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4.0 problems, BAH!

2K views 30 replies 8 participants last post by  Oldfrog 
#1 ·
Okay I've done a search but I can't find the content I'm looking for :confused:

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) :thumbsup:

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. :2thumbsup:

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? :D )

Thanks in advance, Martin.

edit: I have a 1997 ZG
 
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#2 ·
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?
 
#4 ·
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.
 
#8 ·
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.

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/f13/12-things-you-can-do-when-your-zj-stalls-1407423/?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?
 
#7 ·
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.

Second, the EML is lit.
If you mean the CEL, you can do the key trick to read codes

Third, there is a horrendous misfire:
Read the code

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/f13/12-things-you-can-do-when-your-zj-stalls-1407423/?highlight=
 
#10 ·
0 = off
1 = acc
2 = ign
3 = start

:)

I understand how to do it now though :D 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?
 
#11 ·
0 = off
1 = acc
2 = ign
3 = start

:)

I understand how to do it now though :D 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.
 
#13 ·
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.
 
#14 ·
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.
 
#16 ·
Okay, I got codes

12
25
22
27
51
55

Is there a thread which lists these codes?

I know one of them is IAC, because my dad unplugged it with the engine running. (and god knows what else, I wasn't there)

Are they stored in the order in which they were triggered?
 
#17 ·
Okay, I got codes

12
25
22
27
51
55

Is there a thread which lists these codes?

I know one of them is IAC, because my dad unplugged it with the engine running. (and god knows what else, I wasn't there)

Are they stored in the order in which they were triggered?
http://www.allpar.com/fix/80s-codes.html

If you've got a smart phone, there are also a few free apps that, well, decode the codes. I use one called OBD Error Codes that decodes both old style and obdii codes, and it's handy to have with you all the time.
 
#18 ·
Ahh good thinking! Pity, I've got the Torque app and it doesn't have the old codes :(

Okay, ignoring 12, 25, 27 (some of the injectors were unplugged) and 55.

Leaves me with code 22 and 51.

22. Coolant sensor signal out of range? Where is the coolant sensor? I find a sensor on the engine but appears to be just for the temp gage in the car?

It can't be the coolant level sensor in the reservoir, I've tested that already. it was 3.2kohm at "full" and 0 at empty.

51, O2 sensor stuck in lean position. Possible bad map sensor (that would explain the black smoke, rough idling and rich smelling exhaust fumes at hot idle?)

Is there any way I can test the map sensor, resistances etc?

Thanks for all the help so far :)
 
#19 ·
The engine temp gauge on your dash gets its info from the coolant temp sensor, because if your coolant is too hot, your engine is too hot. Though not to be confused with the ambient air temp which is just a bonus weather thing and has nothing to do with your engine, of course.
It's on the driver's side of your engine toward the back, next to your valve cover and sorta under the MAP-

http://www.olypen.com/craigh/images/tempsensor.jpg

Not sure about the map sensor though as I've never had any issues with mine, though I might remember reading that the map sensor code could have something to do with a bad or dirty IAC and possibly not the actual map, but don't quote me on that, because I could be completely wrong, lol. Just something to consider.
Anyway, it certainly won't hurt anything to clean your IAC anyway, and it's quick cheap and easy. Clean the hole it comes out of, too.

ZJ FSM
https://drive.google.com/folderview?id=0B6y1JykumBMXNWpCdk1SQTNTVFk&usp=sharing
 
#21 ·
Doing a 200 mile round trip tomorrow, unplugged the front lambda sensor, will let you know how it gets on :)

Will upload pics of my engine bay shortly, so you can see what I'm dealing with. The description and pictures shown to me do not match what I have.

That's 100% alternator in the way of No.1 spark plug and there's no air compressor :eek:
 
#26 ·
This like Where's Waldo. lol

it appears the compressor is mounted under the alternator base on the cooloant lines.

little peice of advice that may solve your problem.
get some new plug wires and route your coil wire so it does not cross the plug wires. it looks like #2 show some signs of arcing. open the hood at night and rev it up and check for blue lights.

the throttle body needs some serious cleaning.

the stud for the hot wire on the alternator looks like it's rusty

the #1 injector connector looks like it's growing something. all of the connectors need to be cleaned.

change out the idler pully or it will eat your belt

look inside the PDC for other wild life.

sorry if i sound critical, i inspect things for a living and trying to help
 
#29 ·
I'd rather someone just got to the point, I've been on many other forums and people seem so unsure when they reply or give generic googled advice. :)

I'll get right onto those things, I did suspect arcing.

Wow, I've never seen a 4.0 with the alternator on top of the A/C compressor. Is that a mod some one did, or did some ZJ's come like that?

The brake master cylinder is on the passenger side ? swapped with the coolant bottle? This is a 97 model? Not a USA model, I am assuming.
Uhh, brake MC is on your passenger side, yes. :p Not a USA model.

This is an RHD rig and it's in the UK I'm betting.
You bet right, it's a 1997 ZG :thumbsup:

UK RHD, also I think it's the ZG down under as well.

In the UK, we also have a 2.5 TD option as well - which is great for towing and having fun in the hills, as long as you watch the water temp because the gaskets are famous for failing - it was designed as a boat engine after all. :rofl:
 
#27 ·
Wow, I've never seen a 4.0 with the alternator on top of the A/C compressor. Is that a mod some one did, or did some ZJ's come like that?

The brake master cylinder is on the passenger side ? swapped with the coolant bottle? This is a 97 model? Not a USA model, I am assuming.
 
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