Starting to go mad!!

[Pritchard]

What a finicky little car we love!

I have a '74 2.0 L w/ stock engine except for Pertronix ignition. I have been working on this engine for about ten months now. It has come a long way w/ all the help I've received from PP and the BBS. What makes me so mad is that just when it seems that the engine is finally running about perfect, something else will go wrong. The latest problem is this. Suddenly (ran great before lunch, terrible after lunch), the engine has this lean hunt at idle. It will hunt between 0 RPM and about 1200 RPM, sometimes dieing at stoplights. It runs like a dream when accelerating, just not at idle.

I know that this probably means a vacuum leak somewhere. I just can't find it. I have checked the AAR, manifold tube hoses, the nuts holding the manifold tubes to the heads, all vac. lines in engine compartment, vac. lines to the dizzy, the MPS holds vacuum, the throttle switch is functioning and set according to directions here at PP, the CHT is new and providing the correct resistance, fuel pressure is at 29 psi. I set the valve lash about 500 miles ago.

I'm going to check the seals on the injectors this weekend as well as the gasket under the intake air distributor.

I've read that not being able to balance the fuel mixture between idle and off idle could be caused by a faulty MPS. If this is the case, anyone out there around Burlington, NC willing to let me borrow their MPS to verify if this is the problem?

If anyone out there has any ideas on what could be the problem (other than the mechanic), please let me know. I'm about frustated enough to put carbs on the thing.

Thanks for any and all help!

Pritchard

[Germain]

Only thing I can help with is a quick way to find a vacuum leak. Start car. Take a can of carbon choke spray and spary the hoses, gaskets, and anything else that might leak. When the engine revs up, you've found your leak.

[Steve M]

In the event that it turns out that it isnt a vacum issue it sounds like something I had a while back.
My aux valve doesnt work at all and it seems that I dont have a use for it. That's closed all the time now. With that said here is my story.
My car used to jump from just under idle to about 1000-2000 rpm. First I adjusted the idle speed, then I fine tuned it with the little brain box. Once that was done and the engine warm, I set the timing. Then I turned to car off and started it up again, while it was still warm. If the car doesnt catch right away open up the idle screw a little. When my car is cold I have to keep my foot on the pedal until it warms up, thats because my aux valve closed and causes the combustion chamber to think that the engine is warm. I dont know if this helps any but its friday and I'm going crazy sitting here at work....I cant fall asleep or anything.


Oh yeah, if the MPS is faulty it will cause this also. Guess what I did with my brand new one when I bought it. I drilled out the rivets cleaned out that epoxied screw and now its adjustable. I put in long bolts and sealed it all up and that's that. Anyone can do it and I dont see where it would harm anything provided that you assembled it back the way its supposed to be.

[This message has been edited by Steve M (edited 09-29-2000).]

[greenwood]

have you checked your FI trigger points? I was having alot of hunting problems too; I switched out almost everything, but the trigger points were what made the most difference, then I just fine tuned the mix with the knob on the brain and now I'm at 900 at idle

Also I may be able to help with the MPS...I live in VA and i'm going to visit my mom in NC in a couple of weeks...I believe Burlington is sorta kinda on the way. I don't know if you can wait that long but I'd be willing to stop by and let you borrow mine for a couple of minutes...

jeremy

[JP Noonan]

MAke sure that the CHT wire or part of the tinware isn't stuck between the intake tubes and the head, I know you looked allready but it happened to me.

The injector seals go bad quite often, but I've never had one so bad it caused more than a high idle. If yours are completely gone I guess it would cause the problem.

MAke sure you have a 2.0L MPS, I mixed mine up with my 1.7L once and the car ran all over the place.

My 1.7L ran similarly when I forgot to plug the vac line into the MPS. If you have a decel valve try removing it from the loop.

With you it seems like the car did it by itself, so I would say something came unpluged. Or if you have a resistor inline between the CHT and the harness remove it, they can go bad.

[Pritchard]

Thanks for all the replies. I was way too busy this weekend to check for any vacuum leaks, maybe this PM. The CHT wires are all clear of any possible ways to short, the Aux. Air Valve seems to be working correctly. I am inclined to think that I have a vac. leak, bad trigger points, or the MPS is going bad.

About my MPS, a PO had fiddled with the car quite a bit before I bought it. I noticed last fall that the MPS had no "cap" screw, only the adjustment screw. This makes me think that maybe I have a MPS for a 1.7 instead of a 2.0. The adjustment screw is backed out all the way to flush w/ the housing allowing for a richer mixture, which is what the 2.0 would need as compared to a 1.7.
After reading Kjell's article and finding (mistakenly) that the resistance between two of the pins (misnumbered in article) was not what it was supposed to be, I tore into the MPS. I put it back together and it seemed to work fine until now (if it is indeed the problem).
All of this only matters if the MPS would SUDENNLY go bad, which seems not too likely. By the way, it will still hold a vacuum.

When I replaced the Vac. Adv. Unit on my distributor about a month ago, I cleaned up the trigger points and had a little trouble getting them centered so that I was getting a signal to both outside terminals when rotating the dizzy. I am guessing that these are the original trigger points (over 100,000 miles). Probably wouldn't hurt to replace them anyway.

Greenwood, thanks for your offer to let me borrow your MPS. I'll let you know if things don't improve over the course of this week.

JPNoonan, thanks for offering to mail me your extra MPS. If things don't work out with Greenwood, I'll take you up on that offer.

Thanks to all for your advice.

Pritchard

[Dave Bell]

Another trick for vacuum leaks. Apply RTV over any joints, connections or fittings that you suspect... heck you can even put it on areas you don't suspect. If you want to track down the leaky area, put it on, one place at a time to figure out what area was leaking.

Sometimes these connections/fittings look good, but they are not.

- Dave

[JP Noonan]

I agree, I used RTV on the intake hoses, and smeared the intire intake plenum seam. It seems that where the two halfs are welded together it starts to leak over time.

[Conrad W Peden]

All I gotta say is some of you guys must have an awful lot of RTV on your cars. It seems like every time something is going or gone bad it gets hit with RTV.

My 73's DPO's trick was electrical tape in place of hose clamps, nuff said.

[This message has been edited by Conrad W Peden (edited 10-02-2000).]

[Germain]

Pritchard, have you gone mad yet?¿?

If not, when you do this still applies.

I get his car because I'm my own favorite PP user

(hay if he's mad he can't reason)

[Pritchard]

Not that M A D yet!