New finding on an old problem...

jwmc1 · jwmc1's Garage

My car has not been starting, although it is getting spark.

Last night I decided to bleed the CIS system and little and make sure it was still spraying gas in to the cylinders. I turned the car over and it started and run until the gas burned off, but would not stay started.

Tonight I took the air box cover off and pushed up on the sensor plate while my son turned the car over, and I was able to get the car to run, although it was backfiring into the air box a little.

What could be causing the sensor plate not to move as it should and what could be causing the backfiring?

Thanks

ianc · 10-06-2005, 04:41 PM

If you remove the airbox cover and have someone crank the motor, does the sensor plate actually not deflect? When you move it by hand, is excessive force required? Does the motion feel smooth throughout the range of travel? Is the plate hanging up in the venturi?

ianc

Oh Haha · 10-06-2005, 06:04 PM

Jeez, didn't you just get this back from the shop?! Can they enlighten you as to maybe something they did?
Did you check the idle screw? I know it sounds stupid but we all miss the obvious sometimes.

jwmc1 · jwmc1's Garage

when the throttle body moves the sensor plate should as well, correct?

jwmc1 · jwmc1's Garage

Quote:

Originally posted by ianc
If you remove the airbox cover and have someone crank the motor, does the sensor plate actually not deflect? When you move it by hand, is excessive force required? Does the motion feel smooth throughout the range of travel? Is the plate hanging up in the venturi?

ianc

When I crank the engine it does not move.

aturboman · 10-06-2005, 07:39 PM

The sensor plate only moves when the engine is running. It responds to the air flow going into the engine. Lifting the plate with the key on will cause the injectors to fire and squirt fuel into the cylinders, thats why it started and ran briefly. You probably have something in your cold start circuit that's not working correctly. There is an electronic injector and air bypass valves that need to operate when the enigne is started cold. They provide sufficient air and fuel until the engine "catches" then the sensor plate moves and the main system comes into operation. Start by checking that the cold start valve fires when the engine is cranked cold. Good luck.

ianc · 10-06-2005, 08:16 PM

Quote:

The sensor plate only moves when the engine is running.

Totally wrong. The sensor plate deflects during cranking as well. Just think about it; you're sucking air in whenever the engine is spinning, right? And it is definitely spinning and sucking in air while cranking.

If the sensor plate does not deflect while you're cranking the engine over, then there is a problem. I'll ask again; is there excessive force required to deflect the plate? If not, then you probably have a huge vacuum leak downstream of the sensor plate that is allowing unmetered air to bypass it; hence no fuel is being injected and the engine won't run. This would be consistent with your having the engine run when you manually lift the plate.

ianc

jwmc1 · jwmc1's Garage

thanks ianc, I will have to investigate this weekend...could the leak also explain the backfire I felt when I manually deflected the plate? Also, no there is no resistance when I push the plate.

Paulporsche · 10-07-2005, 05:51 AM

The plunger has to move too, not just the sensor plate. There is a lot of info on CIS hard starting. You have to search. Your cold control pressure might be too high, giving you a lean mixture @ start. Search the Warmup Regulator (WUR). Your Aux Air Regulator (AAR) could also be defective. If the car starts, then the Cold Start Valve is probably OK.

john walker's workshop · 10-07-2005, 07:15 AM

unplug the sensor plate switch and see if that helps. spitting and popping after it starts is typical of a very lean condition. the warmup regulator may be causing this, but before doing anything to it, adjust the hot idle mixture to 3.5% first. if the hot idle mix is way off, the WUR in turn will be affected through it's warmup period. the sensor plate does move when cranking. not a lot though, so you might not notice by watching the arm through the airbox passage. be sure the big rubber boot on top is not split or not clamped completely. look inside the airbox for any screws that are out, or 1/2 way out, indicating a split airbox.

jwmc1 · jwmc1's Garage

Thanks, the sensor plate switch plug is behind the CIS unit to the right correct when standing at the rear of the car, correct?

aturboman · 10-07-2005, 08:57 AM

Ianc, I can tell you on my 2.7 when cranking the engine you could see no visible movement of the sensor plate until the engine started to catch. I made a speical sensor boot with a clear window to obseve its movement. So saying is "totally wrong" is a bit of an overstatement. I'll agree with you if the engine cranked long and fast enough I'm sure the plate would move since an engine is nothing but an air pump. I've always found on CIS that if the cold start circuit works correcly then these engines fire pretty quickly and without much cranking. I'd start with the basics, cold control pressures, cold start valve & wiring and thermo switch readings, also as suggested looking for "air" leaks in the system. The factory book is has a good fault tree for diagnosing these types of faults.

ianc · 10-07-2005, 09:15 AM

Aturboman,

Yes, you'd have huge difficulties trying to start if the CSV isn't working; it will probably not fire at all. The sensor plate may not appear to move very much when cranking, but it will move; it can't help but move since air is being drawn past it. When it moves, the injectors begin to flow gas, which will keep the engine running if it has caught sufficiently from the initial charge injected by the CSV.

From jwmc1's original posts, where he says he can make the engine run by manually moving the plate, and the fact that it pops and backfires, it sounds like like it's very lean, which could indicate a poor initial mixture, due either to insufficient cold control pressure, or a huge vacuum leak allowing unmetered air past the plate.

ianc

jwmc1 · jwmc1's Garage

I appreciate all of the input...time to hit the garage!

aturboman · 10-07-2005, 10:50 AM

Ianc I agree with you completely. I think he needs to check the basics as you suggested. I wonder if this engine recently ran fine and if there were any other symptoms leading up to this condition. We've all seen the "a new air filter was just installed and now it won't run" scenario. Jwmc1 has any other work been done recently? Let us know what you find.

jwmc1 · jwmc1's Garage

a lot of electrical work was completed and the car was running fairly rich. The engine was running very strong though...I have searched amd cannot find a vacuum leak. I tricked it into runn by propping open that sensor plate. There seems to be the right amount of resistence when I push up on the arm that connects to the plate.

jwmc1 · jwmc1's Garage

It's too bad, because the engine runs sweet and strong. I originally had intended to perform and complete restore of the interior and ectewrior to look just like a Carrera 3.0. Unfortunately, I just don't have the time or money. Before I sent it out to be fixed I was thinking about selling it in pieces, that might be what I do.

jwmc1 · jwmc1's Garage

Oh Haha · 10-07-2005, 03:26 PM

Hey john,
I am sorry for your troubles. I was hoping it would be something simple.
I am just a few miles away but I am afraid I just can't think of anything you haven't tried. Hang in there.

jwmc1 · jwmc1's Garage

I am parting it out...I have already got about 15 items on ebay, I will wait on the engine and transmission for now, not sure what it is worth, it is nice