Robbe

Hi all, after much reading over the last couple of years, but not posting, I now have a problem that I need some help with.
So here is my first posting, and my apologies for that it is a problem-posting...
So what 's the problem? Yesterday, when driving, and using boost, the car stopped with idling at the nearest junction.
I could start it again, and continue, but it would not idle anymore. So that was a "spirited" trip back home as you can imagine, with an engine stalling during driving (shifting) all the time, and backfiring when I would relase the clutch to get it going again (all under speed).
So today I am trying to find out what went wrong.
What m,akes it difficult is that this is a converted car, originally born as a 75S, but with a 3.3 turbo transplant, with all sorts of goodies like a huge intercooler and so on. But also with rather dodgy solutions electrically. Built as a 3.6 turbo lookalike, but I have been busy getting it back to 70's look.

As above 2000 rpm the engine sounds fine again, but terrible below, it must be connected to the idle circuit.
I have read all kinds of postings about stalling and bad starting etc, and tried to check a lot of things.
So here is what I have done already:
- relay clicks (and engages) when I turn the key
- all fuses checked.
- when the green connector is disconnected , pump starts to make a lot of noise, same thing when the metering plate is pushed down.
- when the car runs, disconnecting the white wire from the boost sensor stops the engine

But now for the funny part. When I use a screwdriver to open up the meteringplate just a mm, I can start the car without problems, and it will idle at 975 rpm. I can even rev it normally.
But when I remove the screwdriver (and the plate completely closes), the car stops to run right away, and will not start. Insert the non-standard metering help, and all is well...
So what can this be? Is the metering plate normally drawn down by vacuum , not anymore on mine, and thus the screwdriver is helping it back to normal position?
Or is this all just a coincidence?
Before I wil have to have it towed away to a dealer (do not want to drive it with the screwdriver of course), I hope for a simple solution...

mel_t_vin

Robbe, welcome to the active forums, with your first post after 5 years!

You are correct in your assessment that the CIS metering plate is drawn downward by vacuum [reciprocating pistons] and the engine's need for oxygen, based on RPM. Depending on the plate's deflection, the requisite amount of fuel is metered to each of the injectors [by the fuel head].

My understanding of CIS is that engine oxygen requirements at idle are not sufficient to deflect the metering plate, and as such, it remains closed. In order for the engine to idle properly, the system has an AAR, Auxiliary Air Regulator [930.606.102.03 for '78-'79, 930.606.102.00 for '86-'89], that basically routes the appropriate amount of air around the [closed] throttle body for proper idle. On a stock set up, the AAR is located below the air cleaner, behind and centered between the fan and a/c compressor, with a 15mm hose going to the right side of the intercooler, and another hose going to the intake manifold downstream of the throttle body.

While you could have another issue, I suspect your AAR is no longer functioning properly. Let us know what you find.

Robbe

Hi Allen,
thanks for explaining the CIS and metering plate. I have searched a lot, but could not find the answer to my question if the metering plate should allow air to pass on idle. But now I know that it should be closed, and my screwdriver is just a way of overruling other devices like an AAR and maybe the WUR.
I will look for the AAR, but as this is a fairly modified engine in a 70's shell, I could find any of the used AAr-types I suspect. But as I live in The Netherlands, and it is a euro car, I assume the newer type will be the one.
But I will look into that tonight, at least I have a clue now where to look.
Will keep you posted!
In the mean time, if anybody else would have another opinion, be welcome! Driving around with a non-standard meteringplate modification is not really an option, if somehow the AAR would turn out ok.

A question about the AAR: is it only for when the engine is cold? As the problem first occurred when the engine was fully warm. When the AAR is only a help for a cold engine, and not for a warm engine, the problem might lie somewhere else?
I also thought about a vacuum leak somewhere, but would that not just help the engine getting air? Which is what the AAR in fact also does?

The screwdriver solution lets air pass the metering plate, which than can function again in supplying fuel. Making me think that a vacuum leak would not be the cause, as combined with the screwdriver, it would get too much air, and then the engine would not have run as it should.

So I think the engine gets too little air below 2000 rpm, running too rich. Or is that a false assumption, and it in fact runs too lean because not enough air means not enough fuel?
Plugs were black when I checked them, but that could also be a result of me messing around with that screwdriver, as I checked the plugs halveway during my inspections...

Mark Houghton

Your screwdriver trick is opening up the ports in the fuel head more than they should normally be open at idle speed, with less air being drawn in commensurate with the fuel being delivered. Thus, it's causing a rich(er) condition. If that results in your idle stabilizing, then your base mixture adjustment is off. If this is a recent development, then you may have a small air leak somewhere which is causing a lean idle.

Try adjusting your mixture (see the picture, the spring loaded post to the right of the metering plate). Using a 3mm allen wrench, push down on the post until it just contacts the metering plate and turn it clockwise (you'll feel some resistance as it engages the internal adjusting mechanism). Turn it just a few degrees...it doesn't take much to have a big effect (keep track of how much you turned it so you can go back to where it was if needed).

Robbe

Thanks for a valuable explanation as well. Will try that. I was under the impression that the post alrady had its built-in allen key, but I understand that I have to insert one myself.

Any idea if the possible air leak is in the vacuum circuit (like to the dizzy) or in the pressurized circuit, so maybe a blown o-ring? Before I have to take all apart and will have to renew all o-rings because of that...

Mark Houghton

After re-reading your post, it seems likely you blew out an O'ring or some such seal while under boost. Now, at idle, with an air leak you would run lean because of the extra un-metered air being drawn in (which explains why pressing down on the metering plate makes the idle better). CIS operates sometimes directly opposite of what you might think. IF you have a bad seal somewhere in the intercooler connections, now when you raise your rpm's past idle and start building any amount of boost, some of that booster air will escape and cause a rich condition that gets progressively worse the harder you push the car. That will also explain why your plugs are all black and sooty.

If I were you, I would systematically check all connections before and after the turbo, through the Intercooler and where it connects to the intake manifold. Do all of that before messing with the mixture adjustment or you'll just end up chasing your tail.

Robbe

Solved!
And so right you were Mark!
I wanted to take off the intercooler, but before I undid the nuts, the just tried to wiggle it.
And I directly noticed more movement than I had expected.
After undoing all clamps to the silicone hoses on the left side and on the right side just below the window, I took it off.
And then the pipe to the throttle housing fell to the side. Hmmm, I did not undo that part!

What had happened over time was that the rear lid had often just touched the upper pipe, wiggling it loose (or looser).
With my latest drive I simply blew it off, or at least blew the gap larger.

Needless to say that I reinstalled everything, removed the screwdriver, et voila completely solved!

The metering plate just opens a tiny fraction when idleing, what I in fact replicated with the screwdriver trick...

Thanks all for thinking and responding.
I hope the next person with such symptoms finds this post and learns !

Mark Houghton

Most excellent!!! 9 times out of 10 it's something simple. The fun part is understanding how everything is supposed to work, and diagnosing from there becomes a bit easier.

MUSSBERGER

Nice job Mark.

mel_t_vin

Well done!

Happy motoring...