MCU?

Have a 88 yj with 4.2, standard.. Rins roughon cold start and excessive crank on hot start. Dealer service says metering pins are not moving in and out to regulate air and fuel.. Says the mechanic metered the MCU and it is faulty. New part is $800. Are they on the right track or are they trying to pull one? Trying to get ready for the ontario E-Test. Will it pass the e-test with out replacement?

Reply to
JEEPR
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New? It probably just needs rebuilt. Dealers charge way too much. $800 is a pure ripoff.

For example, the rebuild kit for a 72-90 Weber Carb (which I think is the one in your jeep) Please make sure before you buy any rebuild kit.

A full rebuilt carb from Napa is only $324

An OEM carb from chryslerpartsdirect.com is $251.10 The Factory overhaul kit is #30.38

Any decent mechanic can do the work for you and probably for $100 + parts.

Reply to
DougW

And actually with the current exchange rate those prices will be better. (I priced US$)

As for passing the e-test up in Ontario.. I don't have a clue. Might get by with some carb cleaner.

Reply to
DougW

in your jeep) Please make sure before you buy any

MCU = Microprocessor Control Unit. He's talking computer, not carb.

Reply to
bllsht

doh.

I got stuck on pins and fuel/air.

Isn't that the carb they do the nutter bypass on?

Either way, the ECM is US$294

And I still wonder if the metering pins are not a part of the cause as they can also stick.

Reply to
DougW

That's the one. Mike would know if the Nutter bypass is cool to do in Ontario. I would think so. Google "Nutter bypass".

Cheers,

Earle

Reply to
Earle Horton

The MCU could be toast. A used one at the wreckers is cheap. I would also try the 'Jeep' shops for a used one. 'DON'T' give any of them money up front though, none of them are reliable enough for that. I know too many horror stories first hand even.

The O2 sensor could also just be bad so the MCU has nothing to base changing the mix on....

Any number of sensors could have failed causing the MCU to go into 'limp home' mode.

The trouble is, they don't have a computer to tell them anything about it so have to shoot blind unless they really know 4.2's and their systems. There is a test block on the firewall for the sensors that needs a special 'Jeep' computer to read or knowledge with a multimeter.

Only one more E test too eh. Too bad it messed up just then.

The hard cold and hot starts could be as simple as having the gas filter in upside down. The filter has two outlets, you need to make sure the center outlet goes to the carb and the 'top' outlet goes to the return line. if the return line isn't up top, the gas siphons back to the tank when it sits and blows back to the tank on a hot shutdown effectively vapor locking it.

Where abouts in Ontario are you? If you are close to Toronto, I know how to double check the pins and the O2 and other sensors to see if there is anything happening there. I also can make them pass emissions, but I kill the computer doing it so it has to be manually tuned up. This is called the 'Nutter' bypass.

You also might want to just run it through the sniffer to see how far off passing emissions it now is.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Have a 88 yj with 4.2, standard.. Rins roughon cold start and excessive
Reply to
Mike Romain

Canadian Tire stores even have the carb kits for about $25.00. I'll put one in for $100.00 plus parts.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

These had the Carter BBD carb and are the ones folks do the bypass on.

I've never seen the pins stick, but have seen several problems with the stepper motor that moves the pins. The motor can stick or fail electrically. Most common failures are becomming stuck, or failing "open" electrically. Replacing the stepper motor will remedy this. Less common but more expensive is when the stepper motor shorts internally. This will take the driver in the MCU out with it.

Easy test with an ohm meter.

Reply to
bllsht

Even with an input causing only open loop operation, the pins should still move. It should also complete the initialization process when you crank the engine. That is driving the pins full rich, then back to the "centered" position. If it does this, you can pretty much eliminate a stepper motor circuit problem.

That special computer was pretty much just a fancy multimeter. It couldn't do anything you couldn't do faster with a multimeter and a handheld vacuum pump/gauge.

Reply to
bllsht

Thanks for the input!

Mike

bllsht wrote:

Reply to
Mike Romain

Well I bit the bullet and took it to crappy tire for the e-test and it failed 4 out of 5 test points.

I pretty sure the original mech. said the pins were not moving on start up.

Even with an input causing only open loop operation, the pins should still move. It should also complete the initialization process when you crank the engine. That is driving the pins full rich, then back to "centered" position. If it does this, you can pretty much eliminate a stepper motor circuit problem.

With that it could be the stepper motor? Or O2 sensor? Is there a way to activate the stepper motor to see if it works?

Mike

I'm in the Quinte area. Is there any where to buy a recondition MCU. The dealer looked for a used one but had no luck. I have looked on the net and can send it to the states and have it reconditioned for $200 US, but that is a 14 day process barring custom delays.

Every solution breeds new problems..

0||||||0

MATT

Reply to
JEEPR

There are two shops I know of in Toronto that will sell long distance and likely have them used.

Well one is gone it would seem.. For the better.

Here are some:

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Too bad you are so far away. I normally pass by your place on my way camping over New Years, but don't think I will make it this year. We hit the bush up near Weslemkoon, Lingham Lake and Bon Echo Park area for a week usually in our Jeeps. We run the dual use logging/sled trails. See the photos in my sig line link. I bought my 'glass body from a gent named Brian just north of Kingston 8 years ago. He does fantastic work! Hmm, I wonder. Here is his last known email address, maybe he can hook you up? snipped-for-privacy@sympatico.ca Feel free to use my name please.

If you had someone comfortable setting up a carb and timing, your Jeep can be made to purr by disabling the emissions computer and just manually setting it up. That is a free 25% seat of the pants power boost raising the 'actual' top end to 4400 rpm and I am getting

11L/100km or about 23 mpg highway with mine.

Mine, as well as every one (more than half dozen) I have 'Nuttered' also passed Ontario emissions on the ASM 2525 test with my last numbers being: 589 NOx, 16 ppm HC and 0.11% CO. My CJ7 also doesn't need or have a Cat on it!

You just need to add two new wires and connect the orange and purple wires at the ignition module to the orange and purple at the distributor to put the computer out of your misery. You then manually set the carb mix screws with the stepper pins set in the center of their travel and set the timing because it will be off about 15 deg.

It really is that simple...

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Hope this helps,

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

If the stepper motor doesn't move on startup, it's not because of the O2. You can't actuate the stepper, but you can check resistance through it using a multimeter.

There are 5 pins on the stepper motor. 2 on the top row and 3 on the bottom. The center bottom pin receives 12v with the key on. Measure resistance from that pin to each of the other 4.

The spec is from 50 to 100 ohms. My experience has been that the good ones test right around 80 ohms. Over 100 means excessive resistance and replacing the stepper will likely fix that problem. Lower than 50 indicates a shorted condition and the MCU will be toast as well.

Again, my experience has been that the bad ones always test WAY high or WAY low (less than 5).

Reply to
bllsht

New rules, vehicles 1988 or newer have to be tested every 2 years.

Copy and paste.

1988 vehicles -- which require emissions tests in 2007 -- will need to be tested again in 2009 and every two years after that for registration renewal. Similarly, 1989 models will require testing in 2008 and every two years after that. As well, the requirement for a valid Drive Clean pass for ownership transfer will continue to apply to 1988 and newer models.

Loks like they are really trying to force us off the road.

Reply to
JEEPR

How would that be?

Reply to
aarcuda69062

The interesting thing is looking at the results from emissions tests in california from folks that did the nutter bypass. The emissions numbers were better than some new vehicles.

Reply to
DougW

When I was a full time mechanic, back in the 70s-80s, we figured pollution controls didn't do anything except hurt your performance. I guess we were right. Now though, the new stuff might be alright.

Saludos,

Earle

Reply to
Earle Horton

My numbers and a half dozen others I have done also are really good. Good enough my Jeep draws a crowd of mechanics when it gets tested.

My last numbers on the ASM 2525 test were 589 NOx, 16 ppm HC and 0.11% CO here in Canada.

That 'will' pass in California also. If the plumbing is just strategically blocked with ball bearings and left, no one can tell the difference in a visual inspection either.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

Because there isn't anyone left in the garages that knows how to work on them so they just toss things like an $800.00 MCU at it and just 'hope' it isn't a shorted sensor that took out the MCU in the freaking first place.

This get too expensive and folks junk them because most are borderline for being rusted out anyway.

I have actually fixed a mess of MCU's that were blown from a sensor or fuel pump even, short. Usually it's the input diode or resistor popped. If the board isn't sunk in rosin, parts can be changed.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

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