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IMRC Delete

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Posted by: Calabrio

What are the pros and cons of an IMRC delete on the Mark VIII?
I've heard that it opens up top end performance but at the expense of low-end. Does it hurt or help fuel economy?

And is there any way to rebuild a IMRC. I've mentioned in other threads, the bearings in mine are leaking air at the ends.

Posted by: driller

Naturally aspirated, you'll lose torque and drivability will suffer. Deletes work well with boost from what I have heard. I have no idea how fuel mileage would be affected.

Posted by: Calabrio

It's NA, so I guess that would be a good idea? Do you know of a way to rebuild them? Is there an aftermarket kit that will replace the o-rings and bearings on the butterfly valve? I have a '93 with the vacuum activated butterflys

As mentioned, mine is leaking from the back.

Posted by: driller

Anything can be rebuilt.

They are sure to be just pressed in bushings with 'o'-ring seals? A small machine shop should be able to press out the bushings, and fab new ones. I would use Beryllium Copper as the material for the new bushings.

I cleaned up a set of IMRCs when I replaced my intake manifold and I don't appear to have any issues. I have a set of IMRCs in the storage shed. Next time I'm there, I'll investigate some more.

Posted by: Psychostang

Any more info on this? MY 96 IMRC's are also leaking

Posted by: buddylee

Quote:

Originally Posted by AHD

Any more info on this? MY 96 IMRC's are also leaking

what does run like?

Posted by: Calabrio

If you're asking how it runs when the IMRCs leak, I can try to explain it.

The problem is that unregulated air is entering the manifold. The car attempts to counter act this air by adding more fuel. So you end up with a situation where the car is dumping gasoline into the cylinder. Eventually this leads to a misfire. It sometimes causes a slight miss you can detect at idle, but when you're driving under load, you can really feel the misfire.

Eventually it becomes severe enough to actually be confused with bad wires, or an improperly locking torque converter.

It's very frustrating, it hurts local drive ability, and it wastes a lot of gas.

Posted by: 93' Blue on blue

If its un metered air surely a lean condition would exist? How would the engine computer know to add more fuel?

Posted by: Calabrio

Quote:

Originally Posted by 93' Blue on blue

If its un metered air surely a lean condition would exist? How would the engine computer know to add more fuel?

The same way you can plug in a scanner and read the air/fuel ratio. A lean condition does exist, then the computer increases the amount of fuel in the cylinder. It might actually end up still being too lean, my plugs never fouled, but it still spikes the fuel, and whether it's too much fuel or too much air, it misses.

Posted by: 93' Blue on blue

When you plug in a scanner you are reading the computer and what the computer 'sees' which uses info from the various sensors, like the MAF to calculate how much fuel/timing to use. What im getting at is that an air leak would bypass these sensors and the computer wouldnt know any different, a lean condition would occur and possibly cause the knock sensors to retard the timing. I dont see how the computer would 'know' that there was extra air in the cylinder due to the leak at that point. See what i mean? I believe you, just trying to get a better idea of how the engine works.

Posted by: 93' Blue on blue

I did forget one set of sensors! the O2's. LOL. I think i answered my own questions!!! Im daft! lol.

Posted by: Psychostang

When I worked for a FLM dealership, I was able to use the IDS computer system to check my fuel trims. With all of the vacuum leaks, the long fuel trim was at 22/23% positive. When I removed the vacuum booster line, it went down to 12/13% positive. I still had a big leak. Now, that i've taken things apart, I found out that the drivers side imrc actuator was a major leak. My mityvac tool couldn't draw a vacuum on it at all. I've since repaired that down to a little leak, and just installed a new actuator on the right side.

The imrc plates have mini bearings, not bushings. The part number is 1680D. It is manufactured by NMB corp. Here is the p/n breakdown:
16 = outside dia. in mm
08 = bore dia. in mm
D = Single seal on each side.

While turning the drivers side, I noticed that the inner bore did not turn with the rod, I figured air was getting by the rod. I innitially thought that the rods were pressed in. When I removed the rods, I found a seal on both ends. It was hard and brittle. I used a pair of small dykes to cut them. They just broke apart. They were prolly carbon seals. I went to autozone, and purchased 4 orings, with a 9mm o/d - 5mm i/d - 4mm thickness. They were a tight fit in the bearings, and actually sliced off a little sliver of material. So now I have 4 custom fit o'rings. Hopefully that is where the leak was originating from. I'll let you know when I get it back together.

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