injection wiring harness questoins

Michael Stone · 03-26-2003, 08:41 PM

I am rebuilding a 1975 914 that was originally a 1.8 liter. However, what I started with was the body, no engine or trans. The injection control unit and the air intake valve were with the car. My question is, I obtained a 1974 1.8 liter with the injection wiring harness but it will not plug into the air valve. Can I change the harness to a 1975, and use my existing control unit and air valve or do I need to change everything to 1974 vintage?

jamcleod · jamcleod's Garage

want to help out a fellow 1.8'er... i have a 74 1.8 (all whopping 76 hp of it.... not complaining)

air intake valve... are you referring to the air flow meter? the plastic box on the top of the drivers side of the engine is the air filter housing and the AFM has a "vane" that deflects in reaction to amount of air flowing through and is just "downwind" of the air filter. if i recall, my 74 has 3 terminals and i think 75's have 4. ("not gospel"). can't help out with the difference, sorry, but i don't see why if you have all, say, 74 FI parts, it wouldn't work on a 75 long block.

jamcleod · jamcleod's Garage

or vice-versa

chibone_914 · 03-27-2003, 11:35 AM

Hi Michael,
Try getting a hold of Jeff Bowlsby, He seems to do great work with harnesses according to Steve here.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

URL for Jeff's page--
http://members.rennlist.com/914_wiring_harnesses

He refurbs D-jet harnesses, not L-jet so far. But he has lots of good info on the year-to-year differences, wiring specifics, and so on.

I think the 75 has the five-pin AFM connector and the 74 only uses four of the five pins in its connector. The extra pin in the 75 is for the intake air temp sensor. I think you can just plug in the connector and it should work. ...I think....

You might mean the Auxiliary Air Regulator, or possibly the Thermo-Time Switch? Or or the other of those went from a single-wire plug to a two-wire plug in 75. I believe that the added wire is a separate ground wire, while the earlier part(s?) grounded through their cases.

--DD

Kenny Powell · 03-30-2003, 04:00 PM

74' has 111111 pins
75' has 1111111 pins harness to air flow meter

ejm914 · 03-30-2003, 06:45 PM

Michael - As I understand your question:

You have the ECU and AFM that came with your '75 and the harness that came with a '74 motor?

In '75 a new temp sensor was added to the airflow meter. To use the '74 harness you would need to change the connector at the AFM and run a wire from the additional terminal to pin 27 at the ECU. Everything else should be the same.

L-jet was the first to use a thermo-time switch for the cold start valve. With D-jet, if the temperature was low enough the single wire switch would let the CSV spray fuel as long as the starter was engaged. The engine would flood if it didn't start quickly. The two wire switch used on L-jet limits how long the CSV sprays. One wire provides a temperature dependent ground for the CSV, the other wire heats the sensor using the starter terminal 50 for power. This limits CSV operation to around 7 seconds. Both switches are grounded through housing/mounting bracket.

bowlsby · 04-01-2003, 08:12 PM

Quote:

L-jet was the first to use a thermo-time switch for the cold start valve.

Actually the 75-76 D-Jet cars also have a 2 pole TTS, as well as the L-Jet cars. This extra circuit is the primary reason that the 75-76 2.0 wiring harnesses cannot be used on any of the other 914 D-Jet cars without modification.

I have recently come to find out that there are actually at least 3 different L-Jet set-ups for the 74-75 1.8 914s. Previously I thought there were only 2. None of them are interchangeable becasue of the particular FI system requirements, and my website noted above (thanks DD!) will be revised soon to reflect the new information.

There are two 74 1.8L L-Jet setups (both known by the 6-pole Air Flow Meter (AFM), here is how to tell them apart:

74A: 2 wires in the TPS plug, no 3-wire branch near the ECU for the altitude optional compensator

74B: 3 wires in the TPS plug, and a 3 wire branch near the ECU for the optional altitude compensator (likely just bare wires not connected to anything)

75: 3 wires in teh TPS plug, and a 7 pole AFM...yep with the added wire 27 going back to the ECU.