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Old 03-19-2012, 03:39 AM   #1
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lack of horsepower...

Hi guys, I'm a lifelong Jeeper with CJ's, and now I finally pulled the trigger on a YJ.

I have a '93 YJ, 2.5 no a/c. 118k miles. Bought it with the engine out(p.o. was gonna swap to a 4.0 until the ex cleaned him out).

Reinstalled the engine, which I knew had run well, here's a run down, then my question:

New dist, rotor, plugs, wires, coil, v.c.& oil pan gaskets, water pump, thermostat, radiator, fuel filter, vac lines, throttle pos sensor, idle air controller, cold air intake, electric fan and relay.

So, I get her going and she's idling hi and low alternating every few mins, but staying alive. About 350 rpm's to 1300.

I replaced the tps and iac (cleaned out the bodies too), and now she wants to die from idling too low (but still alternates to 1300 rpms every few mins)

Checked pressure on the fuel rail, 35, with fps disconnected it comes up to 45. Ign on to around 35 or so. Leak down was normal.

On the highway she accelerates sluggishly, almost like a retarded ign, but hits a sweet spot when the rpms are right. Top speed is 50-55 if the wind is right.

Compression test is unavailable for me right now but I suspect it's at least "ok"

Any ideas guys?

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Old 03-19-2012, 05:48 AM   #2
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Sounds like you need a re-gear. My 2.5L is the same way. With 33 inch tires and stock gears, it tops out about 55 and it's slow to go anywhere. As soon as I swap to 4.88 gears, should help the speed issues.

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Old 03-19-2012, 08:55 AM   #3
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If its idling back and forth it would seem there is a sensor off or not working, or a vacuum leak. I've seen the crank position sensor listed as a cause of idle problems.
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Old 03-19-2012, 10:05 AM   #4
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Check your brake booster. People always overlook it, and it can cause all kinds of issues. Then check the rest of your sensors and vacuum lines.

As for the speed, tire size can play a big part. 55mph on the speedo with 33" tires is really around 68mph on the highway.
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Old 03-19-2012, 01:06 PM   #5
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I would suspect a vacuum leak somewhere as well..
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Old 03-19-2012, 01:58 PM   #6
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I'm pretty sure the vac lines are snug, they are all new too. I'm running somewhere around 225/70/15 tires so nothing big at all.

Didn't think of the crank sensor.

What's getting me is how she'll idle around 3-400 for a few mins and hump to 1300 for a few mins. A steady vac leak should keep it steady abeit wrong.

Can the computer be getting confused by something? Maybe the distributer is off by a tooth or two? (Had the dist. off at one point.
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Old 03-19-2012, 03:08 PM   #7
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Ok figured out how to oull codes. Have a code 52 (additive adaptive memory at lean limit)

And

Code 55 (no cam sync signal at pcm open or shorted condition)

I know about the sensor on the fly wheel but wheres the cam sensor?
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Old 03-20-2012, 01:49 AM   #8
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12, 33, and 55 are normal if you don't have a/c. 55 just means its reached the end of the codes. There's a thread at JF that has all the codes:
CEL (Check Engine Light) How To. - JeepForum.com
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Old 03-20-2012, 02:17 AM   #9
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Hey thanks Pete. Have an update.

Went to visit a friend at a mech shop. He put on a timing light and found she was severely retarding. Said the pcm was getting confused because of the time. We set the dist gear ahead by a couple of teeth and the timing was perfect, with a nice advance on throttle.

Found a secondary problem too. The MAP sensor wasn't getting any vacuum. We bypassed it straight to an intake vac port and now she purrs like a kitten, steady too.

He warned me, though. Said the MAP sensor reads the vacuum from "somewhere". We would've chased it down but he had to close shop.

I did a quick follow on the vac line that runs to the MAP. All I could gather in a short time was that it seemed to come from under the jeep along the tranny.

Can anyone tell me where the MAP sensor line comes from? There was no vacuum on it, although there should have been.
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Old 03-20-2012, 02:25 AM   #10
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I've seen the crank position sensor listed as a cause of idle problems.
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Old 03-20-2012, 04:04 AM   #11
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MAP sensor should come right off the intake somewhere, probably close to the PCV source.
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Old 03-20-2012, 05:01 AM   #12
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2xs, That's what we were thinking but neither of us has had a yj or worked on that specific issue.

Just for my sanity, I'm going to replace the o2 sensor. If anything, for better mileage. At least its one less part to worry about. After that, fuel pump- UGH.......

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