Anothe 944 no start question/problem
Tony
problem. My 87 944na ran great for a couple of days, now won't start.
Specifically, the fuel injectors aren't spraying fuel. That's the problem in
a nut shell. Wondering if anyone experienced same problem.
Background: I have a great spark. Timing belts are good. Trying to fix the
intermittent stalling problem, I replaced the fuel pump, fuel filter, DME
relay, fuel pressure regulator, reference mark sensor, and coil. I even went
so far as to resolder the DME and refurbish the Air Flow Meter. With that
effort I thought I finally fixed the stalling problem. The car started right
up and ran better than ever for a couple of days. Yesterday morning it just
wouldn't start.
I have good spark and timing is ok. The problem is that fuel is not spraying
out of the injectors. I did a 30 second flow test and got plenty of fuel
with the new DME relay, old DME relay and by jumping pins 30 and 87. Fuel
pours out of the fuel rail which indicates that the fuel damper is working
(or at least not impeding the flow of fuel). I haven't taken a pressure test
since I'd don't have an 11mm adapter, but with new fuel pump, filter, and
regulator, don't think that's the problem.
I have battery voltage at the injectors by testing with ground to engine,
chassie, and neg battery terminal. I placed a LED with 1k resistor across
injector terminal and can see it pulse. Resistance across injectors are in
specs as is the resistance on the reference mark and speed mark sensors,
I put a 9V battery across one injector and it actuates, but when hooked up
to fuel rail harness they don't. Like I said, I have great fuel flow through
the fuel damper. Since I have spark at the plugs; and voltage with pulse at
the injectors I don't think I screwed up the DME, but I don't know what else
to look at. Could one faulty injector cause the whole bank to shut down? I'm
totally frustrated. Has anyone had this same problem?
Tony
Hugh
I would say that you've done a good job of isolating the problem.
I'm inclined to first check if there is battery voltage on one of the pins to
the injectors. There should be because your DME is getting voltage as
illustrated in the coil firing. Note the coil gets it's primary voltage from
the ignition switch but the brain and the injectors gets it's voltage from the
DME relay's first set of contacts.
If there is voltage on the injectors then I would check the grounds between
the engine and the chassis and the battery.
Last it may be that the DME brain has died in the injector firing department.
This may be as simple as a bad solder joint or a driver transistor has blown
from high voltage from bad spark plug wires.
NOTE: Just because you have fuel flow does not mean you have pressure.
Hugh
PS: How is the timing belt?
Tony
Thanks for your input. I do have battery voltage at all injectors.
I checked the resistance among the negative battery terminal, chassie, and
engine in all combinantions an get low resistance (about 0.1 ohm) so it
looks like the grounds are good.
Timing belts are good and were adjusted about 4 months ago.
I also put a 9V battery across each injecter and can hear them clicking.
I've place a LED and 1K resistor on two of the injector connections and can
see the pulses. Hopefully this is telling me that the DME is still good.
(Even though I downloaded the DME schematics, I wouldn't have a clue as to
were to look for the injector drivers). As I was checking the LED pulse the
engine sounded as if it wanted to start. Leds me to think you may be right
on target with the pressure situation. I read somewhere that someone had
cracks in the fuel rail, not allow pressure to come up to specs.
I'm going to run out an get a fuel pressure gauge for more troubleshooting.
I just hope the new pressure regulator I just put in isn't faulty.
With the information above, I'd appreciate any other thoughts you may have
(or just in case it's not pressure related, the location of the DME injector
"department").
Dang! and the car was running so well, I even got around to finally fixing
my sunroof.
Thanks again for you most appreciated help.
Tony
"Hugh" <Hu...@ReallyBigCableCompany.net> wrote in message
news:3E79FBF1...@ReallyBigCableCompany.net...
Tony
I checked fuel pressure and fuel flow. Both are good as is the 20 minute
leak down test.
I'm now offically stumped. I connected four LEDs on across the the injector
connections and can see them all working while engine is cranking, The
injectors themselves spray when I connect a 9V battery across their
terminals. Looks like the DME is providing pulses to the injectors, maybe
it's just not enough voltage to trigger the injectors.
I don't think a voltmeter is quick enough to see the voltage change on the
injector connectors. Any idea on how to check this condition?
TIA
Tony
"Tony" <tzearste...@att.net> wrote in message
news:gLnea.19435$S%3.10...@bgtnsc04-news.ops.worldnet.att.net...
Hugh
One of the tricks is to disconnect one of the injectors and see if the car
starts on three cylinders. This is supposed to indicate that the fuel pressure
regulator is jammed and over pressuring the manifold.
Did you check the spark at a spark plug?
Use a spare spark plug laying on the intake or cam housing and connect one of
the spark plug wires to it. If you get a good spark and getting fuel it should
either start or backfire.
I'm still wondering about wither the timing belt is intact. Good consistent
spark at the end of a plug wire would tell if the cam is still rotating.
Two other things come to mind on the non-start. The AFS (air flow sensor) and
the throttle position switch (TPS). The TPS should click when you move the
throttle off of idle and them back again. The AFS uses regulated voltage from
the DME across a given resistance.
Wonder if the coil is weak?
Terminal 1 to 15 = 0.4 - 0.6 ohms
Terminal 1 to 4 = 5.0 - 7.2 ohms
Terminal 1 should have a green wire and comes from the DME
Terminal 15 is the other wire
Terminal 4 is the high voltage wire to the dist.
Hugh
Tony
Thanks for your input. Let me first start by answering your question then
restating the problem as I see it, because it's a real stumper for me.
1. Car won't start on three cylinders. That was happening when I had the
stalling problem which was corrected when I replaced the fuel pressure
regulator. Fuel pressure and flow is good now. I did extensive pressure
checks last night.
2. I have a good healty spark on all cylinders.
3. I when so far as to remove the front engine covers and the belts are in
good condition and rotating.
4. During the stalling phase I took the throttle body off and thoroughly
cleaned it (by the way, that helped restore a plugged vacuum port). The TPS
is correctly set and working. As for the Air Flow meter, I took it apart
and moved the wiper blades south to a virgin area of the ceramic resistor
wiper track. All voltage check are within specs.
5. I foolishly replace the old good coil with a new one. However the new
on is producing a good healthy spark.
With all that effort to correct the stalling problem, the car started and
ran better than it has in years. The problem started a couple of days later
when I went to start the car and it wouldn't.
To boil the problem down, the injectors aren't putting out fuel. None of
them. I see the DME pulse at the connectors, all of them (I connected 4
LEDs with 1K ohm resistors on each injector connector). I see a nice light
show when the engine cranks. There is plenty of fuel in the rail. As for
the injectors they do work when I connect a 9V battery. As a matter of fact
as a result of testing each injector with the battery, I squirted fuel into
the cylinders. The car would then start with that small amout of fuel, and
die when the fuel was burned off. The problem is, the injectors aren't
being triggered to spray by the DME but do spray with a separate voltage
sourse.
I'm thinking that even though the DME is sending a signal to the injectors,
maybe it's not enough to trigger them. But I don't know how to test that.
OR, I not sure what role the fuel pressure damper plays in this situation
other than dampening the pulsating fuel. If the damper is at fault, could
it prevent the injectors from pumping even with a good DME pulse and ample
fuel in the rail? I haven't seen much discussion on the damper and am
wonding what effect a faulty damper would produce. Do you know how to check
a damper?
My next step is to replace the damper and if that doesn't do it, start
looking at the computer even thought it seems to be working correctly.
thanks for your help
Tony
"Hugh" <Hu...@ReallyBigCableCompany.Net> wrote in message
news:3E7ABC44...@ReallyBigCableCompany.Net...
Hugh
The DME grounds the injectors thus any power is battery voltage to one
side. To check this you would have to use an o-silly-scope and check the
profile of the pulse.
Me thinks your DME has blown a transistor or two. This is not an
impossible home repair. Once you know which pins go to the injectors and
where they go to inside the DME box, you can trace the circuit down and
find the transistor(s). They are well marked so you can go down to Radio
Shack and buy a couple.
If you are not sure of this contact FR Wilks at www.frwilk.com.
He's quite a pro on the DME's.
This may just be one of the solder joints that has broken loose. I've
read threads where owners have opened their DME's and found the traces
scorched on the PC board!!!!
Another thought is that the reference sensor might NOT be sending a
clean signal but the DME will fire on anything that's at threshold
coming from it.
Check to see if the muffler is loose. Never know!!!
Hugh
Tony
Finally started and runs great.
I didn't want to think it was the DME, but I know you were right. My plan
was to trace the injectors to the DME pins and with the DME schematic, hunt
for possible faulty components. I took the computer out to study it against
the schematic and carefully cleaned the boards and contacts. I noticed a
couple of possible cold solder joints and touched them up. Before going any
further, I put the computer back in and it fired right up.
I suspect a cold solder joint increase resistance thus reducing current on
the Fuel Injection circuit. Apparently the DME was providing enough current
to activate the LEDs but not enough to fire the injectors. An O'scope
(which I don't have) might have told me that.
Other stuff just for background information:
I replace my faulty fuel pressure regulator that fixed my frustating
stalling problem. Recommend anyone with similar problem do a fuel pressure
check if the DME relay is working. I don't recommend just replacing parts
in hopes of fixing the problem.
I also resoldered by computer, thoroughly cleaned the throttle body (gunk
was restricting vacuum), and refurbished my Air Flow Meter with the
instructions obtained from www.frwilks.com.
This car runs better then it has in years.
I sincerely appreciate your help, you got me through a very frustrating time
by keeping me from staying from a methodical trouble shooting approach. You
da man!
v/r
Tony
"Hugh" <Hu...@ReallyBigCableCompany.Net> wrote in message
news:3E7B7DB6...@ReallyBigCableCompany.Net...
Hugh
electronic fuel injection system.
It's now your turn to pass on what you have learned Grasshopper!
I try to watch www.pelicanparts.com 944 board as much as this newsgroup.
Pelican has some great technical resources on the 944. There is also
www.clarks-garage.com. He has lots on the 944's.
Hugh
PS: $50 will get you an old o-silly-scope at most any electronics
surplus store.
jeri...@gmail.com
mbello...@gmail.com
Zarf
> I have a 1984 944 porche and the fuel solenoid keeps going out, can you help me with this issue
Unixnut
> I have a 1984 944 porche and the fuel solenoid keeps going out, can you help me with this issue
>
controls both the EMU and Fuel pump.