4.0 issues

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Shagoneer
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Re: 4.0 issues

Post by Shagoneer »

Alright, I know my local yard doesn't have any wranglers of any generation, but they have a TON of XJs
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tedlovesjeeps71
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Re: 4.0 issues

Post by tedlovesjeeps71 »

Shagoneer wrote:Alright, I know my local yard doesn't have any wranglers of any generation, but they have a TON of XJs
I've been pondering how to verify if it'll work or not. I can't think of any reason a computer for a 4.0 from any similar Jeep wouldn't work in a CJ. Unless there was something special in the computer that recognizes a TJ (programming based on vin? You said the motor is from a 96?98 TJ?? Maybe find the same year Xj and give it a try.


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Re: 4.0 issues

Post by Shagoneer »

I'll give a Cherokee ecm a try, I just wasn't sure if it would work since the cherokees have all the anti theft sensors if it would freak out in something else.
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tedlovesjeeps71
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Re: 4.0 issues

Post by tedlovesjeeps71 »

Shagoneer wrote:I'll give a Cherokee ecm a try, I just wasn't sure if it would work since the cherokees have all the anti theft sensors if it would freak out in something else.
It's an interesting question to say the least. If it were trying to take an ECM from say an 01XJ and put it in a 91 YJ, there may be an issue. Maybe not? Since it's going in an older CJ, there's no telling what was used and what wasn't. If you had access to shopkey or all data maybe you could pour over the schematics and compare them. An easier approach may be contact someone that sells the ECM and see if there are years that share the same part number? If a 98 TJ and a 98 XJ have the same number, it's a win?
Out of curiosity, have you hooked a scan tool up to it to see if it has any issues? It could have a problem that doesn't cause a CEL but does make for a no-start.
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Re: 4.0 issues

Post by Stuka »

tedlovesjeeps71 wrote:
Shagoneer wrote:I'll give a Cherokee ecm a try, I just wasn't sure if it would work since the cherokees have all the anti theft sensors if it would freak out in something else.
It's an interesting question to say the least. If it were trying to take an ECM from say an 01XJ and put it in a 91 YJ, there may be an issue. Maybe not? Since it's going in an older CJ, there's no telling what was used and what wasn't. If you had access to shopkey or all data maybe you could pour over the schematics and compare them. An easier approach may be contact someone that sells the ECM and see if there are years that share the same part number? If a 98 TJ and a 98 XJ have the same number, it's a win?
Out of curiosity, have you hooked a scan tool up to it to see if it has any issues? It could have a problem that doesn't cause a CEL but does make for a no-start.
The engine was swapped into the CJ. CJ's never came with 4.0's.

Shagoneer: Not all XJ's have anti-theft. Actually, most do not. That was more of a ZJ thing. If the ECM is cheap, try it. But I would be surprised if that is the issue.
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Re: 4.0 issues

Post by ghcoe »

Running a FI out of gas is real hard on the fuel pump. You might have damaged the pump and even though you have gas, it might not be delivering fuel at the right PSI. I would test to verify that you are receiving proper fuel pressure at the fuel rail. I believe you can rent a tester at some auto stores.
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Re: 4.0 issues

Post by Cecil14 »

I can only speak to the '91-95 OBDI ECUs, but they're essentially all the same. There are some differences between manual/auto, A/C and non-A/C, etc, but that really only lights up the CEL; it will not prevent the vehicle from running. The original ECU I had in the truck was a '94, think I have a '93 one in there now and the spare behind my seat is a different year again.

Autozone states that their reman computers require additional programming (VIN and mileage) before they'll even ship them to you (nothing stocked at the store). I doubt you're using the rest of the electronics from the donor vehicle, so I kind of doubt there's anything there to tell the ECU whether it's in the original vehicle or not? It's going to see the sensors it needs, but that *should* be all it cares about, I would think?

This is why I stuck with an OBDI ECU.... :)


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Re: 4.0 issues

Post by Shagoneer »

Sorry between my Jon and baby I didn't get a have to mess with the dang thing in a few weeks.

So I ended up replacing the battery, terminals, and plugs. Then when I tried to start it, it cranked for a second, then fired, and immediately stumbled and died. So I tried again, and it would fire once or twice but never start.

Any ideas?
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Re: 4.0 issues

Post by Shagoneer »

More news.

After double checking all of ground I played around a bit more today. I got in cranked it for a second and it sputtered for a second and then started right up. I shifted it into neutral so I could look under the hood and it died. I got out to make sure all of my connections were still good, and there is 12 inches of brown liquid shooting out the air filter on the valve cover. Ocean it stopped erupting I investigated and found that the brown liquid was gas mixed with something (I'm assuming oil), while looking around under the hood I found that the has mixture shot up at least 6 feet.

Now I'm really in over my head.

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Cecil14
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Re: 4.0 issues

Post by Cecil14 »

Sounds like you might be pressurizing the crankcase? If you've got some blowby that would explain the gas (have to be a ton of blowby, though, dang). Is the PCV valve good and working? (it should rattle).


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tedlovesjeeps71
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Re: 4.0 issues

Post by tedlovesjeeps71 »

What's the number cast onto the cylinder head? You can locate it roughly between cylinder 3&4 on the driver's side. Pray it doesn't say 0331.


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Re: 4.0 issues

Post by Shagoneer »

It's 0630
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tedlovesjeeps71
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Re: 4.0 issues

Post by tedlovesjeeps71 »

Hmm... Looks an awful lot like a blown head gasket.
First thing I'd check are the ports from the valve cover to the intake manifold. That's part of your PCV system. The rear one especially likes to push carbon and can clog up the port on the intake. I can see where if it were restricted enough it could possibly cause pressure to build up. At least that's easy to check. Pull the vac lines and look.
From there you may need to do a pressure leak down test. It can tell if you have a blown head gasket or cracked head.


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Re: 4.0 issues

Post by Shagoneer »

A rebuild kit with new pistons, rings, and gaskets is only about $300 I may just pull it and rebuild the whole thing
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Re: 4.0 issues

Post by Shagoneer »

But before I do that I'll going to see if I can go the cheapo route and and use head gasket sealant.
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tedlovesjeeps71
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Re: 4.0 issues

Post by tedlovesjeeps71 »

Shagoneer wrote:But before I do that I'll going to see if I can go the cheapo route and and use head gasket sealant.
Imho, wasted money and only creates more to clean when it doesn't magically fix it. I'd highly suggest you verify what the issue is.
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Re: 4.0 issues

Post by Cecil14 »

At very least do a leak down test. You really only need to put a little air pressure in each cylinder, and you'll get a wealth of troubleshooting information. If you go for a full rebuild without known the problem, you're very likely to overlook the problem and be back at square one and a few $$$ less later.


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Re: 4.0 issues

Post by Shagoneer »

I'm doing a compression test tonight when I get off work. How do I do the leak down test.
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Re: 4.0 issues

Post by Shagoneer »

Just ran my compression test.
When I pulled my plugs numbers 2,3, and 5 were completely black, while 1,4, and 6 still looked brand new.

And here are the results of the test
1: 115
2: 145
3: 150
4: 149
5: 60
6: 130


So I know that number 5 is screwed. I read that they should be between 120 and 150 so all of the others aren't bad.
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tedlovesjeeps71
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Re: 4.0 issues

Post by tedlovesjeeps71 »

It's conceivable that all that milkshake yuck is keeping a valve from sealing which could result in a low compression reading. I'd still try a leak down test to see if you can hear where your compression is going.


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