Broken AFM...expensive part

[Funky-P]

Today we went back over and tested all of the connections listed in the engine fuel section of the fsm. While I don't it still seems like the afm is not showing the right resistances I don't think it is preventing the car from starting as all the pins to the ECU (6&8,7&8,8&9) all show continuity as well as those to the fuel pump contact points (10&20). All the circuits checked out for continuity for the Fuel pump relay, the air regulator and fuel pump, the ground circuit and the throttle valve switch.

The problem appears to be the water temperature sensor whose circuit does not have continuity. I guess we will try to replace that and hope it is the sensor itself rather than a wiring issue. The troubling thing is that after further investigation it still appears the negative terminal of the battery goes solely to the body to ground without connecting to the harness at all. There has been some rewiring of the harness and connections in various places, likely having to do with the alternate ignition wired in.

Edited October 25, 2010 by Funky-P

[conedodger]

The Water Temperature sensor or Cylinder head temperature sensor as I said before richens the mixture when it senses the head is hot. Since it is a resistance signal, full resistance means the head is hot and the ECU is responding accordingly. Probably a bad connection or a brake in the wire.

[Zed Head]

Conedodger, this car uses the water temp sensor with the attached temperature vs resistance curve. I'm not sure what the CHTS sensor uses. But no continuity or high resistance would be "very cold" to the 77 ECU.

Funky-P, from your answer, I'm guessing that you're looking at the wiring diagram also? Measuring 10 to 20 instead of 36 to 39. Still no numbers though, and no reports of fuel pump working (you can test it separately from the relays, just run 12 volts to it and listen) or fuel flowing. Don't forget that 0, 100, 180 and 1,000 ohm will all show "continuity." You really need the numbers.

Read this thread from the past. Lots of good measurements and a positive outcome - http://www.classiczcars.com/forums/showthread.php?t=37299 .

The major difference to your situation is that her car was running at the time. Still not clear why you're focused on the AFM. Confirm fuel flow, fuel pressure and spark first.

[Funky-P]

I'm checking the continuity based on the continuity check setting on the multimeter, so it doesn't give number values. What I figured today was that the afm may be bad, but not likely to be the main problem. I did not recheck the connectors directly on the afm, but the various connectors on the harness to the ECU. Yes I've been referencing the wiring diagram as well. It smells very strongly of fuel in the components. Could not check the spark yet, I needed to get a tool first, so its next up. I'm not sure what the process is for checking the actual fuel pressure is, but I will check as to whether the pump itself works.

I've been going over the issues in the order specified in the FSM, hence checking the continuity circuits before the pump itself, which was my original thought to do.

I probably wont have time to do any more checks over the next few days.

[MikeO]

Hey all,

Perry grabbed the tools we needed to check the spark plugs but is going to be busy this week with work on top of school. I am going to try and get some other things checked out while he is doing his thing.

if someone could inform me on the procedure to check fuel pressure and what is needed to do that? I've done a search on the forum as well as google and couldn't find anything.

Thanks,

Mike

[conedodger]

Hey all,

Perry grabbed the tools we needed to check the spark plugs but is going to be busy this week with work on top of school. I am going to try and get some other things checked out while he is doing his thing.

if someone could inform me on the procedure to check fuel pressure and what is needed to do that? I've done a search on the forum as well as google and couldn't find anything.

Thanks,

Mike

You have to break the fuel line at some point and put a gauge in-line. I think if memory serves the FSM also calls for a check of the quantity pumped in a minute as well...

[sblake01]

The gauge goes inline between the outlet of the fuel filter and the fuel rail. If you have the 1977 FSM the test procedure is on page EF-58. I tried to scan it but since my 77 manual is a copy of a copy of a copy (etc.), it doesn't come out too clear.

[Funky-P]

Okay so we finally had some time to get some more work done today.

We found that the spark plugs were no good so we replaced and now we are getting spark.

We replaced the water temperature sensor and the continuity check for that circuit is now good.

We did the sound check for the fuel pump, didn't get any sound. We removed the fuel pump and checked it by just running it directly off the battery and it worked. So it seems the circuit to the fuel pump is disrupted, tomorrow we are going to try to trace the circuit and hopefully find out what the problem is.

I think the cold start valve may be no good as well, when I ran it off the battery before disconnecting the fuel pump I didn't notice any sound or anything. I'll look into that further as well I guess.

I think we're getting closer to getting this thing started, or at least I hope so.

[Funky-P]

The continuity for to the fuel pump checked out, so we went to check the ECU. Using the lamp to injector harness method it appears that the ECU is not functioning properly as we got no pulse. The car came with two ECU's, both of which gave the same result. Is there any other situation that would prevent the injectors from getting pulsed? It seems a little unlikely that both ECU's are bad, but I wouldn't be all that surprised.

[Zed Head]

What is the "lamp to injector harness method". A test light in series with an injector? Watching for flashes?

I think the injectors should have twelve volts to them at all times. Testing is described on page EF-23. They fire when current flows and activates the solenoid. Current flows when the ECU grounds the circuit. That is my current understanding of how the EFI works. I could be wrong.

[sblake01]

Not true. The dropping resistors bring the voltage at the injector down to roughly 9 volts from what I have observed. Top of page EF-15 mentions this though it doesn't state the actual voltage.

[cozye]

The ECU doesn't control when the fuel pump comes on.

There is a 5 blade relay in the relay bracket. When you turn ignition on, it should turn the fuel pump on. Look for a white/black wire with 12v going to that relay. Test the relay.

The ECU gets power from the 6 blade FI relay right next to it. So you might as well test that relay while you are there. Test procedure for the relays is in the FSM under the EF section.