1978 930 Fuel pumps on w ign on - and injectors spraying

[jsveb]

Well, it's spring and I decided to bring the 930 out of hibernation.

When I parked it last year, I noticed the fuel pumps started to come on as I turned on the ignition. However, it ran fine, so I decided to tackle it as a winter project... Here I am, it is spring, and I won't bring the car back out, before I have sorted this out.
Furthermore, I am pretty certain, I can also hear the injectors spraying - and smell it.
Here is where I am at. The injectors lines are now soaking in Gibbs.


I have removed IC, airfilter etc. The airflow plate sits flush and the plug that triggers the pumps is plugged in.
I also tried to unplug the pump relays to see if that was the culprit. It wasn't.

Question: Any suggestion to what is causing this?

I am also planning to check injector flow, as I haven't done that since posting about it during my time living in Alabama. The Bottles you see on the floor are special injector balancing equipment purchased in Walmart, enterprise AL.

[908/930]

If you unplug the switch on the airflow plate do the pumps still turn on? Switch or relay stuck.

[jsveb]

Yes,the pumps still run with the switch unplugged.

I have tried switching the front pump relays, no diff.

Thanks for chiming in.

[908/930]

There is another relay to check, airflow sensor relay (also charging pressure relay) mounted on engine bay relay panel behind yellow relay part 911.615.109.01. that is the one that turns on the fuel pump relays, the airflow sensor contact energizes it, so probably the issue. That one turns off the pumps if you go into over boost so quite important.

I am reading this from a 1987 wiring diagram so could be slightly different.

[T77911S]

if you remove the connector on the rear of the AFM the pumps WILL run.
yes the switch in the AFM energizes the relay but when it does it turns the pumps OFF.
if you remove the yellow rly the pumps should go off.
you probably have wither a wiring problem between the YEL RLY and AFM or more likely the switch is not making contact or there is no ground

checking injector flow is always good to know.
check for leakage with the sensor plate at rest.
I like to check for flow at a simulated low RPM (like idle but it takes a loooong time).
then at WOT. connect a battery charger up set to 10amps.

a rich idle setting can make the injectors flow with sensor plate closed.
a stuck plunger in the fuel dist can do it too. I don't hear to much about the 930 ones sticking, but it is possible.

remove the YEL RLY.
with a MM connect it between pin 85 and 86, if it lights the AFM is good and the RLY is bad.
if not, connect it between 86 and ground and verify 12v. if you have 12v then the wire/sw/ground is bad at AFM, probably SW not making contact.

for a test light
clip it to 12v and check pin 85 for ground/sw connection
clip it to ground and check 86 for power.

[jsveb]

Thank you both!

Now I have something to go by.

I’ll report back

Cheers

[mark houghton]

Subscribing to this one. I've lived with the same thing and haven't taken the time to trace the problem. I have a relatively new yellow relay, pumps run with or without the air flow switch plugged and injectors flow fuel with ignition on but engine not running. Mixture adjustment is not cranked down to where the air flow metering plate is deflected enough to trip the switch. I figure it's either a ground/wiring issue from the switch itself, or the switch is bad, or an issue with the fuel distributor.

I've just lived with it, the only real issue being that I don't dare leave the ignition on for any length of time before starting the car; fuel injecting will flood the engine in short order if the car isn't running. Makes for a great starting enrichment, though, the cars fires up instantly even after long winter storage.

[T77911S]

the mixture adjustment deflect the sensor plate and turn on the pumps.
but the mixture adjustment WILL fire the injectors.

I want to say mine did the same thing but I know I had my mixture rich due to FD issues.
if your pumps done run with the key on and engine off you would never notice anything,

[908/930]

With mine as I turn on the ignition the pumps turn on for about 1/4 second and shut off again, as far as I know this is how it is supposed to work, probably a delay in how fast a relay can open.

[mark houghton]

Originally Posted by 908/930

With mine as I turn on the ignition the pumps turn on for about 1/4 second and shut off again, as far as I know this is how it is supposed to work, probably a delay in how fast a relay can open.

That's normal. With CIS, pumps running and fuel injecting are two separate things. What we're talking here is the injectors flowing fuel when the pumps are running but the engine is off. They should not flow fuel unless and until the air flow metering arm is deflected enough to open ports in the fuel distributor. At rest, engine not running, that shouldn't happen.

[908/930]

Just thinking that the pumps should not be on to begin with so if they are to fix that problem first. By having the pumps running without engine running is there a chance that it raises the pressure enough to cause the injectors to flow, or leak?

[mark houghton]

Originally Posted by 908/930

Just thinking that the pumps should not be on to begin with so if they are to fix that problem first. By having the pumps running without engine running is there a chance that it raises the pressure enough to cause the injectors to flow, or leak?

Gotcha. Even if the fuel jumps running is a fault somewhere, vs. forced to run by unplugging the AFM switch, there should be no fuel injecting until the engine is running. There are CIS experts here that have intimate knowledge of the fuel distributor and how bad seals etc may allow this to happen. But to your question, no, pumps running with engine off will not allow fuel through the injectors under normal situations.

[timc]

Originally Posted by 908/930

With mine as I turn on the ignition the pumps turn on for about 1/4 second and shut off again, as far as I know this is how it is supposed to work, probably a delay in how fast a relay can open.

normal, relays are energizing. T77911s can be more specific if needed.....

[T77911S]

if the FP runs with engine off and injectors are spraying, that is either mixture setting or leaking injectors,
mixture setting or pressure will NOT turn on the pumps. remember you should have pressure pushing the sensor plate closed. (with everything working as it should).

if the FP runs with engine off it is most likely the switch needs to be "calibrated" (bent). as it is not closing.
it could also be that the resting position is not set correctly.
or its the rly itself, wiring or no ground.

[jsveb]

Well, the world got turned upside down since my initial post, but here I am with a little progress - not done yet following your advice.

Today I tested the air meter contact switch. It appears to work fine.
I checked it by measuring continuity between ground and pin 8 on the main plug in the engine bay.

I also checked the injectors. They are NOT spraying with ign on. However, the FP still runs. Need to pursue this one further.

I tested the injectors. Here is what I got from a 30 sec. run:


CYL 1 and 4 gets a little less fuel (opinions, please).
The last mech that worked on the fuel head was Franz Blam.

Let me know what you think.

[356911930]

jsveb,

The injectors could be adjusted just fine. I'm only guessing, but cylinders #1 and #4 usually run cooler and therefore do not need excess fuel to keep them cool. Cylinders #2 and #5 notoriously run hotter, being in the middle with hot cylinders on each side, and it has been suggested to run them a little richer. Cylinders #3 and #6 are in the far end of the engine away from the fan and probably need a little help cooling by running them somewhat richer too.

I'm sure that others with more experience in this area will chime in.

Rahl

[jsveb]

Hi Raul

Thanks for chiming in.

I am aware of the flow characteristics of the pancake manifold from reading this forum. Apart from not being completely balanced from left to right bank, I am not certain how it should look in reality; Injector flow vs. afr on each cyl.

Cheers

Jesper

[flightlead404]

Originally Posted by 908/930

Just thinking that the pumps should not be on to begin with so if they are to fix that problem first. By having the pumps running without engine running is there a chance that it raises the pressure enough to cause the injectors to flow, or leak?

I believe the pumps are supposed to come on for a brief moment specifically to bring up the system pressure to make starting easier especially when hot.

they should not run however unless the ignition is in CRANK or in RUN and the AFM is deflected.

[Miguel Antonett]

The pumps must not run unless the engine is running, it is very unsafe to have the pumps pumping all the time, just imaging during/after a wreck... You have a "rigged/bypassed" relay there instead of the OEM one that gives the green light to the pumps to pump as soon as the engine start spinning.
The bypasssed relay is good for certain things like prevent "vapor luck", or during some testing and stuff like that but very unsafe for regular driving and worse case the track!!!

[Alan L]

The fuel flow volumes should be measured accurately - rather then visually. A calibrated measure - I use a 100 ml lab measuring cylinder - good to around 0.5ml. Or you can weigh them - using a tared weight.
When you get some numbers of those measurements, post them up. I do not compensate for #s 2&5. I set them all same - as near as I can get. Mine is only used on track, ie mainly WOT.
If you want to spend the time, you should be able to get them to withing 2-3% variation between high/low. Porsche suggest for my SC that within 10% is OK. But if you are going to adjust them, why not get them as equal as possible - it helps the low throttle running a lot. If you can't achieve 2-3% then you have an injector or FD issue.
It seems the injectors are not flowing with static engine now? But as suggested - one thing that will do that is the idle adjust is too rich. It is a fine line. The only way the pumps can run with key On is that they have an earth they should not have. When you crank the engine it sucks air and pulls the airplate off the switch contact in the back of the AFM. That allows an earth contact to run the pumps. Pumps running is one issue - injecting fuel- as suggested, means the metering pin slots are out of whack with the airplate setting.
Alan