Got stranded last night
11-06-2013, 04:37 PM
#16
Instructor
With my '86 944 and '86 951, I've had episodes with TPS, fuel pump, reference sensors, catalyst, O2 sensor and DME relay - all at different times of course.
If you've able to rule-out TPS and DME (which can be easily diagnosed with a jumper), you might look at reference sensor(s) next. When my ref. sensors acted up, it would run for a while then cut out without warning, sometimes after a minute, sometimes after about a half hour.
Of course, I'd love to be wrong about this since the sensors are not an inexpensive item.
Good Luck,
-Robert
11-06-2013, 06:22 PM
#17
Surging with a partially open throttle would have me looking at the AFM. Theory is the AFM is sending erratic air readings to the DME, so DME is sending erratic fuel commands to the injectors.
11-06-2013, 06:39 PM
#18
Proprietoristicly Refined
Rennlist Member
Rennlist Member
Here you go http://www.arnnworx.com/catalog/inde...roducts_id=191
That one will make a perfect seal on the factory fuel rail without needing sealing tape or anything like that. I tried making an adapter form a spare fuel rail cap for the HF the one, following the procedure on clark's garage, but it leaked all over the place.
That said, I am at a loss to make any sense of the reading on my Arnnworx one. As you can see he used a 40 bar gauge for measuring 2-3 bar pressure
That one will make a perfect seal on the factory fuel rail without needing sealing tape or anything like that. I tried making an adapter form a spare fuel rail cap for the HF the one, following the procedure on clark's garage, but it leaked all over the place.
That said, I am at a loss to make any sense of the reading on my Arnnworx one. As you can see he used a 40 bar gauge for measuring 2-3 bar pressure
Everybody should buy one.
I have a complete fuel pressure kit in a blow mold box that I get tired of hauling out.
A solution to the fuel leaking on the Clarks DIY fuel pressure guage is to use a beveled washer that fits inside the threads of the fuel rail cap ---bevel facing the rail. The fuel rail cap threads will seal nicely around the washer. Do not overtighten. See picture.
The best beveled washer to use would be gas/oil/grease resistant but a standard water faucet beveled washer works for a couple of times.
Replace the OEM fuel rail cap and torque to 19ft lbs when finished.
J_AZ
11-06-2013, 07:27 PM
#19
You can hose clamp any old fuel pressure gauge to the threads port on the rail if you are sure it doesn't leak and you don't crush the threads. Keep a fire extinguisher near by when opening the fuel system.
Or get a Bosch CIS compatible gauge.
will bolt right on.
Or Star Hoffman TU-447
Or the one on Pelican
Or get a Bosch CIS compatible gauge.
will bolt right on.
Or Star Hoffman TU-447
Or the one on Pelican
11-06-2013, 11:29 PM
#20
Three Wheelin'
Cool tip on the bevelled washer. Actually I didn't know this before but Arnnworx actually sells the special fitting on it's own. For anyone who doesn't have stuff like npt taps and fittings lying around, this is probably the cheapest option to get a perfect seal.
11-07-2013, 08:33 AM
#21
Proprietoristicly Refined
Rennlist Member
Rennlist Member
Cross Referenced-Bookmarked.
Excellent information on both threads.
https://rennlist.com/forums/924-931-...e-adapter.html
J_AZ
Excellent information on both threads.
https://rennlist.com/forums/924-931-...e-adapter.html
J_AZ
11-07-2013, 11:24 AM
#22
Burning Brakes
Thread Starter
Why is your throttle adjusted that way? Seems almost guaranted to cause a bouncy idle. What is your idle rpm?
Surging with a partially open throttle would have me looking at the AFM. Theory is the AFM is sending erratic air readings to the DME, so DME is sending erratic fuel commands to the injectors.
Surging with a partially open throttle would have me looking at the AFM. Theory is the AFM is sending erratic air readings to the DME, so DME is sending erratic fuel commands to the injectors.
11-07-2013, 09:34 PM
#23
Any chance you can borrow a known-good AFM?
11-10-2013, 04:48 PM
#24
Burning Brakes
Thread Starter
Ok. So 1) your rpms were flopping when transitioning to idle and 2) your rpms were surging when warm and throttle open. Disabling the idle switch on the TPS fixed the first one. Got it. I'm tempted to think they are related, but I have no good theory to directly connect them.
Any chance you can borrow a known-good AFM?
Any chance you can borrow a known-good AFM?
11-10-2013, 06:52 PM
#25
Which sensor will you be scoping?
Also, my S had severe hesitation sometimes only after it warmed up (and when air temp was cold). All throttle positions. Chased that one for a long time and it ended with AFM. Not the same symptoms as you (or car for at matter), but don't underestimate how confused the DME gets when the AFM lies to it! Mine was presumably underreporting air when that happened. Yours may be over reporting. Just a thought.
Also, my S had severe hesitation sometimes only after it warmed up (and when air temp was cold). All throttle positions. Chased that one for a long time and it ended with AFM. Not the same symptoms as you (or car for at matter), but don't underestimate how confused the DME gets when the AFM lies to it! Mine was presumably underreporting air when that happened. Yours may be over reporting. Just a thought.
11-11-2013, 09:50 AM
#26
Burning Brakes
Thread Starter
Which sensor will you be scoping?
Also, my S had severe hesitation sometimes only after it warmed up (and when air temp was cold). All throttle positions. Chased that one for a long time and it ended with AFM. Not the same symptoms as you (or car for at matter), but don't underestimate how confused the DME gets when the AFM lies to it! Mine was presumably underreporting air when that happened. Yours may be over reporting. Just a thought.
Also, my S had severe hesitation sometimes only after it warmed up (and when air temp was cold). All throttle positions. Chased that one for a long time and it ended with AFM. Not the same symptoms as you (or car for at matter), but don't underestimate how confused the DME gets when the AFM lies to it! Mine was presumably underreporting air when that happened. Yours may be over reporting. Just a thought.
11-11-2013, 02:11 PM
#27
Burning Brakes
Thread Starter
Just went to check out my DME relay to rule that out as the culprit and I can't find the damn thing. PO must have moved it (the connector and relay are both nowhere to be found). Looks like tonight I will be laying upside down searching the bird's nest that is German wiring.
11-12-2013, 04:52 PM
#28
Burning Brakes
Thread Starter
Found the DME relay behind all the other relays and above the mess of wires coming out of the panel. The relay looks to be very new, it probably got pushed out of the panel when the PO was trying to put in the new one. Onward to some AFM adjustment and vacuum troubleshooting.
11-15-2013, 12:20 PM
#29
Burning Brakes
Thread Starter
Vacuum testing revealed major leaks at the dipstick tube and the throttle body, plus a few minor leaks at hose connections. My throttle body reseal kit is now on its way. Does anyone know the size of the dipstick tube o-ring? Shipping is several times the cost of the o-ring, so I'm hoping to just source it locally.
