74 911 starts, runs a bit and then quits

[casor]

My 74 911 has been running great until today. About a 55 deg day, raised the cold start throttle lever, started it up and it quit about a second ("1001") later. Tried again of course and it would just crank. Went back to it maybe 10 mins later and did the same thing - started and quit. Went back later and now it just cranks.

During one of the interims, I checked for anything bent, broken, hanging off, leaking or missing. All OK. I checked the fuses both front and rear, all the wiring, the CIS connections and it all looked normal. A little scent of gas in the eng compartment, but nothing too strong. It was relatively easy to see all this stuff clearly as I had the eng out last year and fluffed up the entire eng compartment and eng auxiliaries.

The link is here to get an idea of what I did last yr.
2.7 Engine Rebuild

I am seeking out the gurus for a place to start here to diagnose this. I know elec/ign is always the weak link but I just don't think that's it. I would welcome all comments, but I am not wanting to suck the life out of you guys - I can do the work, just need an idea where to start and what common faults would be.

Thanks
Rob

[fanaudical]

First and foremost, do validate ignition is firing and roughly in time (even if you don't think this is the problem). I can't tell you how many times I've started chasing "CIS issues" that were really ignition issues.

After that:
- Check airbox for air leaks and verify no vacuum leaks in the vac lines.
- Verify hand throttle is really functioning and that cold-start switch is activating.
- Do a system pressure test and verify fuel pump is performing to spec.
- Verify and test control pressures for the WUR.

I usually find my cold start problems somewhere in these four items.

[casor]

Thank you for the comments, have been doing research on exactly how to do what you recommended. I need the pressure gauges and fittings - any recommendations on whose to get?

[ossiblue]

Originally Posted by fanaudical

First and foremost, do validate ignition is firing and roughly in time (even if you don't think this is the problem). I can't tell you how many times I've started chasing "CIS issues" that were really ignition issues.

After that:
- Check airbox for air leaks and verify no vacuum leaks in the vac lines.
- Verify hand throttle is really functioning and that cold-start switch is activating.
- Do a system pressure test and verify fuel pump is performing to spec.
- Verify and test control pressures for the WUR.

I usually find my cold start problems somewhere in these four items.

This is the place to start (no pun intended)^^, especially with the ignition.

On your 74, the fuel pump is not controlled by a relay so the pump should run as soon as the ignition key is turned to "run". Double check that the pump is continuing to run. Also, your cold start valve is controlled by a micro-switch on the throttle body that closes when the throttle lever is pulled up. Double check that the lever is actually activating the micro-switch. If you come down to checking fuel pressures, a 74 has a throttle by-pass line from the fuel distributor to the throttle body (unless that has been replaced by a PO.) As such, you need to connect your test gauge lines a little differently than in other CIS engines. Let us know if you get to that point. Finally, tell us the number (or post a picture) of your WUR.

[casor]

The WUR number is
0 438 140 004 and there is a separately cast number 086

[Joe Bob]

Fuel, spark, air. Ground plug and crank engine.
Look for spark....listen for whine of CDI box and fuel pump.

Shoot ether into intake while cranking. If it tries to start, it's fuel related. Clog, filter or crappy gas....

[casor]

I do hear the fuel pump running as soon as I turn the key. The micro switch on the side of the throttle body is in fact closing when the throttle lever is pulled up.

[boyt911sc]

Originally Posted by casor

The WUR number is
0 438 140 004 and there is a separately cast number 086

Rob,

Are you aware you got a different WUR? As long as it delivers the correct control pressures profile it would work. But never seen a -004 in a 911 engine until today. I am less than an hour away from you in case you need some assistance.

Tony

[casor]

I will double check the number tomorrow when I have more light as the car is covered o/s right now. I am certain the 004 is correct however. I don't know enough about these things right now to understand why this may be a factor, but the car has always run well, even before I had the top end done. Are you saying my WUR is supposed to be on a Chevy Minivan?

That is a very kind offer and if you want to "just take a drive" that would be fine with me. But, however, let me do some of the basic checks before I ring the "five alarm fire" bell.

For some background, the fuel filter and accum are brand new as are the intake boots and injector o rings and mounts. I doubt it is a vacuum leak since the possible offenders were first evaluated and then cleaned or replaced and then installed properly when I put all the crap on top of the eng. Plus a VL does not really happen overnight, unless something fails catastrophically, none of which has been noted upon inspection.

While I hate to "assume", the above narrows it down to the fuel pump, the FP relay and socket, the micro switch and the WUR. Certainly, their could be a clog but I want to electronically check this stuff first.

[boyt911sc]

Originally Posted by casor

I will double check the number tomorrow when I have more light as the car is covered o/s right now. I am certain the 004 is correct however. I don't know enough about these things right now to understand why this may be a factor, but the car has always run well, even before I had the top end done. Are you saying my WUR is supposed to be on a Chevy Minivan?

That is a very kind offer and if you want to "just take a drive" that would be fine with me. But, however, let me do some of the basic checks before I ring the "five alarm fire" bell.

For some background, the fuel filter and accum are brand new as are the intake boots and injector o rings and mounts. I doubt it is a vacuum leak since the possible offenders were first evaluated and then cleaned or replaced and then installed properly when I put all the crap on top of the eng. Plus a VL does not really happen overnight, unless something fails catastrophically, none of which has been noted upon inspection.

While I hate to "assume", the above narrows it down to the fuel pump, the FP relay and socket, the micro switch and the WUR. Certainly, their could be a clog but I want to electronically check this stuff first.

Rob,

Did you ask Bill Boys about this problem? I know him since he was working with Don Rosen Porsche at Conshohocken as a lead mechanic. Your WUR is not from a Chevy Mini Van but for a Lamborghini!!!!! You got an upgrade (kidding).

How did you know vacuum leak was not a factor? Have you done a pressure test?

Your '74 engine does not have a FP relay. The engine looks very nice and clean. Your first blunder was trusting Vertex. I was another unhappy customer too in 90's and completely avoided anything to do with them. I switched to Pelican Parts.

Tony

[casor]

Yes it was primarily my own fault for not doing proper due diligence on the car. Vertex simply capitalized on my stupidity. Especially egregious considering my "hands on" CFO background having a lot of MA exp where we would literally take companies apart before considering buying them. Piece by piece.

Bill did the eng work on the car but I have not asked him at this point. I like him, but he has gone from providing an hourly rate and a guestimate to just giving you "the number" - and only "the number" - at the end. Not my style. Sorry. I guess the playing field has narrowed so much that the guys left can do what they want. And cars are lined up at his shop.

Frankly, given this state of affairs, it would ultimately be cheaper and more convenient for me to simply start throwing parts out the window and sticking new ones in. It's not like I haven't taken anything apart before.

Never occurred to me that was no FP relay as on my 78 SC, the socket of which was a real culprit on getting that thing going. I probably would have ultimately discovered this but thanks for short circuiting the answer for me.

[Charles Freeborn]

Originally Posted by fanaudical

First and foremost, do validate ignition is firing and roughly in time (even if you don't think this is the problem). I can't tell you how many times I've started chasing "CIS issues" that were really ignition issues.

After that:
- Check airbox for air leaks and verify no vacuum leaks in the vac lines.
- Verify hand throttle is really functioning and that cold-start switch is activating.
- Do a system pressure test and verify fuel pump is performing to spec.
- Verify and test control pressures for the WUR.

I usually find my cold start problems somewhere in these four items.

ALL of this. Quick first pass is can you hear the fuel pump whine? Then, can you hear the CIS whine? If not there's where to start.

[casor]

Charles - thank you for chiming.

I can hear a steady, unwavering hum when I turn the key which I presume is the FP since you sit basically right above it. I have not activated the CIS by the traditional pushing down of the giant air plate for the simple reason that I have not taken anything off the car yet - even the air filter et al. Plus, for reasons that will go unnamed, my garage is a mess and the SC is sitting where the 74 needs to be. I need to push the 74 into where the SC is and cannot do alone. And the pugs have been absolutely no help whatsoever.

[ossiblue]

Originally Posted by casor

Charles - thank you for chiming.

I can hear a steady, unwavering hum when I turn the key which I presume is the FP since you sit basically right above it. I have not activated the CIS by the traditional pushing down of the giant air plate for the simple reason that I have not taken anything off the car yet - even the air filter et al. Plus, for reasons that will go unnamed, my garage is a mess and the SC is sitting where the 74 needs to be. I need to push the 74 into where the SC is and cannot do alone. And the pugs have been absolutely no help whatsoever.

Take a deep breath and reread all the responses once again. Your problem looks very much like an ignition issue, IMO--it came on suddenly, you get a brief firing of the engine followed by no firing at all. A short rest and the circumstances repeat.

Yes, your WUR is not correct as Tony pointed out, but the engine had run well prior to this so that is not likely an issue. Getting the engine started and running is the top priority right now.

Here's what you do know:
1. The fuel pump runs when the ignition switch is "on", and continues to run--normal for a 74.
2. You have some spark because you get a brief firing of the engine. That event, however, disappears and you get no firing at all. This raises suspicion about the spark/ignition circuit--CDI and distributor.
3. Continued cranking produces nothing but a gas smell in the engine compartment.

Don't get frustrated and throw parts at this. It will be solved and by you, if you choose to follow through. I'd suggest you begin with your confirmation that you have a strong and consistent spark. Here are a few questions you could answer for us that will help:

Do you hear a whine from the CDI box when the ignition is "on"? (The answer is not definitive, but no whine is more likely to indicate a problem.)

What brand of CDI box do you have--Bosch, Permatune, or other?

Do you get a strong spark from a spark plug that has been connected to one of the distributor leads and grounded to the engine? Is that spark consistent and does it appear when you have the "no start" symptoms?

Have you inspected the "green wire" from the CDI to distributor?

Do you still have points in the distributor? If so, have you checked the gap? If not, have you checked the "air gap" in the electronic set up?

Answering the above questions will help us and start you on a troubleshooting path that will eliminate possible areas of concern. Keep us posted.

Oh yeah, Pugs are notorious for being flakes in the auto repair department.

[casor]

I have an after market elec ign on the car. Thanks for the input and I completely agree that ign is the place to start - plan to do later today and will advise...

Thank you again
Rob

[Charles Freeborn]

You're on the right diagnostic path. Aftermarket ignition may be the culprit - is it the whole system (MSD, electronic breakers, etc) or just breakerless and original CDI box? If the Bosch CDI is still in place it will make a faint high pitched whine when you put your ear near it.
Rudimentary first steps is to check (read - wiggle) all the leads going into and out of the CDI, distributor, etc and look for loose or corroded connectors. If that all checks out you'll need to go deeper.
Yes, Pugs are pretty useless as helpers...

[casor]

I first want to thank all the gurus for taking the time to render their comments and recommendations. It is much appreciated.

OK.
So, I let the car sit from last Tues eve to Thursday eve with my "slow boat to China" trickle charger, thinking that I was going to need a full batt for the recommended testing etc. I also would have had nobody to help me push the car until Thurs when my buddy Stu comes over to work on his blown up Hodaka.

And now the reason for the post's heading....

We're about to push it around when I say, OK, what the heck, let's try it just once more. Get in, stick to neutral, throttle lever, turn the key and the thing starts right up and idles normally w/o missing a beat. I let it sit for about 3-5 mins just idling. Sounds great, still not missing a beat. Turn it off.

What the heck?
Rob

[manbridge 74]

Make sure the wire's copper section from CDI to distributor is not touching the coaxial part (unsheathed metal section) or any metal. No spark condition if this is grounded.