IMRC vacuum leak?

[WZL 96]

Hey guys, I recently did a COP Swap on my 96 Cobra, I got it back together and it ran fine for a while, (500 miles or so) without the first issue, Then it threw a check engine light which turned up to be a PO171 lean bank 1. I smoke tested it and cannot find anything that I would have changed during the swap, however I did see some smoke coming from around the front of the driver's side IMRC (I think, hard to see in there).

If it was leaking there, wouldn't the lean code be on bank 2? the driver's side?

Has anyone had problems with their IMRC's leaking from either the shaft or the gasket to the head?

Could it just be a coincidence that it started leaking after the COP Swap?


Any input is appreciated guys, thanks,

 

[Martin6107]

Each shaft holding the butterfly valves contains a small o-ring on each end that creates a seal between the shaft and a bearing that is pressed into the actual IMRC. It does not take long at all for the o-rings to dry up and begin to leak. Thankfully, it is fairly easy to replace the (4) o-rings and (4) bearings for around $30.

Summary ...

http://www.svtperformance.com/forum...-the-motor&p=14606887&highlight=#post14606887

 

[mwolson]

The PCM bases the bank AFR on the time between the combustion event and the time it takes the exhaust to get to the O2 sensor. The value in the tune is called O2_Transport_Delay_In_Revs. If you have long tubes and have not changed that value, it will definitely screw up the PCM. Even if you have the stock exhaust, the PCM may not have the delay set exactly correct for your engine. It is not too surprising to me that it got the bank wrong.

 

[fastferndog]

Both great info!! The problem is very likely the IMRC seals/bushings, mark 8's are notorious for these, I'm surprised more cobras don't have the same problem.

 

[WZL 96]

Okay guys just an update,

I replaced all the PCV/Breather seals on the valve covers because i noticed if i sprayed water on them, it sucked it right up. New valve cover grommets, nice and tight, still a huge leak somewhere. I have quadruple checked everything I could have changed during the swap and I don't think its there.

I grabbed some starting fluid and just started spraying the engine in certain places, when I spray the front of either IMRC, the engine spits and gets all kinds of pissed off. This and the smoke test results earlier leads me to believe that it is indeed the seals on the IMRC shafts.

I will grab some new gaskets (are the IMRC-to-Head gaskets still hard to find?), and also some o-rings for the shafts and report my findings whenever I find the time to work on her. Just frustrating because I was planning on taking her to a show this weekend.

 

[Martin6107]

You may as well replace the bearings. Each engine I have torn down had one or more frozen shaft bearings.

 

[WZL 96]

Yeah, if that's the route I go I will do that.

I may run IMRC deletes though

 

[Tickle]

Have you had the intake off at all?

The reason I ask is I had a bad vacuum leak where I didn't use loctite on the center intake bolts and they came loose and caused it.

 

[WZL 96]

Yeah, I've had the same problem when I cleaned the IMRCs about three years ago. I doubt it's tat but it'll be the first thing I check on the tear down.

 

[bumsoil]

delete them..... i tried for almost 2 years to get rid of the vac leaks from my IMRC's. replacing them completely too. now they are deleted and my car runs SO good.

 

[Tickle]

I also recommend deletes. I don't worry about it anymore. No more codes or cleaning.

 

[Mindgame]

I deleted mine not too long ago. Worth it imo

 

[WZL 96]

Update!!!

Okay guys, just an update, I definitely found the problem! Martin, you were right, The bearings/O-rings at the ends of the IMRC's are leaking. If you look at the photo below, you can see one of the bearings in question. I stood the IMRC upright like in the photo, and filled that tiny little well with water. Then I started working the IMRC's open and closed, careful to not spill the water. Within only a few seconds all of the water started draining down the IMRC shafts on the inside. If water not under pressure will leak like this I can only imagine what air will do under negative pressure.

IMRC delete plates and gaskets from MMR are going to be ordered ASAP. Then getting a tune.

 

[CzchMex]

Did you have speratic idle at all? I found a video of a guy on YouTube that has the same issue as me. If you revved the engine the idle would hang. Then around 5 seconds later it would drop. Then sometimes during coasting with the clutch in the idle would bounce. He related it to IMRC leaks.

Did you have any of these problems?

 

[WZL 96]

Sometimes the idle would hang and sometimes it wouldn't. Ive been hunting vacuum leaks for quite a while now and I think by getting rid of tiny vacuum leaks here and there it found the next weakest link which was the IMRC's.

Even at low idle you could tell that it wasn't happy. It would stumble every 5-10 seconds or so.

I believe my little water test mentioned above revealed a huge leak on both sides. I can't wait till the deletes get here to go back together

 

[Tickle]

Did you have speratic idle at all? I found a video of a guy on YouTube that has the same issue as me. If you revved the engine the idle would hang. Then around 5 seconds later it would drop. Then sometimes during coasting with the clutch in the idle would bounce. He related it to IMRC leaks.

Did you have any of these problems?

I believe this is normal behavior while coasting to provide additional power for the brakes, etc. If it sticks too much it could be IAC or TPS related.

 

[Mindgame]

Big ups to MMR. That's what I did.

 

[WZL 96]

Deletes in, New Code

I installed the IMRC deletes from MMR and fired it up, took about 20 seconds for the computer to figure out what was going on before it idled smoothly. Took it for a drive and pulls like a beast up top and runs decently under 3250. The car threw a light as expected but not the code I was looking for. The lean code I was having has not come back because there are no longer any IMRC shafts to leak. That's good!

The code it did throw is a p0122 TPS low circuit input. I assume this is related to the IMRC deletes but do not know how. Has anyone else gotten this code after IMRC deletes? The TPS connector has a broken tab but has been this way for years without the first problem, so I have pretty much ruled that out.

Any input is appreciated guys! Thanks!

 

[mwolson]

That DTC should not be caused by anything related to the IMRC delete other than the fact that you had to disconnect it to remove the intake. Try reseating the connector and clearing the DTC. I would not be happy with the broken tab. Things on the engine can vibrate loose if not locked down.

 

[WZL 96]

That DTC should not be caused by anything related to the IMRC delete other than the fact that you had to disconnect it to remove the intake. Try reseating the connector and clearing the DTC. I would not be happy with the broken tab. Things on the engine can vibrate loose if not locked down.

You were right, I plugged in my code scanner to look at the engine data while running and noticded the TPS was reading 0% at all pedal positions. Threw in a new TPS and now reads at believable percentages and no p0122 code.

That being said, it threw a new code.......:cuss: the new code is p1311. something to do with the B1S1 o2 sensor. I plugged in my trusty code scanner again and noticed that S1B1 sensor was reading much lower than the other 3. So, I assume that is just a bad o2 sensor, especially since I believe that both upstream sensors are original. I bought a new sensor to replace it but I have not had time to put it in yet.