Cranks, Wont Start - JeepForum.com
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post #1 of 17 Old 07-03-2017, 11:50 AM Thread Starter
Moses2564
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Cranks, Wont Start

Hey guys, I haven't posted here in a while, but I'm at a loss with this one.

I bought a 99 WJ with a 4.7L a few months ago for $500 with a lower end knock. Took the motor out and tore it down, and it had dropped a valve seat and destroyed the piston on the #8 cylinder. Did some light damage to the cylinder, but a dingleball hone fixed that. I honed all 8 cylinders, and threw in some new pistons, rings, rod bearings, and main bearings. Also got some remaned heads that I put on.

I've ran in to some issues though. I have no idea how long this thing sat before I got it, and it wouldn't crank when I picked it up due to someone breaking the electrical connector off of the starter when they were replacing it.

So now the issue. This thing will crank, but absolutely refuses to idle. I've got it to start, and it'll hold RPM at 2000 pretty steadily, and even freely rev up to 3000 if I blip the throttle a little. Also, it seems to be running pretty rich, some black smoke coming out of the exhaust.

Compression on all 8 cylinders is >135psi. Fuel pressure is 52 at the schrader valve on the rail. Fuel injectors read 12.5-12.75 ohms, so I know they aren't stuck open. New NGK spark plugs were installed. Coils read 2.7-3.5v with the ignition switch on. Grounds are good. New crankshaft and camshaft positioning sensors. I replaced the fuel filter / regulator with a puralator, just in case. Oil pressure reads 60 psi, which I have some zinc additives in there to break in the bearings, so that's just about right on. I've also added some fuel stabilizer, as I'm not sure the age of the fuel in the tank, and I'd prefer not to drop it.

The only code I'm throwing is a P0443 - Evap Purge Solenoid. I don't think this would cause this much of an issue though.

Does anyone have any ideas or thoughts as to what could be the problem?


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post #2 of 17 Old 07-03-2017, 02:49 PM
wadewen
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Here's the wjjeeps.com recommendation on the spark plug type. May or may not be your issue though.
Similarly, are the sensors you replaced Mopar?

If you're not sure of the age of the fuel, I'd start there...drain and replace.

Some other things that will cause your idle issue are:
Dirty or malfuntioning IAC or TB
MAP sensor
Vacuum leak
TPS
O2 sensor

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post #3 of 17 Old 07-03-2017, 03:50 PM Thread Starter
Moses2564
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Quote:
Originally Posted by wadewen View Post
Here's the wjjeeps.com recommendation on the spark plug type. May or may not be your issue though.
Similarly, are the sensors you replaced Mopar?

If you're not sure of the age of the fuel, I'd start there...drain and replace.

Some other things that will cause your idle issue are:
Dirty or malfuntioning IAC or TB
MAP sensor
Vacuum leak
TPS
O2 sensor
I'm not convinced it's the fuel. The MAP sensor is plugged in correctly, I'm going to check the voltage here after dinner. A vacuum leak is possible, but I wouldn't know from where. All of the lines to the TB are in the right place, not kinked, or cracked.

I took the IAC apart and cleaned it. It was a little gunky, but the plunger still moved freely. The O2 sensor wouldn't be an issue, as the Jeep is in open loop until it's warm, so those aren't even a factor right now.

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post #4 of 17 Old 07-03-2017, 04:28 PM Thread Starter
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Also, there seems to be exhaust coming out of the TB. And it sounds as if there's a bunch of pressure built up in the intake.

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post #5 of 17 Old 07-04-2017, 08:41 AM Thread Starter
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No ideas?

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post #6 of 17 Old 07-04-2017, 08:54 AM
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Quote:
Originally Posted by Moses2564 View Post
Also, there seems to be exhaust coming out of the TB. And it sounds as if there's a bunch of pressure built up in the intake.
That's not good. That could indicate that the cam timing is slightly off, or a valve is sticking open.
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post #7 of 17 Old 07-04-2017, 12:50 PM
wadewen
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A compression or leak-down test would be the best way to find an issue like those.

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post #8 of 17 Old 07-04-2017, 02:00 PM Thread Starter
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Originally Posted by wadewen View Post
A compression or leak-down test would be the best way to find an issue like those.
Already did a compression test. All cylinders are 135-150 psi.

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post #9 of 17 Old 07-04-2017, 07:20 PM Thread Starter
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Alright, so I'm still at a loss, here's some more things I've checked though.

Unplugged the CPS, to force the PCM in to limp mode and run a preprogrammed fuel map. Did nothing. Wouldn't start at all. Didn't throw a code.

Unplugged the CPK, because I've read if that sensor is bad unplugging it will allow the PCM to run the fuel / ignition map in limp mode again. Threw a P0320, and backfired through the intake.

Checked the primary and secondary resistance on the ignition coils. Primary was .8 ohms and secondary was ~8600 ohms. Well within specs, especially because it was 90 degrees outside.

I'm running another compression test, just to make sure. All signs are pointing towards a bad PCM, but I want to exhaust all means before I make that leap. Anybody else have any suggestions?

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post #10 of 17 Old 07-05-2017, 04:04 AM
HarryH3
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Just a WAG, but did you happen to paint the block during the rebuild? One poster recently couldn't get a fresh engine to start and discovered that one of the sensors (crank sensor?) was not getting a good ground because of the new paint he had applied. A bit of scraping to clean up around the attachment bolt and the engine fired right up.

Found it. Here's the link: http://www.jeepforum.com/forum/f310/...build-4103121/
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post #11 of 17 Old 07-05-2017, 11:59 PM
rep-tile
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Quote:
Originally Posted by Moses2564 View Post
Unplugged the CPS, to force the PCM in to limp mode and run a preprogrammed fuel map. Did nothing. Wouldn't start at all. Didn't throw a code.

Unplugged the CPK, because I've read if that sensor is bad unplugging it will allow the PCM to run the fuel / ignition map in limp mode again. Threw a P0320, and backfired through the intake.
That's a bunch of crap. The engine will not run without CPS or CPK input, period. It won't know when to fire and it won't know if you're on the compression vs exhaust stroke to actuate the fuel injectors. And since it doesn't know, it won't do either of those things.

Are you sure the CPK wasn't installed backwards? I you replaced the sensors with aftermarket sensors, you might throw them in the trash...

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post #12 of 17 Old 07-06-2017, 02:04 PM Thread Starter
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Quote:
Originally Posted by rep-tile View Post
Are you sure the CPK wasn't installed backwards? I you replaced the sensors with aftermarket sensors, you might throw them in the trash...
That is physically impossible as there is a boss on the block that prevents that exact thing. I've gone back to the original CKP and CPS, which are in fact OEM.

I am curious as to where these rumors started with the aftermarket sensors.

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post #13 of 17 Old 08-19-2017, 08:47 PM Thread Starter
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Figured out the issue. Went and did another compression test, and there was 0 compression on cylinders 2, 4 and 6. So I pulled the passenger side valve cover off, and sure enough, with the cam lobe on the closed position, those cylinders intake valves were still open, but only on one side, ie bent valve. So I pulled the passenger side head, disassembled the intake and exhaust valves on cylinders 2, 4 and 6, pulled some intake and exhaust valves from another 4.7L head I had laying around that were good, lapped and reassembled. Just set the timing, and I'm calling it a night for now. List for tomorrow:

- Valve covers
- Front timing cover
- Front drive accessories
- Intake manifold
- Throttle body
- Battery Tray
- Battery
- Put the A/C Condensor back where it goes
- Fuel Rail
- Spark Plugs

Then it should be time to fire it up.

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post #14 of 17 Old 08-20-2017, 01:00 PM
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What caused the bent valves
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post #15 of 17 Old 08-20-2017, 01:51 PM Thread Starter
Moses2564
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Quote:
Originally Posted by 86cj74.2L View Post
What caused the bent valves
The cam sprocket skipped off the dowel, so the sprocket was moving, but not the cam.

Just buttoned up all of the mechanical stuff minus the exhaust and cranked her up. Fires right up, idles perfect at 650-700, oil pressure was steady at 65psi (may seem high, but I'm running a zinc additive to break in the cams and bearings.)

Just have to reassemble the front end, exhaust, and replace some window regulators. Not bad for a $500 junkyard find.
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