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Unread 09-10-2014, 10:59 AM   #1
DraytonBrowning
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94 yj ECU problems

I took my jeep to my mechanic and they diagnosed it with a bad ECU and told me I need a new one. I am used to doing my own work and I don't feel that they properly examined the issue..

Symptoms:
Popping in the exhaust, off timing, difficulty starting after sitting for a while and over all lack of power.

Right now I'm trying to decide whether or not to just suck it up and buy a new computer (If so where should I do that) or take it in to the local 4x4 shop to have them confirm my problem. Any advice would be helpful.

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Unread 09-10-2014, 11:14 AM   #2
mike134
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The most common ECU problems (bad capacitors) can be repaired without buying a new one. But there could be other causes for your problems.

If you could answer the following questions:
When you turn the key to the ON position, does your check engine light come on?
Does the starter turn the engine over every time, even when the engine won't start?
If you leave the key in the ON position for 10 minutes, will it start right up? or do you have to keep cranking it?
How do you know that your timing is off?
When was the last time you did a tune up, answer for each of the following: spark plugs, plug wires, distributor cap, air filter, fuel filter.
Do you have copper core spark plugs or platinum clad?


If this is a daily driver, you may want to pay the shop to do repairs quickly. But, if you have some time to run through the forum diagnostics, then we'll have you up and running in a couple days for very little money.
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Unread 09-10-2014, 05:42 PM   #3
laybackman
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Quote:
Originally Posted by DraytonBrowning View Post
I took my jeep to my mechanic and they diagnosed it with a bad ECU and told me I need a new one. I am used to doing my own work and I don't feel that they properly examined the issue..

Symptoms:
Popping in the exhaust, off timing, difficulty starting after sitting for a while and over all lack of power.

Right now I'm trying to decide whether or not to just suck it up and buy a new computer (If so where should I do that) or take it in to the local 4x4 shop to have them confirm my problem. Any advice would be helpful.
That sounds like a timing chain issue to me. It could be stretched or it jump timing chain. Did this bad performance begin when you started it up one day? These engine often jumped time when shutting down or when you hit thee skinny pedal to pass someone. Get a timing light on this engine and see what that tells you.

Or ask your mechanic to bring this engine up to Top Dead Center on the compression stroke..by hand. If he looks funny at you, get another mechanic, or come back and I'll try to lay that procedure out for you.


Do one thing at a time, and one thing only.
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Unread 09-10-2014, 07:01 PM   #4
DraytonBrowning
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Things that have been replaced within the last 2-3 months
Plugs (Platinum)
Wires
Distributor Cap
Rotor
Oil
Oil Filter
Fuel Filter
Air Filter

Check engine light always comes on when I turn the key, Starter always turns the engine over. It usually starts up just fine after its been running for a while, when it has been sitting for a while it will rev up to 3000 rpms and then drop and die. I have hooked it up to a timing light and the timing is all over the place.

I tested my MAP sensor today and it was giving me a consistent .9 volts below where it should be.
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Unread 09-10-2014, 07:32 PM   #5
laybackman
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Quote:
Originally Posted by DraytonBrowning View Post
Things that have been replaced within the last 2-3 months
Plugs (Platinum)
Wires
Distributor Cap
Rotor
Oil
Oil Filter
Fuel Filter
Air Filter

Check engine light always comes on when I turn the key, Starter always turns the engine over. It usually starts up just fine after its been running for a while, when it has been sitting for a while it will rev up to 3000 rpms and then drop and die. I have hooked it up to a timing light and the timing is all over the place.

I tested my MAP sensor today and it was giving me a consistent .9 volts below where it should be.
What does the timing light do at hot idle?

Here is how a 95YJ MAP is tested so this should work for you also;

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Unread 09-11-2014, 02:48 AM   #6
Mark05059
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your not really going to like to hear this but change the platnum plugs out for plain old copper truck plugs.
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Unread 09-11-2014, 06:44 AM   #7
Que89YJ
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Drayton you are not dealing with an ecu issue. We can walk you through troubleshooting it.
First place to start is always checking your codes. Do this and post what you get:
http://www.jeepforum.com/forum/f12/h...codes-1257145/
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Unread 09-11-2014, 10:52 PM   #8
DraytonBrowning
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Alright, So first off no codes at all. And would someone mind explaining what would be the issue with my plugs not being copper core?
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Unread 09-12-2014, 12:20 AM   #9
mike134
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Copper plugs are always better for performance, platinum plugs are for long life. The spark plugs on some engines (like the Buick Century or Pontiac Grand Prix) are too hard to get to, so they use platinum clad spark plugs that last over 100,000 miles. The old Jeep engine really likes the extra performance boost of the copper plugs. For a few bucks and 30 minutes of your time, you should change them back to the standard copper type.

The platinum plugs can cause sputtering or loss of power, but I don't think it would cause your off timing (that will probably be the result of a bad sensor).

It sounds like you have a few problems rather than just one. Start with the easy/cheap things and work your way up through the diagnostics suggested by Laybackman and Que.

Run the MAP sensor test posted by laybackman first, In between their suggestions while waiting for a response, I would say you should take care of the following maintenance issues which may help (since the vehicle has been sitting):
1.) look for vacuum leaks by spraying carb cleaner all around the vacuum hoses with the engine on. Listen for changes in engine rpm. Change any hoses that may be leaking (5-30 minutes)
2.) Clean the IAC and throttle body with carb cleaner (1 hour)
3.) Change the spark plugs to copper core as suggested above (~$10, 30 minutes)
4.) Borrow the fuel pressure gauge from autozone and do the pressure leak down test to see if it is causing your cold start problems. you should have 31 psi at idle and it should be above 20 psi after 30 minutes. (40 minutes). While you have the pressure gauge, check your fuel pressure when you disconnect the vacuum line from the fuel pressure regulator, it should read 40 psi (1 minute).
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Unread 09-12-2014, 06:32 AM   #10
Que89YJ
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No codes at all now? No cel? Are you still getting spark?
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Unread 09-12-2014, 05:07 PM   #11
The_Goob
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Quote:
Originally Posted by Mark05059 View Post
your not really going to like to hear this but change the platnum plugs out for plain old copper truck plugs.
Yeah these ole Yj's dont like them fancy smancy platinum or multi electrode plugs. champion coppers for the win
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Unread 10-22-2014, 02:11 PM   #12
DraytonBrowning
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Quote:
Originally Posted by laybackman View Post

That sounds like a timing chain issue to me. It could be stretched or it jump timing chain. Did this bad performance begin when you started it up one day? These engine often jumped time when shutting down or when you hit thee skinny pedal to pass someone. Get a timing light on this engine and see what that tells you.

Or ask your mechanic to bring this engine up to Top Dead Center on the compression stroke..by hand. If he looks funny at you, get another mechanic, or come back and I'll try to lay that procedure out for you.

Do one thing at a time, and one thing only.
So it did in fact end up being the timing chain. Just put a new one in myself and things are back to normal
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Unread 10-22-2014, 04:38 PM   #13
laybackman
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Quote:
Originally Posted by DraytonBrowning View Post
So it did in fact end up being the timing chain. Just put a new one in myself and things are back to normal



That was my best guess based upon the symptoms.
__________________
Chicks dig me.....Fish fear me

Getting older, I have developed some special skills. I have the ability to cough, sneeze, fart and pee at the same time.

"If we cannot afford to take care of Veterans, then we should stop making them."
David C. Wilker Jr. USAF (RET)
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