1.8 L injector resistor block
 

Does anyone know a recommended way to test it?

Ohm meter? It's just a resistor so the ohm scale on a DMM...

There are four resistors, and they are tied together at one end, and wired separately at the other (injector) end. A fifth wire (that travels to terminal 88b on the double relay, then on to pin #10 at the ECU) travels from the 5-pin male/female connector into the middle of the four resistors. I'm getting weird, inconsistent readings with my ohm meter and I'm trying to determine if the block might be shorted.

I can't find any specs for the resistors, or a procedure for test points, or instructions to disassemble the block, if possible, to measure the resistors individually.

Measure the resistance from the common connector to each of the other 4 terminals to test each of the 4 resistors. Each resistor should measure about 6 ohms.

Pete
75 914 1.8L

Thank you for the info! I get 7.4, 7.4, 7.4 and 7.4. For the 5th wire (resistor block to pin 10, ECU, through the double relay) I don't get anything but continuity; what is that wire supposed to do?

I don't have an L-jet car any more, so can you describe exactly what you're testing with that 5th wire? Where are each of the probes when you check it?

If the probes are on both ends of a wire, and not passing through any sort of component, then continuity is what you expect and want to see...

--DD

Dave, the meter probes are on the end of the wire inside the 5-place connector, and the other probe is on the downstream side of the resistors, where it is captured in the metal piece that connects the resistors. This explains the continuity, but I've got a call in to the guru who checked my AFM & ECU, I hope to hear from him today and learn what that wire does.

I just re-read my previous post and realized my description wasn't very clear. Sounds like you figured it out though.

The wire that goes down through the middle of the block of resistors just connects the opposite end of all the resistors together and brings that connection out to the connector. If you measure from the common resistor connection to the terminal, it should show continuity or very low ohms. Measuring from the common terminal on the connector to each of the other 4 terminals should measure the resistance of each resistor. Your measurement of 7.4 ohms for each sounds fine to me.

Pete
75 914 1.8L

Well, I just rec'd my known good, used, resistor block, and it tests almost identical to the old one in the car. So much for that being my running problem. Maybe I'll pull the harness and check every contact. Hmmmmm...

One more discussion point; compression. Does anyone have a spec for how much an L-jet engine should have? When I did my valve adjustment I found valve covers almost filled with condensation rust. After the covers were on and fresh oil added, I did a compression test. Range was 108 (low) to 112 (high). My fear, now, is that the piston rings are seized in their ring grooves, and low compression is interfering with combustion chamber efficiency/off-idle running. Thoughts?

110 PSI is on the low side. By the time it gets to 100 PSI, the top end is badly worn.

However, lots of things can affect a compression pressure reading. Throttle open/closed, battery charge state, engine warm/cold, altitude, etc.

--DD

Dave; Test done on cold engine, 75F ambient, throttle open, battery new & strong, Bakersfield. I would try a leak down test, but many years ago, when the shop did one, I remember that it was really hard to find OT and keep the engine from spinning with the air pressure in the tool. Maybe I should give this a try anyway.

I put PB Blaster into the cylinders this morning, then cranked the engine, by hand, through a few revolutions. Hopefully the liquid will reach the rings.

This is really puzzling because the exterior/top of the engine was incredibly filthy (the story is that the car hadn't run in 8+ years), but looking through the spark plug wire holes in the shrouds the heads are nice and clean. After I started and ran the engine a few times I did a valve adjustment, the covers were full of condensation rust, but the valve clearances were surprisingly close. Also, the engine doesn't leak. Almost like the PO bought an exchange engine from a re-builder, stuck it in, tried to get it running but couldn't (because of any number of issues on the car that I've already fixed), and just said heck with it.

I'll do another compression test tomorrow and post the numbers if there is a change.

If it's cold, those are probably reasonable numbers for a well-loved engine. Bakersfield isn't Denver, so the altitude isn't a factor.

Might as well try to get it running. :)

For the leak-down, find a way to keep the engine from turning. A flywheel lock would work. Putting it in gear with the brakes on should work, too, but with more slop.

--DD

Thanks, Dave! We did figure out how to keep the darn engine from spinning, but I'll be darned if I can remember how (I didn't do much 914 work myself at Red Line - 911 transmissions, fuel injection and carbs kept me plenty busy)! I'm pretty sure that we blocked the flywheel, I'll take a look at my car later today.