4.0L Multiple Cylinder misfire

[JPNinPA]

"Autolite 985", not sure, can't recall if they're APP or AP. They don't read "Platinum", is that what the second "P" is for?

985 copper
AP985 single platinum
APP985 double platinum
Being a97 tj you only need single platinum. Double won't hurt unless your coil energy is low.

Backing up a bit. What have you checked, found and changed?
When does it backfire? Do you notice anything?

 

[Ynot]

Backing up a bit. What have you checked, found and changed?
When does it backfire? Do you notice anything?

It doesn't backfire at all, runs very smooth. If the check engine light were never on you'd never know there was a problem.

Instead of posting everything that I've done please see this post. I'm "T's '97TJ". It'll probably help out more than me bumbling things up by reposting.

 

[JPNinPA]

It doesn't backfire at all, runs very smooth. If the check engine light were never on you'd never know there was a problem. Instead of posting everything that I've done please see this post. I'm "T's '97TJ". It'll probably help out more than me bumbling things up by reposting.

Ok I needed to re read it all.. Then codes show up after you reach 65 mph and not before. Even then it feels smooth but the CEL comes on.

Have you checked your fuel pressure at idle and up to WOT?
Also what rpm do you idle at? Do this after resetting the codes and clearing the PCM memory by disconnecting the battery and turning the key to on. Then depress the trip odometer after reconnecting the battery.

 

[Ynot]

Then codes show up after you reach 65 mph and not before. Even then it feels smooth but the CEL comes on.

Yes

Have you checked your fuel pressure at idle and up to WOT?

Yes, see previous included link. What is "up to WOT?"?

Also what rpm do you idle at?

Just under 1k

 

[JPNinPA]

I read the other thread. Those are knowledgable guys helping you there.


The only thing I could tell you besides what they covered is possible intake leak or intake to exhaust. This why I asked about idle rpm after resetting the PCM. If it were 1k or higher it would be a leak. Besides this measure the voltage at the fuel pump when the key is turned on. It should be close to 12 v. Lower voltage could cause intermittent issues while driving wile depressing the gas pedal more. You have a check valve issue and the 47 psi is at the 49 +/-2 psi spec.


Btw what rpm are you at when going 65 mph? We often don't consider everyone has different tire size and gearing... Low gearing and higher rpm you are likely consuming more fuel per min than taller gears at lower rpm. This will be more sensitive to lean conditions.

 

[Ynot]

Btw what rpm are you at when going 65 mph? We often don't consider everyone has different tire size and gearing... Low gearing and higher rpm you are likely consuming more fuel per min than taller gears at lower rpm. This will be more sensitive to lean conditions.

First, thanks for reading that thread and putting in the time, I do appreciate it.

I drove on the fwy to pick my kid up at school today. At 65mph it was just over 2500rpm, at 75mph it was just over 3000. The interesting thing was by those speeds the "Check Engine" light would have come on. I'm wondering if resetting this time really took or if this is just a fluke and it'll hit in a few days more driving. Since the last time I reset it I believe I did the plugs, oil and oil filter. I'm crossing my fingers and toes as I'm about to sell this and don't want to go the extent of a head rebuild if I can help it.

 

[JPNinPA]

Those RPMs are low. If over 3200 at 65 may have been an issue.

 

[Ynot]

measure the voltage at the fuel pump when the key is turned on. It should be close to 12 v. Lower voltage could cause intermittent issues while driving wile depressing the gas pedal more.

I just finished a valve job. Pulled the head and took it to a shop. They also put in all new springs and replaced valves where they were worn. I buttoned it all up the other day cleared the old codes and 47 miles later they came back.

Today I'll be running a new compression test.

How do I check the fuel pump voltage?

You have a check valve issue and the 47 psi is at the 49 +/-2 psi spec.

What does this mean? How do I fix it?

Thx

 

[JPNinPA]

The answer to the 47 vs 49. +/-2 is to replace the pump and fuel filter.
What it means is at WOT not enough gas is delivered and atomized. Your running lean. Did you find burnt valves?

The correct way to test the voltage at the pump is dropping the tank. Other than that is splicing in near the tank but that doesn't include the last 3 ft plus connections.

Being you took the head off ... Be sure the misfires are not from a leak around the head, intake, plugs, injectors... Bad plug. They are easy and cheaper than dropping the tank.

 

[Ynot]

The answer to the 47 vs 49. +/-2 is to replace the pump and fuel filter.
Did you find burnt valves?

No. 2 were worn and 1 was close to worn so he changed all 3. The rest were fine. None burnt. Any other signs of running lean?

Being you took the head off ... Be sure the misfires are not from a leak around the head, intake, plugs, injectors... Bad plug. They are easy and cheaper than dropping the tank.

As far as the misfire codes, they're all the same as before, with the exception of 1 less (PO302 Cylinder 2 Misfire Detected):

PO300 Random/Multiple Cylinder Misfire Detected
PO304 Cylinder 4 Misfire Detected
PO305 Cylinder 5 Misfire Detected
PO306 Cylinder 6 Misfire Detected

Honestly, I'd have to rule out an intake gasket leak and plugs. If you mean the intake gasket, it was torqued to spec and to get the exact same errors in the same cylinders would be a heck of a coincidence. If you mean hoses and connections to the intake I'll double check them. Same goes with the plugs, unless it was just one. When I reinstalled them they were not in the same same order, yet again I have the same 3 remaining errors in the same cylinders. If they were the wrong plugs altogether I'd replace them all. They looked great when I re-gapped and reinstalled btw. Nice and clean.

Along with a compression test today, I also plan to swap 2 injectors tomorrow to see if one of the errors follows the injector to a new spot. While I'm at it I'll install new O-rings.

Any chance it could be the coil or distributor? If so, can these be tested?

EDIT:

Latest compression results:


Cyl#
1 ------160psi
2 ------160
3 ------165
4 ------165
5 ------163
6 ------160


Overall the compression has improved since the original test. Cyl.#3 was the only one that decreased from 175 to 165.


Again the engine was warm and all the plugs were pulled. The coil was disconnected as well as the FP fuse. I let it crank about 5 times.


For the heck of it I swapped plug wires 3 and 4 to see if the problem follows.


Today, when I hit about 52 miles, since the last code reset, the CEL came on. I was go down a slight incline at the time on the freeway, 3000rpm @75mph. I also happened to be recording it at the time. See 00:39. www.youtube.com/watch?v=nXL0MvfUIS8


When I got home I read the codes. All the same plus a bonus PO 441 code = EVAP... Purge Flow Fault. I checked my gas cap and hoses at the purge solinoid and they seem fine. I'll let this one ride for a while and recheck the codes after the next reset.


The only things I've done different since the last reset is clean up some grounding straps and ran the above compression test, during which I smelt gas which may have to do with the 441 code.

 

[Ynot]

Misfires FIXED - Crankshaft Position Sensor!

Had the 441 code still this morning. Ended up emptying out charcoal from the upper hose on the purge solenoid. During my head rebuild I accidentally flipped the canister over, so wonder if this had something to do with it. If there's still a problem it should pop up again with 100 miles.

 

[JPNinPA]

Glad to hear you got it fixed ... So valves and crank sensor on the bell housing.

Most of the time the CKP just quits and engine shuts down.

Good job! Sticking with it.

 

[Fl0pp]

I have a 2000 2.5L jeep wrangler, well my son does and hewas stranded over 300 miles away and I had to tow him back because I could notfix a similar problem, multiple misfires and valve 2 misfire.
Replaced wires, (he broke one checking)... He was moving home and had theTrans rebuilt. Drove over 500 miles then I get a call. It just diedand wont start, when he was checking he broke a wire, I came with wires and wegot it to an Auto Zone. It was burning rich, I could smell itfollowing. It would not stay running well and it got up to 60 mph, but hadno power at all, when I sprayed ether in the throttle body and it would die.got the code of multiple misfires, replaced cap and rotor. same code replacedthe plugs, #2 was a little dirty, but looked good. but I had gotten the same, Iwill have to post what plugs they are. ( the $3 ea ones with the needlelike cathode). Then I got a misfire on 2, I replaced the Crank sensor, checkedthe fuel pressure, Cleaned as best I could the Idle air sensor (It was alldirty and I got it shiny). So Being that I was not going to spend a day andmore money, I towed it home til a cop pulled me over cause the batterydied for its flashers, but the Battery is amazing, terminals clean, and I haveordered a throttle position sensor. any advice would be cool.

 

[Ynot]

1st, sorry to hear about the misfire issue, I know how incredibly frustrating it can be. To tell you the truth I sold my TJ just after all the repairs, so bare with me.

One sensor that I was considering changing was the Cam Position Sensor located in my distributor. You may want to check that out. At one point I believe I did remove it and clean it up.

Make sure you're running the correct plugs for your motor. Search the forum for your 2.5 as I had a 4.0, so not sure.

Check your coil. As I recall Auto Zone did this while they were checking out my alternator.

Check your grounds. There was one from the back of the motor to my firewall, but again mine was a 4L. For me there was also one down near the distributor, but my memory is crap, so I can't remember for sure, sorry. Don't just look at them, take them off sand them clean and reconnect them.

The only other advice I can give and it's a real PITA, is check every wired connection in your engine compartment especially the ones that have to do with your injectors and any sensors. Get some electrical connector cleaner, open them up, hit them wipe them clean and dry and connect them again. Just be easy pulling them apart as the plastic may be brittle. If any wires have any splits fix them right, replace them, tape them up, solder them, whatever it takes for good consistent power.

If this doesn't help keep searching any Wrangler forum, Youtube and Google. Also keep in mind that this engine was used in multiple vehicles, so don't feel that only TJ owners may have this or any problem you come across. I got a most of the help with my head replacement from a Cherokee forum.

Good-luck

 

[JPNinPA]

2X on cleaning the grounds where they contact the body and engine.
Poor battery or connections will reek havoc on the engine operation. If you take an ohm meter between the battery negative terminal and somewhere on the body (I use the door catch on the body) the resistance should be less than 5 ohms.
Running rich and spray ether causing it to shutter sounds more like a injector issue. You could have a stuck injector flooding the cylinder. If you can't start try holding the pedal to the floor. This shuts off the fuel pump allowing any fuel in the cylinder to be pushed out. This only confirms an issue do not run like this.

 

[JLev912]

Hey y'all, been searching all the forums and all the threads trying to fix this same posted issue, but here's the background:
2000 TJ 4.0 brought it down to VA where myself and some good friends swapped out the front D30 with a HP D30, swapped out the stock rear D35 and put in a D44. Did a tummy tuck while we were down there, and changed out some worn suspension parts. The only electrical work done was installing the locker switch, oh yeah forgot to mention I had an eaton e-locker installed in the front before we mounted it =0)
Also worth noting I strayed from stook gearing and had front and back geared 4:88.
Now, after all the work was done I tested it out and all was well and started my journey driving it back to NJ. 10 miles down the road the CEL was FLASHING so stopped at Auto zone and had them read the codes which were multiple cylinder misfire and a bunch of cylinder misfire codes. So I bought new plugs, drive back to my buddies, and did a quick spark plug swap. Cleared the code, got back on the road and the same thing happened. The jeep felt like it was driving fine other than the speedometer being WAY off, and the RPMS running higher than normal, but I expected it due to the gear changes.
Anyway, the problem is still there.. I reset the code and jeep runs great. The CEL comes back on and only then does the jeep feel like it's sputtering when I idle or put her in reverse. If I clear the code it goes away until it is triggered again. I don't get it... but it seems way too much a coincidence that the problem started once I swapped out the rears. Could it be the altered speedo or tach readings not fairing well with the ECM? Everyone on the thread is talking about valves and cylinders, but it seems unlikely that the valve springs would go bad as soon as I put the new axles in. Anyway, just throwing it all out there, hopefully something clicks with someone. Thanks in advance!

 

[Brian Koerner]

I have a 2001 wj 4.0 4x4 auto has 254k i have done as followed put a clutch fan in replaced thermostat put new champion plugs gapped to .35 replaced coil pack replaced fuel pump replaced injectors now the issues that I've been fighting to no avail is p0300 p0305 p0304 upon visual inspection I have no crack in head an there is no milky substance in oil need help inspection expired two days ago

 

[cpicelle]

Out of nowhere, my 2003 TJ has just started displaying all of these symptoms. Seems that nobody has finalized the true fix? I will not be doing the mechanical work, but would like to give my mechanic an exact path to follow with the least wasted money on replacing parts that really don't need replaced. Any new news here?

 

[Ynot]

Mine ended up being the Crankshaft Position Sensor. $35 and took about 15 minutes. This after lots of work shown earlier in this thread. So, can't hurt to start there.

 

[cpicelle]

Fingers crossed, just received a phone call, seems my plugs were complete junk, burnt out to as much as .85 gap. New plugs, and it is related that it is firing perfectly. We'll see...