Troubleshooting help 1.7 FI, Updated: I almost have defeated the D Jet Demons! Options

[Robarabian]

Thank you to the collective here, I learned alot. As of yesterday, the car starts, idles higher when cold, settles after the AAR opens. The throttle is responsive. The MPS works, the throttle position switch was re-set and the timing is spot on at 27 degrees and the 123 ignition is working well and playing along with its new friends. . No pops, no backfires.

I took a smart suggestion and did swap out the 71 non adjustable brain box for a 73 1.7 brain box with the knob. That particular setup (thank you @MM1 ) had a very intact wiring harness so I swapped mine for it. Having the knob certainly helps it run smoother.

The last item to deal with is the air intake temperature sensor. It is unplugged right now and runs great. When I plug it in, the idle suffers and it hunts and hunts. So I have ordered a replacement and hope that will solve it. Everything else has been checked and / or replaced / upgraded so I'll cross my fingers there.

The best troubleshooting process was to disconnect everything except the MPS and plug the holes to determine if there was a vacuum leak somewhere, and then plug things in 1 at a time. As I did that, I located the likely faulty sensor.


Again, thank you to everyone who chimed in, your collective ideas kept me from ripping the FI off of it. I know how much better the car will be in stock FI form--in both MPG and value. This literally gets me to now assemble the interior and install the front windshield. Hopefully Hi-Hi Silver will be at a local 914 World Event soon.

Robert
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I am trying to button up what I call "Hi Ho Silver" a 71 I bought during Covid.

Motor is rebuilt by me and cam break in went well, 8-10 months ago. How time flies. I had an oil leak, so I pulled the motor today and located it, resealed it and put the drivetrain back in.

Car now has a 1,2,3 ignition for FI cars. It has only one nipple for vacuum, so the hose from the top of the throttle body is connected to the nipple on the distributor, the bottom vacuum port on the throttle body is capped off. The timing has not been further adjusted, as it wont run long enough without throttle to do that. (I only have 2 hands).

Turn the key, fuel pump kicks on, and the car will start pretty easily with the key turn. It will light, then die within a few seconds. Fuel pressure is at 30 PSI based on the inline gauge.

I can start it and with throttle, keep it running. My best description is that with 0-1/4 throttle won't keep it running, I have to sort of put my foot in it. When it warmed up a bit, it sort of idled, but lobed up and down, to the point it wanted to stall but would catch itself at the last second, and lobe up again. I think this is my best symptom....

The MPS is stock, and holds vacuum and also checked out on the meter.

I've looked at every vacuum line and things are plugged. The car is not driving as of yet in the build process, I am trying to stabilize it so I can work toward a drive down the street.


Any FI info would be helpful. I really want to keep it as stock as possible. I will check all the valves again tomorrow and make sure they are in spec.

Thoughts on where to troubleshoot?

Thank you in advance.

[914_teener]

Ok but the air bleed screw should be your last adjustment.


Here is a copy and paste from Brad Anders site for the Air Temp Sensor and the test procedure:

Function: Senses intake air temperature and sends signal to the ECU to provide mixture compensation.
Normal Value(s): 300 ohms @ 68 deg. F, about 100 ohms @ 122 deg. F.
Failure Modes
Open: Makes the mixture somewhat richer. Check with an ohmmeter.
Shorted: Makes the mixture somewhat leaner. Check with an ohmmeter.
Notes: The output of this sensor is used by the ECU to adjust the mixture for the intake air temperature. This is a secondary adjustment and has a small effect on the mixture. The sensor corrects for the decrease in air density with increasing temperature by leaning out the mixture. Disconnecting this sensor has the effect of richening the mixture, a common mechanic's trick.
More: This sensor and the cylinder head temperature sensor are negative-temperature-coefficient (NTC) thermistors. Here's a URL on thermistors and how they work:
http://www.rtie.com/ntc/ntcappln.htm

Here's a URL that describes the manufacturing process:

http://www.ussensor.com/manufacturing.html

Below is a URL to a reference that has two charts showing the resistance vs. temperature relationship for the intake air sensor and the engine temperature sensors used in D-Jetronic. The engine sensor data looks OK (about 2.5K at 68 deg. F), but could be from any sensor. Bosch used the same air temperature sensor on all D-Jetronic cars, regardless of model, so the data should be accurate for the 914's sensor:

http://www.icbm.org/erkson/ttt/engine/fuel...tion/d-jet.html

The charts are about half way down the page.



Read the page on idle stability. I'd use an ECU with the adjustment knob. It's also possible that you have a ground problem...which you can test for resistance. Make sure your ground strap is new or you could be chasing your tail...like you are. But it looks like it's not the timing.

My quess in you still may have a vaccum leak, leaky or bad PVC valve.

I'd test every single component but since the engine was out....a bad ground somewhere.

Memorize or reference Brad Anders site. All the answers are there.