hunterpeaks

Ignition is good, Fires with authority when cold.
I mean, it starts great and sounds great.
As soon as it gets hot, then you turn it off, you can't get it to turn back on.

What I have done:
1-Replaced Starter
2-Fuel pump tested and works perfectly
3-Fuel Pressure is in spec with and without vacuum.
4-Good new fuel.
5-Great spark
6-Checked Fuel Injectors-Great pattern
7-New DME relay installed.
8-Tried another coil
9-New Spark plugs.
10-Air boot intact and all vacuum leaks eliminated (that I know of)
11-Pulled Crank sensor cleaned it off.
12-Changed out the coolant temp sensor to new.
13-Throttle position switch changed out to new.

Could it be:
1) Knock Sensor?
2) Catalytic convertor issue? No rattles in it so far, so maybe not.
3) Could be a bad air flow meter?
4) Tested ignition voltage where it reaches the voltage getting to spark plug. 2-3,000 volts at idle, usually up a 10,000?

Question: What changes when the car gets hot? Why is heat changing something that is then preventing the car from being re-started?

Another clue: Struggles on Rev up. Doesn't smoke. Did backfire at the end of the exhaust. It does struggle you try to rev it up to 5000. I started it this morning and sounds like it's fixed itself. Let it run for 5 minutes, then come back and tried to rev it up and it struggles initially and then goes up to 5000. Turn it off and it won't start back up.

Thanks so much!
Hunter

thomasmryan

Check your leak down rate on the fuel pressure.

Even with a good pattern, one or more injectors may be dribbling the pressure off when you shut it down, loading that cylinder so a rich back fire in the exhaust. As an experiment, get some gloves and put some dry ice on the rail and see what happens.

V2Rocket

might be worth swapping with another AFM as a test.
difficult hot re-start can be a symptom of a bad air intake temperature sensor.

jhowell371

Don't forget a leaking fuel pressure regulator or dampener. Pull the vacuum lines and check them for fuel.

Jfrahm

Look at the plugs when it's not starting. Are they wet? Smell like gas? Black with soot?

hunterpeaks

Thanks for help. On that today. Another question: What are the symptoms of a failing knock sensor?

tempest411

​​​​​​​You do not have a knock sensor on that car that I am aware of.

V2Rocket

right, 1984 has no knock sensor.

EJZero1

As someone (hopefully) closing the loop on my own no start issue, I'm a proponent of starting with Clarks Garage to troubleshoot and narrow down the source of the problem. That, combined with the wealth of knowledge and helpful nature of this group, will surely help you track down the gremlins your looking for.

That said, I was tracking a hot hard-start issue a couple of years ago, and I believe the issue rested with a leaky injector described above. The issue resolved itself when I installed new injectors. Admittedly, there were other mods along with the new injectors (M-Tune installation), but I haven't had the issue resurface since.

hunterpeaks

Hmmm. Mine definitely has a knock sensor. Maybe my car has had an engine change? Who knows. Anyhow, what are symptoms of failing knock sensor? thanks.

931guru

If you look at the wiring diagram for an 84 944, there is no knock sensor.

If you look at the parts catalog for an 84 944, there is no knock sensor.

What is the part number of your DME? What is the part number of your airflow sensor? What is the engine number?

A picture might help.

V2Rocket

no 8-valve 2.5NA came with a knock sensor, in any year.
i dont think even the 2.7L got one.

factory fitment was only on the 944 turbo and the 16v cars...i wonder if your car has a short-block swap.

more confusing would be if the sensor were actually hooked up to something.

audi49

The most recent issue of Porsche Panorama (July) has two questions exactly related to this in the Tech Q&A section. I think you've covered (maybe?) their answers, but based on my quick read. Have you...
-fully ck'ed fuel pressure after turning car off. article says it should remain at 20 psi minimum for 1/2 hour.
-fuel pressure damper
-fuel pressure regulator
-check valve in the fuel pump
-fuel injectors leaking (remove fuel rail with injectors in place, place paper towels under injectors, power up fuel pump by using a jumper to fuse 34)
-DME temperature sensor on side of block
(I got the above from the magazine).
Good luck.

thomasmryan

Did you get a VDO temp sensor? I have gotten dud facet and FAE sensors over the years. You might compare the readings from Clark's.


If your pressure in the rail drops quickly, suspect the check valve at the pump.
If it bleeds down slow, I would send the injectors off to witch hunter.

Is your idle validation clicking at the throttle position sensor? It's good to have a slight amount of slack in the throttle cable and the sensor positioned correctly.

F18Rep

Yea, I would look that way too. The best way is to check your temp 2 sensor from from the DME, because if the sensor were bad/disconnected/open the engine would have symptoms similar to this. Good cold start but may not even run once warmed up. The only other symptom that goes with this is that the exhaust will stink (acrid) when warmed up.

I think there is also a temp sensor in your AFM for incoming air temp - I don't know much about it tho. And don't get confused with the separate temp sensor that is only for the gauge, it does nothing but the gauge....Bruce