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[Hollis]

Well today was a very productive day. i got my engine bay sorta cleaned out. I'm working on getting ym car back to 100% so I can get rocket chip and my mbc  

Anyways after removing the hiddious heat shields to put my new o2 sensor in I found a terrible crack.. I mean its pretty bad imo. I think I have found the reason I'm running lean.. The reason I say I'm running lean is because.
1, My spark plugs were all white. Changed them today.
2. My car bogs out. Stutters and backfires.
3. I run semi hot.
4. Loss of power.


Now I think I'm going to pick up a a/f ratio gauge today. Do you guys think that will help me pinpoint this? Do you think a crack in my manifold were the o2 is, is sucking more air in and fooling the o2? Causing the ecu to push less air in??

[Colorado1]

Just read that Hollis. You may not like this idea but if you have to replace the whole manifold put some JB Weld on the crack-NO JUST checked- don't use on cats & exhaust manifolds. Wonder if VHF paint could seal it? Can be used & cured on engine.I'm gonna pull my heat shields off since your last post, but I have power & no backfiring. Were in the same place on getting it to run right first. I thought these got good gas mileage-I'm burning through it just test driving!

[Rocketman]

Can you get a picture of the crack?

Nearly every XR2 manifold is cracked. Usually its either a hairline crack or a heavy hairline crack... They don't really leak though. Look at the underside of your exhaust shield - is it clean? Some carbon would be normal, if its a bad crack it would be *covered* in carbon.

I've heard a lot of people talk about air getting sucked into a manifold thru a crack. Think about this-
A.)Exhuast systems have "backpressure" i emphasize 'pressure'  as in positive pressure in the system.
B.) In order to generate boost on the cold side...that much pressure or more must be generated in the exhaust side...IE 10 psi on the coldside needs 10psi on the hotside, just an instance here not actual numbers

Point being air isn't going to get sucked into the manifold being that its a mostly positive pressure system

I'd do some heavy searching for vac leaks, A/F guage might help but its still narrowband and wont tell you *how* rich or lean you are running, just one side of the board or the other.

My $0.02
-Matt

[Colorado1]

That didn't take long. Heatshield is off and sure enough there's a crack running from the top of the O2 to the right side of the center bolt. Hairline on mine & stops about 1/2"+  before all the way through. Good call Hollis. No carbon on shield.

[Hollis]

Mine is bad IMO. The little bad that connects across it is cracked open. and its a pretty deep crack. I got a pic I'll have to load it. I just threw 100 bucks into it today. I hope its just a vac leak. But if I cant find ne thing I'm going to get a new dizzy and wires.

Anyways today it seemed outta timing. Its backfiring like crazy again. Feels a little weak. and it is PUSHING tons of oil out my breather.. Possibly a bad pcv valve?? I went threw 2qt oil in 80 miles tonight. All over my brand new painted valve cover. >.<

[Colorado1]

The bridge across mine is cracked also but that's more of a structural part. I've been trying to figure out how to put pictures up to compare but not sure how. I'm gonna make sure you can contact me by email if you want & I'll get pics sent back. I did find a XR2 in a junk yard but not too close. They just hauled the one close off. Would've cost less than $30.00 to pull.

[Rocketman]

Hollis what was your compression like? Oil shooting out of the breather is usually indicative of very very low compression, when I melted pistons it was like a geyser. Check your PCV make sure its not clogged

[Colorado1]

Did a vaccuum test,first time so I hope I did it right-from the line nearest the TURBO label. Read constant 13 1/2 @ idle, constant 15 @ 2500 rpm's. Drops when throttled and regains to normal. Was that right & does it tell me anything? My guage also reads fuel pump pressure but don't know how to hook it up?

[Rocketman]

What is your car idling at? Thats awful low vacuum, should be 16" closer to 18/20 at idle

[Colorado1]

It idles @ 800

[Colorado1]

Well 800-850, I guess I hooked up to the right place. I posted somewhere that I thought the idle control screw was factory sealed but I can see mine-thought when they were sealed couldn't get to 'em that easy.

[Rocketman]

Wait on the top of the manifold? One of the lines that goes to the distributor?

Try on the side of the manifold, there should be an extra line capped over there. The lines on top only see a partial vacuum.

[Colorado1]

13 1/2 @ idle, 14 1/2 @ 2500?

[Colorado1]

That was going straight into the covered one, Teed off on the one below with red dashes gives me 13-idle & 14 2500.

[Colorado1]

The first one not on here went straight to the dist. & gave me 0 until some throttle, so I went to the other on top next, then just did the sides. I'm pretty sure the gauge isn't off- but should the dist. Be 0 @ idle anyway?