106.html
Compression was actually pretty good. 135-145. I have tapping/rattling coming from the bottom when cold at idle and at about 1200rpm warm. From what ive looked into it aounds like piston slap or wrist pin noise. Oil pressure 40-60 sometimes 30 at idle when im wheelin. Besides my tapping and horrible starts the little 4 banger moves quite well around town and on the trail. I wish it was showing a code lol. I need a vacuum gauge..been lagging on it. Btw coolant is nice and green and oil looks good.
Ah I see. Guess it wouldn't hurt to make sure vacuum is in spec. I heard an exhaust leak before I removed it to do my clutch. But now its gone and sounds better. Id think an o2 would affect higher speeds and not start up. I was thinking about pulling it out of the down pipe to see if theres a difference but ive been focused on open loop. Maybe the crank sensor? Seems most likely but everything ive read on it throws me off. I did have a similar symptom yesterday, crank crank crank then it fired for a split second. I wouldn't have considered it actually being started but yeah. Do that 2 more times then by the 4th try it fired up and stayed running. But my exhaust sounded normal and it reved just fine. Seems to start differently everytime. Its very frustrating lol.
I thought about the timing chain because it used to backfire from intake on some hard starts but it hasn't done that since I fixed my iac circuit. Had code 25 and replaced the stepper motor but turned out to be a shorted wire. Iac would close off throttle bypass fully and made it so I had to hold the throttle open when starting. Can a fuel pump intermittently lose pressure? Fuel pressure test was confusing and gave me some wierd results. Trying not to confuse the hell out you guys sorry haha
While running everything is perfect. Except 2 out of 6 tests gave me a fluctuating pressure of about 30-33. Unless I revved it up or unplugged the regulator hose. Then it would steady at 39. The other tests showed 31 at idle with no needle bounce. It did this after I reinstalled the injectors. After I drove it and tested again it was back to a steady needle. Maybe the o-rings on the injectors needed some heat to seat in and become air tight who knows. But after half an hour my pressure would sometimes be 20 and then sometimes be 11. It held at 31 the longest with the fuel line pinched before the filter. One test I had it stayed at 20 for 2 hours til I reprimed for another test. Watched it climb to 44 while cranking and was hard to start still.
I only had the test kit for 48 hours. I prefer oriellys over autozone but next time ill borrow one from autozone, no time limit. That and im forgetting stuff trying to think too hard what my results were lol. Think I might try it again and make some notes/videos.