79 SC 3.0 CIS - stalling and hard start cycle.

[time260]

I need your help

My 1979 3.0 SC is hard starting and if starts will run for about 3 minutes and then shuts down. After few days (normally 3 days) it restarts or goes thru the hard start episode and if it starts, shuts down after 3 minutes. A vicious cycle.

Replaced were the ff:
fuel pump, ignition coil, distributor cap and rotor, battery checked good.

Question:
Electrical, fuel, or what others?

If so, which part and what test do I do to pin point problem part.

Thanks in advance

[longhornchris04]

Hopefully others (the experts if you will) will chime in. Based on my CIS homework (I have the same motor), I'd say its either:

1-bad ignition timing - unlikely but possible, and its easy to check, ensure your static timing is right before doing anything else
2-mixture is off - either too lean or too rich. Either way, during the warm-up phase its good enough to start, but once the warm-up cycle completes you end up out-of-range and she quits.

Is this recent, or old? When did it start? Any other clues?

Note to the experts - PLEASE CORRECT ME IF I SUGGEST SOMETHING DUMB. Most of this has been gathered from surfing the Pelican boards.

The right way to do this is to get CIS pressure gauges and the shop guide with the proper pressures. Without them its a crap shoot, but you should be able to get the engine going to get it to a mechanic who does.

If you don't have a pop-off valve in your airbox, stop now, get it towed to the mechanic. Without that valve you risk blowing the airbox... very expensive to replace.

There are several parts to CIS that work together to make the car start. On a cold start, the warm-up regulator (or control pressure regulator, same thing different name) keeps the control pressure low which results in a rich fuel mixture. As the engine temp rises (there's also an electric heater), the mix is leaned out to around stoich (slight rich). The 79 also had a vacuum element that provided full-throttle enrichment.

One way to check if you are rich or lean is to remove the air filter. On the right side of the airbox, by the fuel distributor, is the sensor plate. When running, this measures the air flowing into the motor. The higher it goes, the more fuel gets sent to the injectors. The counter-balance to this plate is the control pressure.

Ideally you should be able to do this with then engine at temp, but you make do with what you have. When running, if you carefully and gently lift the plate (ever so slightly, really just touch it) and the engine gets "better" you are lean. If you are rich it will stumble and die right away.

That will tell you if its lean or rich. What you do after that will depend on which. Let us know and we should be able to help further.

Either way if I were you, I'd get it running and limp to the nearest place with a CO meter and CP gauges to get a proper adjustment.

[jtfreels]

I had a very similar problem on my 82 it was the magnetic pickup coil inside the distributor, (connects to the green wire) I would get 655 ohms (or what ever) on the green wire. But after it ran for 5/10 minutes the engine would die, the green wire was "open" and it would not start till it cooled off.

Search Pelican for "green wire" for method of testing this. Test your green wire if "ok" then attempt to start, after it dies and wont start, test again see if it is open.

My blog (see the sig) has links to green wire info back here at Pelican.

Jay

[Paulporsche]

Not an expert; just a DF designer w/ one of these cars.

As Chris said, get those CPs and mixture checked. There are lots of threads on how to do this yourself, or take it to a mech who knows CIS.

Always, w/ CIS, you should make sure all your ignition components are up to spec first. Then check for vacuum leaks and check the CPs and mix.

[time260]

I really appreciate the fellow Pelicanites coming to my rescue - I will surely look into the suggestions above.

A bit of a background:

This started after the car was subjected to days of rain. It was park in a carport (rear end in) and to my surprise, the passenger cabin floor flooded (thru sunroof, soaked w > a gallon). That's when the cycle started. That was 5 mos ago.

Many months prior, I toyed with idle, mixture, etc - but did not give me any issues.

Also, I had a backfire at one time, where I had to re-glue the pop-off = vacuum leak, no start. I checked the pop-off yesterday and its intact.

Please keep it coming and again thanks....

[longhornchris04]

Any chance water got into the electrics up front and shorted something out up there. A short to any of the CIS components that use electrically heated bi-metalic strips would cause them to not function up properly.

If its the WUR, the end result is the WUR never leans out the mix and as the engine warms up the rich mix chokes out the engine.

A wiring diagram and a multi-meter could be used to check for power and resistance of the WUR, AAR and other CIS components that are powered. At least this could help isolate the problems. Paul's thread (all 9 pages of it) is probably a good read.

Also could be the issues that Jay mentioned, anything to do with electrics. Also, if you don't have it go here (http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_TOLbks_pg1.htm) and pick up the Bently Guide. While I haven't used mine as much as I'd like (and my car body is 75 so not everything is valid... still good for engine, trans, and most vehicle), its still an invaluable resource.

[psalt]

I need your help

I need a bit more information before any rational suggestions can be made. When it starts cold, how does it run and what is the idle speed ? What happens after it dies ? Does it refuse to restart ? Have you done the basic tests for spark and fuel after it dies ? Have you looked at one of the plugs? You can use a timing light or a spare plug and a clamp to test for spark after it dies, then check to see if the fuel pump runs when you lift the air flow sensor. Nothing really special happens after three minutes on a non lambda car, so a sudden loss of spark would be high on the list. If it stutters and stumbled a slow death and the plugs are wet from fuel, a leaking CSV is a possibility and checking the control pressure curve would be next.

[time260]

longhornchris04:
I will read Paul's 9 page thread on CIS. Do they include electrical values for CIS components?

psalt:
When and if it starts (cold); it starts normal, and responsive to gas pedal - but after a while it just shuts dead. No hesitation nor stuttering. It then refuses to restart until after days. Leaving green light on tach gauge lit and fuel pump hissing.
I will check: spark (your the 2nd to tell me) - what would cause loss of spark?

I will update of progress or resolution when fixed.

Really appreciate, thanks in advance.

[psalt]

When and if it starts (cold); it starts normal, and responsive to gas pedal - but after a while it just shuts dead. No hesitation nor stuttering. It then refuses to restart until after days. Leaving green light on tach gauge lit and fuel pump hissing.
I will check: spark (your the 2nd to tell me) - what would cause loss of spark?


The fuel pump should not be hissing (buzzing) after the engine stops. You may be hearing the CDI or your wiring is incorrect. Did you replace these parts in an attempt to fix this problem or before the problem started ? Any number of items can cause a loss of spark, CDI box, wiring, pick up, coil, rotor, cap, etc., you first need to determine if that is your problem, then diagnose from there. If you have a good spark, then put a DMV on the fuel pump terminals and watch what happens when the engine dies. What rpm is it turning when it dies ? How many seconds of cranking does it take for the initial cold start ?

[T77911S]

Originally Posted by psalt

Nothing really special happens after three minutes on a non lambda car,

paul, i disagree. the WUR is warming up and the CP is changing, or maybe it is not warming up and the CP is not changing, as it should be.

but, as paul said, i would check for spark since it is an easy check and will split the problem as to fuel or spark. pull a plug wire and put a spare plug in it and ground the plug to check for spark.

once it has died, with the key on, remove the air filter. on the left side, reach inside and gently raise the air sensor plate. there should be resistance felt immediately. as you raise it, you should hear a loud squeal as the injectors start to spray. if the sensor plate is easy to lift at first, the plunger is sticking.

you also have a vacuum controlled WUR and i think it has the thermo time valve (TTV). the TTV should open in about 20 seconds allowing vacuum to the WUR raising the CP to lean it out. you can bypass the TTV, but make sure you have vacuum on the the hose to the WUR. i believe the other end is connected on the rear of the throttle body near the bottom.

cant say i have ever heard of a TTS not heating up and turning off the CSV, but i suppose it is possible. might be worth a check

[time260]

Going back to my original question - to isolate:
Is it FUEL or Electrical?
Why?

How can CIS cause for sudden stall - no hesitation, no stutter, no chugging...?

Thanks.

[T77911S]

Originally Posted by time260

Going back to my original question - to isolate:
Is it FUEL or Electrical?
Why?

How can CIS cause for sudden stall - no hesitation, no stutter, no chugging...?

Thanks.

once it has died, try a spare plug on an ignition wire or connect a timing light to check for spark. that will isolate fuel/electrical.

does it gradually run worse or is it like turning off the ignition when it dies?

like i said above, the only things that have a time delay to them are the warm up reguator (WUR), themo time valve (TTV) and the thermo time switch (TTS) and the auxilary air regulator (AAR). not likely the AAR, you could put your foot on the gas to over come it being bad. the TTV has or should have about a 20 second delay. if it is not working, it could make the mixture about .8 bar richer. if you are already rich, it could keep it from starting once the engine warmed up. the TTV can easily be bypassed by connecting the vacuum line from the WUR directly to the throttle body.
the TTS could be bad. perhaps keeping the cold start valve (CSV) on. again, making it run rich and perhaps even flooding the motor. how fast it would happen, cant say. but i would think it would slowly start to run wosre until it would not run at all.
the WUR. it raises the control pressure (CP) as it warms up making the car run leaner. if there is no 12v to the WUR or it is bad, it will run rich as it warms up, eventually running too rich to run. but it should start to run worse as it warms up until it starts surging then dies.
the plunger could be stuck in the fuel distributor (FD). it runs fine cold, but again, as it warms it rns too rich.

an air leak. as it warms up, it leans out to the point it will not run.

[psalt]

Going back to my original question - to isolate:
Is it FUEL or Electrical?
Why?


You have to do some testing or all you will get are guesses and assumptions.