Runs only with air flow meter disconnected Options

[Jerlle]

I posted this question over on Pelican Parts and it has only gotten a bunch of views so far so I thought I'd post it here too. Here is the link to the post on Pelican Parts for reference.

I recently had a problem with the number 1 and 2 cylinders not firing. It occurred during a drive but I was able to limp home on 2 cylinders.

I checked the compression, which was good. I then checked if there was any fuel going through the injectors by having a friend crank the car with the injectors out of the manifold and pointed into a jar. Nothing came out. I had an extra complete injection manifold with wire harness so I decided I'd switch the harnesses (the one in the car was very brittle and cracked.

During the removal I broke the connector going to the air temp sender just under the plenum. So I ended up removing the manifolds and plenum to replace the sending unit. While everything was out I cleaned it up and switched the throttle body that had the single vacuum port with a dual vacuum port I had from the extra injection unit.

After installing everything back in the car it fired right up but then raced the engine up to about 3500 to 4000 RPM. I discovered I had neglected to hook up the air flow meter and did so. After connecting the electrical connector to the air flow meter and doing another check that everything had been installed and connected I started the car again. This time it would not catch and idle. It would fire just long enough to dab the throttle and keep it running by modulating the throttle. While holding the throttle to where it seemed it would stay steady at approximately 1500 RPM it would slowly move there as I increased throttle but tended to take off revving very quickly up to 3000 RPM. In other words the throttle seemed very touchy at that point.

The one thing that I am a little uncertain of is if the wires going to 86a, 86c, and 85 on the left side of the relay box (fuel pump side) are connected to the correct terminals as one or two of the wires had fallen out or broken during the operation. I installed them how I remembered they went and tired to double check with my book but the purpose of the wires (not the terminals, I understand that 85 is ground, 86c is the coil) are readily apparent to me. Since the car seemed to start (sort of) I didn't believe them to be a problem. The fuel pump is running fine as I can hear it and the car doesn't run out of fuel while keeping it running with the throttle.

I attempted to adjust timing and idle air flow to see if that would help but nothing seemed to do the trick. So there is where I am. Sorry for the long explanation but I hoped it would narrow down the possibilities of the current problem.

[Cap'n Krusty]

Before we even begin to discuss this, you might as well stop the guess work on our behalf and tell us what engine and what FI system you have. Good questions have a better chance of getting helpful answers ......................

The Cap'n

[Jerlle]

Before we even begin to discuss this, you might as well stop the guess work on our behalf and tell us what engine and what FI system you have. Good questions have a better chance of getting helpful answers ......................

The Cap'n

It is a 1.8 with L-jet. Sorry. Does D-jet even have an air flow meter?

[Cap'n Krusty]

Before we even begin to discuss this, you might as well stop the guess work on our behalf and tell us what engine and what FI system you have. Good questions have a better chance of getting helpful answers ......................

The Cap'n

It is a 1.8 with L-jet. Sorry. Does D-jet even have an air flow meter?

Doesn't matter, we need to know. Could be a 912E, or even a T1 or T2, for that matter. Even a 280Z, an Alfa Romeo, or a 928. All the same, all different. NOW we have a baseline. In a stock L-jet system, the fuel pump doesn't run when the AFM isn't connected. You have one problem there. There is no FI related "air temperature sensor" anywhere other than inside the AFM, so we have a questionable repair there. In a D-jet system, intake air leaks, up to a point, make the engine idle faster. In an L-jet system, the engine won't start at all with even seemingly minor air leaks. There's a problem there. In swapping the components, did you recognize the fact that '74 and '75 L-jet systems are somewhat different? '74s use dual vacuum controls, 'most '75s use single vacuum control. There's likely to be a difference in the throttle switches, and the AFMs use different wiring. Can't just mix 'n match. IIRC, even the dual relays are different. If 2 injectors aren't firing, the FIRST thing I would look at is the resistor pack, then all the system grounds. If you didn't replace the intake air hoses at the runners, do so, as well as the injector seals. Check the throttle cable. If you'd like a copy of the factory L-jet troubleshooting manual, PM me with an e-mail address that will accept large PDF files. Be sure it works, 'cause I'll only send it ONCE. Once you've undone all the damage and it runs, set the timing using the L-jet timing procedure, which is completely different from the D-jet procedure.

The Cap'n

[Jerlle]

Before we even begin to discuss this, you might as well stop the guess work on our behalf and tell us what engine and what FI system you have. Good questions have a better chance of getting helpful answers ......................

The Cap'n

It is a 1.8 with L-jet. Sorry. Does D-jet even have an air flow meter?

Doesn't matter, we need to know. Could be a 912E, or even a T1 or T2, for that matter. Even a 280Z, an Alfa Romeo, or a 928. All the same, all different. NOW we have a baseline. In a stock L-jet system, the fuel pump doesn't run when the AFM isn't connected. You have one problem there. There is no FI related "air temperature sensor" anywhere other than inside the AFM, so we have a questionable repair there. In a D-jet system, intake air leaks, up to a point, make the engine idle faster. In an L-jet system, the engine won't start at all with even seemingly minor air leaks. There's a problem there. In swapping the components, did you recognize the fact that '74 and '75 L-jet systems are somewhat different? '74s use dual vacuum controls, 'most '75s use single vacuum control. There's likely to be a difference in the throttle switches, and the AFMs use different wiring. Can't just mix 'n match. IIRC, even the dual relays are different. If 2 injectors aren't firing, the FIRST thing I would look at is the resistor pack, then all the system grounds. If you didn't replace the intake air hoses at the runners, do so, as well as the injector seals. Check the throttle cable. If you'd like a copy of the factory L-jet troubleshooting manual, PM me with an e-mail address that will accept large PDF files. Be sure it works, 'cause I'll only send it ONCE. Once you've undone all the damage and it runs, set the timing using the L-jet timing procedure, which is completely different from the D-jet procedure.

The Cap'n

It appears that a previous owner must have swapped in some or all 75 parts as this car is supposed to be a 74 but had the single vac control. As I was thinking about this last night after I ran out of daylight. I decided today I'd switch back to the single vac control throttle body and see if I created this problem from something as simple as that. I wasn't planning on taking off the runners so I didn't have new hoses. I will source some of those this week to eliminate any vacuum problems. I did replace the injector seals (both sizes, apparently a previous owner never installed the smaller seemingly more important ones). Throttle cable is free and unbound and returns to closed position on its own.

During some reading yesterday I saw something that mentioned the resistors for the injectors (I believe it was the electrical schematic in a Haynes manual). I am not familiar with their location so if the L-jet trouble shooting guide identifies this that would be great. I'll send you a PM shortly.

I am familiar with what I believe to be the L-jet timing procedure which is done at idle with the vacuum control lines removed from the distributor.

I'll let you know what happens with the single vac control TB re-installed.

Edit:

As far as the "air temp sensor". It was the small device that connects to the FI harness under the plenum (not the aux air flow). Nothing goes in or out of it other than the connector so I assumed it was a temp sensor. Regardless of what it is it was replaced with a used component from an extra 1.8 engine and connected to the same spot on the FI harness.