4.0 problems, BAH! - JeepForum.com

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post #1 of 31 Old 08-17-2013, 01:28 PM Thread Starter
Martin600
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1997 ZJ 
 
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4.0 problems, BAH!

Okay I've done a search but I can't find the content I'm looking for

first thing is first, the car needs the ignition to cycle a few times before a start to build up fuel pressure. weak fuel pump?

Second, the EML is lit. i'll need to get a scanner on that, my cheap ebay one can't read it any more (it used to be able to read it) but it no longer works on my 106 GTI either.

These aren't my biggest concerns though.

Third, there is a horrendous misfire: when it's COLD, and you're accelerating sometimes it hesitates and I have to put it in neutral, rev it hard a few times then it seems to be okay.

(yes the trans fluid does now at least touch the dipstick LOL and it's up to just under the max level)

When the engine is HOT, and you rev in neutral you can feel the engine running rough, you can clearly see black smoke coming from the tail pipe. When coming up to a junction, the revs dip almost down to stalling point and come back up.

I've had all 5 spark plugs out, and they are all as I'd expect them to be. No oil, not showing lean or rich condition. (I say 5 because I can't get the front one out because the alternator was making things awkward)


VIC has recently started hassling me for "coolant sensor bad" as well - I've found ways to fix that though from the forum I don't think that's related to the engine running.

Possibly unrelated, but last year the overhead showed a constant -40F for weeks on end, and now it appears to work okay.


So, any ideas? (of course you have, right? )


Thanks in advance, Martin.


edit: I have a 1997 ZG

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post #2 of 31 Old 08-17-2013, 01:38 PM
JeepNicholson
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Quote:
Originally Posted by Martin600 View Post
Okay I've done a search but I can't find the content I'm looking for

first thing is first, the car needs the ignition to cycle a few times before a start to build up fuel pressure. weak fuel pump?

Second, the EML is lit. i'll need to get a scanner on that, my cheap ebay one can't read it any more (it used to be able to read it) but it no longer works on my 106 GTI either.

These aren't my biggest concerns though.

Third, there is a horrendous misfire: when it's COLD, and you're accelerating sometimes it hesitates and I have to put it in neutral, rev it hard a few times then it seems to be okay.

(yes the trans fluid does now at least touch the dipstick LOL and it's up to just under the max level)

When the engine is HOT, and you rev in neutral you can feel the engine running rough, you can clearly see black smoke coming from the tail pipe. When coming up to a junction, the revs dip almost down to stalling point and come back up.

I've had all 5 spark plugs out, and they are all as I'd expect them to be. No oil, not showing lean or rich condition. (I say 5 because I can't get the front one out because the alternator was making things awkward)

VIC has recently started hassling me for "coolant sensor bad" as well - I've found ways to fix that though from the forum I don't think that's related to the engine running.

Possibly unrelated, but last year the overhead showed a constant -40F for weeks on end, and now it appears to work okay.

So, any ideas? (of course you have, right? )

Thanks in advance, Martin.

edit: I have a 1997 ZG
I'm no expert and I'm not gonna say this is gonna fix all your problems, but I'd start with cleaning your IAC. Rough idle, rough start, stalling can be signs of a dirty IAC. Pull it and clean it with some throttle body or carb cleaner, clean the port it goes into, too.
Also, have you actually checked the fuel pressure, or is it just acting like it isn't getting fuel?
When you turn your key to 'on' without actually starting it, you should hear your fuel pump running back toward the hatch.
And how do your battery terminals , cables, and grounds look? Nice and shiny, or dull and corroded?
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post #3 of 31 Old 08-17-2013, 01:41 PM
JasonStebbins
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1. Fuel pump or assembly.

2. Upstream oxygen sensor/TPS/Ignition coil

Poop
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post #4 of 31 Old 08-17-2013, 01:51 PM Thread Starter
Martin600
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The fuel pump does primer for 2 seconds when you put on the ignition. I don't know the pressure at the rail. What should it be? 48PSI, I found in a thread there

You can hear the pump slow down as pressure builds up, but only on the second or third cycle of the ignition. so 5-6 seconds of priming. Do these pumps have a one way valve in them?

O2 sensor was replaced a few months back

I haven't substituted the coil, but the LT resistance is what I'd expect for a working coil.

IAC has been cleaned.

I haven't checked the TPS though.

Thanks for quick replies.
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post #5 of 31 Old 08-17-2013, 01:58 PM
JeepNicholson
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Pressure should be around 49 psi

Plus or minus a few psi is acceptable

I've read things here from time to time about replacing just the pressure regulator/filter instead of the whole pump, but I can't personally vouch for it since I've never done it (if it's even your fuel pump)
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post #6 of 31 Old 08-17-2013, 03:16 PM
Rimfired
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@ op, you said you checked your plugs, how about the rotor, cap, and wires?
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post #7 of 31 Old 08-17-2013, 03:27 PM
ZeeJay1997
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Quote:
Originally Posted by Martin600 View Post
first thing is first, the car needs the ignition to cycle a few times before a start to build up fuel pressure. weak fuel pump?
Bad check valve in fuel pump regulator on top of pump.

Quote:
Originally Posted by Martin600 View Post
Second, the EML is lit.
If you mean the CEL, you can do the key trick to read codes

Quote:
Originally Posted by Martin600 View Post
Third, there is a horrendous misfire:
Read the code

Quote:
Originally Posted by Martin600 View Post
rev in neutral you can feel the engine running rough, you can clearly see black smoke coming from the tail pipe. When coming up to a junction, the revs dip almost down to stalling point and come back up.
Read the code. See this post http://www.jeepforum.com/forum/f13/1...23/?highlight=


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post #8 of 31 Old 08-17-2013, 05:17 PM Thread Starter
Martin600
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Quote:
Originally Posted by Rimfired View Post
@ op, you said you checked your plugs, how about the rotor, cap, and wires?
Haven't checked the wires, they look like they've been there a while though. maybe got a break in a few of them.

rotor and cap are spotless.

Quote:
Originally Posted by ZeeJay1997 View Post
Bad check valve in fuel pump regulator on top of pump.

If you mean the CEL, you can do the key trick to read codes

Read the code

Read the code. See this post http://www.jeepforum.com/forum/f13/1...23/?highlight=
Last time I scanned it, I got p0300 random misfire. It's more than that now but my code reader doesn't seem to be working properly.

So, the key trick. I've heard of this before.

when you say ignition on and off, does that mean between key position 0 and 2? or 1 and 2?
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post #9 of 31 Old 08-17-2013, 05:58 PM
ZeeJay1997
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Quote:
Originally Posted by Martin600 View Post
when you say ignition on and off, does that mean between key position 0 and 2? or 1 and 2?
IDK the position numbers. Stick key in hole. that is OFF. turn the top of it towards the dash until the lights come on the instrument panel. that is ON


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post #10 of 31 Old 08-17-2013, 06:26 PM Thread Starter
Martin600
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0 = off
1 = acc
2 = ign
3 = start



I understand how to do it now though I'll have a go at that tomorrow.


I see the fuel rail has a valve, like a tyre valve, presumably for fitting a pressure gauge. what is the fitting? or is there another way for me to measure fuel pressure?
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post #11 of 31 Old 08-17-2013, 07:15 PM
JeepNicholson
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Quote:
Originally Posted by Martin600 View Post
0 = off
1 = acc
2 = ign
3 = start



I understand how to do it now though I'll have a go at that tomorrow.

I see the fuel rail has a valve, like a tyre valve, presumably for fitting a pressure gauge. what is the fitting? or is there another way for me to measure fuel pressure?
You can borrow (or buy) a fuel pressure gauge at many parts stores. I believe it's a Schrader valve on the fuel rail.
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post #12 of 31 Old 08-17-2013, 08:49 PM
MaintMech
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JeepNick is correct. It is a Schrader valve and it is where you check the fuel pressure.

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post #13 of 31 Old 08-18-2013, 12:34 AM
Oldfrog
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BTW, on a 4.0, the air compressor is next to that spark plug....not the alternator. Use a wiggle joint and plug socket on a 3/8" extension to get to that plug.

I agree with Zeejay. Work through his list.
What brand of upstream 02 sensor did you install? If it wasnt NTK, replace it with an NTK.

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1997 ZJ, 4,0 select trac, Up country, track lok.
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post #14 of 31 Old 08-18-2013, 12:42 PM Thread Starter
Martin600
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I'll need to lay my hands on something that fits onto that valve. It doesn't appear to have a common pipe thread. Fuel pressure is nil after leaving the engine sitting off for 30 seconds. I can prod the valve and no fuel comes out.

Oldfrog, it's definitely an alternator and it's right in the way. I can't get the wire off! I know I could get the plug with a wobbly though I've worked in tighter bays than that. I'll get a picture so you can see. Maybe my mind is playing tricks on me.
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post #15 of 31 Old 08-18-2013, 12:50 PM
JeepNicholson
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Quote:
Originally Posted by Martin600 View Post
I'll need to lay my hands on something that fits onto that valve. It doesn't appear to have a common pipe thread. Fuel pressure is nil after leaving the engine sitting off for 30 seconds. I can prod the valve and no fuel comes out.

Oldfrog, it's definitely an alternator and it's right in the way. I can't get the wire off! I know I could get the plug with a wobbly though I've worked in tighter bays than that. I'll get a picture so you can see. Maybe my mind is playing tricks on me.
Yeah there should definitely still be around 20ish psi after the engine is shut off

Your alternator is under the air compressor, yes they look similar
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