Will start but not run... :<

[chitwnvw]

Anyone know what this is:
Between the plenum and the #3 plug?

Help us out.
Is that a vacuum hose? Does it attach to a nipple?
Colin

That is a vacuum hose, attached to a nipple, running forward through the tin. There is another nipple capped with a rubber cap next to it.

[chitwnvw]

Alright, made some progress. Was running through the FI troubleshooting procedure and discovered that the two wires to 88B on the double relay were pulled a bit out of the white connector, it was pretty subtle, the wires and spade were in the connector, just out a bit further than the other wires. Got it seated and now it will start, but it doesn't want to idle, have backfiring, and I have to nurse it along with my foot on the accelerator pedal. It also goes from low RPM to really high RPMs with very little movement of the accelerator pedal.

Any ideas?

[Amskeptic]

Alright, made some progress. Was running through the FI troubleshooting procedure and discovered that the two wires to 88B on the double relay were pulled a bit out of the white connector, it was pretty subtle, the wires and spade were in the connector, just out a bit further than the other wires. Got it seated and now it will start, but it doesn't want to idle, have backfiring, and I have to nurse it along with my foot on the accelerator pedal. It also goes from low RPM to really high RPMs with very little movement of the accelerator pedal.

Any ideas?

Once the engine reaches a certain rpm, it takes off because it is exceedingly happy. That means down at idle, it is exceedingly unhappy. Your job is to find what is making it unhappy at low rpm:
vacuum leaks (don't forget about valve cover gasket droops)
lousy breaker point gap/dwell/timing
ad infinitum
Colin

[chitwnvw]

Once the engine reaches a certain rpm, it takes off because it is exceedingly happy. That means down at idle, it is exceedingly unhappy. Your job is to find what is making it unhappy at low rpm:
vacuum leaks (don't forget about valve cover gasket droops)
lousy breaker point gap/dwell/timing
ad infinitum
Colin

I've been over and over the vacuum system, nothing seems so out of sorts to give me this kind of behavior.

I unplugged the AFM plug, though, and then it will idle at about 3500-4000 rpm. So something is telling the AFM what?, to make it run so lousy?

[Amskeptic]

Once the engine reaches a certain rpm, it takes off because it is exceedingly happy. That means down at idle, it is exceedingly unhappy. Your job is to find what is making it unhappy at low rpm:
vacuum leaks (don't forget about valve cover gasket droops)
lousy breaker point gap/dwell/timing
ad infinitum
Colin

I've been over and over the vacuum system, nothing seems so out of sorts to give me this kind of behavior.

I unplugged the AFM plug, though, and then it will idle at about 3500-4000 rpm. So something is telling the AFM what?, to make it run so lousy?

I will be in Chicago August 22/24. I can't guess further at the keyboard.

[chitwnvw]

So Colin came out and we troubleshot the FI system. Everything checked out. Maybe Colin can remember better than I, but I seem to remember that it liked running without any fuel. Now the '75 has a one year special 6 pin afm, and I didn't have another of those, but I did have a couple of the later 7 pin afms. So I swapped out the '75 pin afm and wiring harness for an older afm.

Now here's what I've got. Spark. The fuel pump starts when the wiper on the afm is moved to the left. Getting a squirt out of the cold start valve. But I am not getting fuel squirting from the fuel injectors. So it turns over but doesn't run.

Can someone help me with a refresh on how the fuel injectors are fired? I had the bus towed out to my Dad's place and am heading out there tomorrow to try and get it running. He's getting a little tired of not being able to get in and out of his garage.

Thanks. Todd.

[dtrumbo]

First of all, welcome the hell back! Where ya been, huh??

Then, The injectors are powered with 12 volts from the double relay that passes through the 'resistor pack' (I think it has a more official name, but that's what I call it). Said pack has four resistors in a little silver can and is mounted directly above the double relay. Each of the four resistors then allows current to flow to each of the four injectors. The ECU provides the ground (at the proper duration) to fire the injectors.

Long story short, check the while nylon plug at the resistor pack and the double relay connections as well.

And again, welcome back!

[ruckman101]

I will second that sentiment, welcome back.


neal

[Amskeptic]

Now here's what I've got. Spark. The fuel pump starts when the wiper on the afm is moved to the left. Getting a squirt out of the cold start valve. But I am not getting fuel squirting from the fuel injectors. So it turns over but doesn't run.

Does it fire while cranking then die?
Does it not fire at all?
Colin

[chitwnvw]

It's not firing at all.

I am getting power off of the coil but not out of 88b at the double relay. Can I confirm I am doing this test correctly? I pull the plugs off of the double relay, and with the key in the on position I put a test light in line between 88b and ground. Doing this it isn't lighting up.

[Amskeptic]

It's not firing at all.

I am getting power off of the coil but not out of 88b at the double relay. Can I confirm I am doing this test correctly? I pull the plugs off of the double relay, and with the key in the on position I put a test light in line between 88b and ground. Doing this it isn't lighting up.

Once you unplug the connectors from the double relay, the double relay cannot send electricity to where it has to go.

The double relay itself sends 12 volts to 88b, so it has to be plugged in.

If you are not getting any firing, you MUST confirm ignition system is good. Point gap? Spark from coil wire to center of distributor cap? White wire on coil (-) ?

Remember that there is also a black wire from coil (+) to double relay, this is critical. It branches off the upstream side of the reverse light fuse on left side of engine compartment.
Colin

[chitwnvw]

Thanks, Colin. I'll study the Bentley and take your advice. Hopefully, 3rd time will be the charm.

[Jivermo]

So, what happened here? This is interesting.

[Amskeptic]

So, what happened here? This is interesting.

Notice the 13 month gap above. Might want to take off your shoes and have a cup of tea.
Colin