No Start Mystery

[SReppel]

Things are not making sense, Been troubleshooting this problem now for two weeks and still have not found the problem. I have read everything on Clarks Garage and ran tests on the fuel system.
The only way I can get the car to start just for a few seconds is to install the 3 wire jumper for the DME, pressure up the fuel rail, then shut the fuel pump off and crank the engine. The engine will start and idle for a few seconds. You can start the fuel pump for a second to keep it running but if you leave it plugged in the engine dies.

Here is what I have done so far to diagnose the problem:

Installed 3 wire jumper to run fuel pump
Ignition on, fuel pump running - 36 PSI
Fuel Pump off - 34 PSI
20 Minute leak down - pressure still 34 PSI
Vacuum system tested, - no Vacuum leaks
Injectors Tested - OK good Spray pattern - no leaking injector with fuel rail pressured up to 36 PSI
Swapped Fuel Pressure Regulators with one off another 944 - no change
Installed a clear hose on Fuel Pressure Regulator return line to the tank good flow observed while fuel pump is running and 36 PSI observed on gauge

Have also swapped the Computer with a know good one from a running car.

I am at a loss, has anyone had this issue. One of my PCA friends that lives next to me has 3 944's and had not seen this problem and he has been working on them and racing them for several years. We are both stumped.

My 944 is a NA 87 Model I purchase 2 months ago. It did have an after marked alarm system that I removed and reconnected all the wires that were cut and spliced into. Soldered everything and the car ran good for a couple of weeks.

Any ideas of what to check would be appreciated.

Thanks,

Scott
78 911 SC Targa Black
87 944 NA Black

[curtisr]

I'd try replacing the fuel injection relay.

[Dave Colangelo]

Sounds like it may be an electrical issue. Try cleaning up your grounds, fresh DME relay, Fresh injector relay, clean up the contacts on the fuel pump and all fuel system related items. I would also clean up the AFM and TPS sensors as well as the throttle body. These are often over looked and some times the issue in seemingly fuel related issues.

Regards
Dave

[iplagolf]

How strong is your spark? I was in Louisiana last year, had a no start, tried to start condition. I found a weak spark because the plugs were gapped too wide. The humidity was high enough when the engine sucked in the air it wetted the plugs just enough and then the fuel did the rest. I installed new plugs with the correct gap and haven't had a problem since. Remove a plug, put the plug wire back on, hold it to the block to ground it, have someone crank it over. Make sure you insulate yourself, plyers w/rubber coated handles or rubber gloves.

[SReppel]

Spark is good, I have a spark tester that I connect that I can watch when I crank the engine. I just installed a new set of plugs and gapped them also.

Getting ready to install another set of fuel injectors and try them. Seems like the injectors are letting too much fuel into the cylinders and flooding it out.

That is why I think that after I disconnect the power to the fuel pump it starts after cranking it over several times. Once the fuel is burner in the cylinders it shuts down.

If you pull the plugs after a no start (Fuel Pump Running 36 PSI on the rail) they are very wet with fuel.

Strange thing is that when I tested them to see if they were leaking no drips or anything else was observed with 36 PSI on the rail. I had plastic cups under each injector to catch the fuel.

Spray pattern looked good when cranking the engine, but I did not have anything to measure the CC's they were letting through.

We'll see tomorrow when I install that other set of injectors.

[SReppel]

Installed a another set of fuel injectors, still no start with the fuel pump running.
Removed AFM to test it. Don't really think that is the problem but may as well test it.

At a loss right now, discussed my issue with some of the other local PCA members last night at dinner and they didn't have any answers either.

I guess I'll have to start checking the voltages etc. going to the pins on the Computer.

[Phantoms]

If that doesn't work, I would contact the Hardy Boys, they haven't failed to solve a mystery from what I've read.

[curtisr]

Originally Posted by phantoms

if that doesn't work, i would contact the hardy boys, they haven't failed to solve a mystery from what i've read.

+1

[DannoXYZ]

Originally Posted by SReppel

Installed a another set of fuel injectors, still no start with the fuel pump running.
Removed AFM to test it. Don't really think that is the problem but may as well test it.

At a loss right now, discussed my issue with some of the other local PCA members last night at dinner and they didn't have any answers either.

I guess I'll have to start checking the voltages etc. going to the pins on the Computer.

How did you test AFM? Measure output-pin signal and manually open flapper door and confirm output-voltage increases smoothly with no dropouts? If you haven't, bend the wiper-arm to sweep over an unused portion of the resistor tracks.

Then hook everything back up and do your fuel-pump jumper trick to prime it. Then measure +voltage at pin-7 of DME-connector and start the car. This is the AFM-output and it should be around 0.75-0.90v at 950rpm idle. You want to measure at the computer itself to make sure the wiring from the AFM to the DME is working.

[SReppel]

I plan on hooking my AFM into my Buddys car that lives next to me. If it starts and runs then it's not the problem. Then I will do the voltage checks to the DME pins.
Glad he lives next to me, he has tons of parts and cars. He's having issues with one of his 944's also, got to hold the throttle to the floor for it to start.

We'll figure it out sooner or later.............

Hardy Boys, that's a good one. but we have all come across issues that sometimes are hard to figure out. Nothing is easy and it takes time to troubleshoot the problem.

[Phantoms]

Originally Posted by SReppel

Hardy Boys, that's a good one. but we have all come across issues that sometimes are hard to figure out. Nothing is easy and it takes time to troubleshoot the problem.

It wasn't meant to offend, just poking fun at your title. My car recently sat for a month and a half with an alarm related no start mystery, so I feel your pain. Best of luck with the troubleshooting.

[mytrplseven]

It sounds to me that spark isn't the issue if the car did run. I'm getting the impression that fuel is the problem. Even though you got good pressure, do you have good delivery of GOOD fuel? I'm thinking a plugged fuel filter, fuel strainer at the output of the tank (before the fuel pump) or possibly a kinked or plugged fuel line to the pump. Have you checked the fuel pressure regulator or damper for fuel smell in the vacuum line side?

[SReppel]

Well AFM is good so that is not the problem.
Last night I was thinking about the problem, got fuel, spark, everything seems to be okay and it will start after cranking it with the fuel pump off. I have been able to keep it running every now and then but it does not rev up when opening the throttle.

Then I had a thought , the dam catalytic converter could be plugged and it could be why the motor basically floods out with the fuel pump running.

I've had this happen to me twice before with cars I have owned. So it may be the problem.
I was going to remove it anyways so, I'm going to remove it this afternoon and see if it could be the problem.

Phantoms, no offense taken by the Hardy Boys comment. Sometimes ya got to have a laugh at some of the problems we have trying to keep these old cars running.

Scott

[TibetanT]

Scott:

Just a thought, are your reference and speed sensors pretty new? May want to check their respective connections to see if it is coming loose...sometimes this causes grief.
Fuel pressure seems a little high at 36lbs, so check your oil dip stick to ensure no gas is making pass the rings...Safety first.

GL

[SReppel]

Well, here is the latest; Removed the Catalytic converter (I was going to do it anyways) and it did not make any difference. It was not plugged as I had suspected. Same symptoms when trying to start the engine.

So I though what next!! I decided to pinch off the short fuel line going into the rail
to restrict the flow and pressure.

I installed the fuel pressure Guage on the rail and pressured it up before pinching the line. 36 PSI observed on the Gauge.

Cranked the engine with the fuel pump off and started the engine. Engine started and the pressure on the Gauge went to 0 PSI. Engine ran until it died for lack of fuel, (Fuel pump unplugged)

Adjusted needle nose vice grips on Fuel hose until it was pinched off. Re-connected the fuel pump and pressure on Gauge went up to about 20 PSI.

Started engine and it ran for about a minute. Tightened vice grips again and then cranked engine. Engine started up and ran.

Pressure Gauge indication less than 20 PSI. I could speed the engine up and rev the engine. I let it idle for about 5 minutes.

So I guess the Fuel Pressure Regulator is definitely bad or it would seem like it is. Don't think the Fuel Damper has anything to do with it.

Strange thing is I installed a spare FPR that my Buddy had and it must have been bad also.

So have a new FPR on order. Once I get it and install it I'll update this post.


Scott

[SReppel]

Got the new FBR in and installed it this morning, looks like that was the problem.
Guess the one I got from my Buddy was bad also.

Found one other problem once the engine was able to run.
It was running smoothly and then started stumbling, my Buddy was there helping me with it and he started checking vacuum lines and electrical plugs.

Under the air intake between the Air Flow Sensor and Throttle body is the Y Connector. Looks like there may be a hairline crack in it. He moved it around a little and the engine smoothed out again.

I used my UltraProbe and it definitely found a Vacuum leak there somewhere.

Next week I'll remove the Plastic Y and check the rest of the hoses in the Vacuum system. On an earlier post I did someone mentioned this Y fitting. It may be it or a split hose.

Got to go to work for a week. I'll update what I find later.

Scott

[SReppel]

Well finally found the problem, it was the DME temperature sensor. Changed it out and it starts right up. I did find a few small vacuum leaks but nothing major.

I also changed out the Thermo fan switch. It was bad and the fans were running all the time.

After reading all the trouble shooting information I could find, I never really saw anything related to the DME temperature sensor as a possible problem with the fuel injection. Finally saw some information on Clark's Garage and also on Pelican when looking up the part.

The only reason I found it was because my Buddy was there helping me trouble shoot it and pointed out that it might be bad.

Oh well a lesson learned.

Now on to cleaning up the rest of the car and getting it ready for the DE at the end of November.

Scott
78 911 SC Targa
87 944 NA

[stuttgart46]

Thanks for posting. This is just something else to check off the list in the future.

[mytrplseven]

Verrrry interesting

[pfarah]

Scott,

Good job! Sometimes things just don't make sense. I've been slowly replacing every original sensor in the car because they can have an indirect effect on a different system. However; looking at the car holistically, everything ties together in some fashion. Working on these pre-scanner cars strengthens our critical thinking skills particularly when diagnosing fuel delivery, ignition, and electrical issues. I admit that this forum greatly assists in pointing us in the right direction (at least for me) when I'm scratching my head in confusion.