3.2 Carrera Fuel Pump Question?

[scarceller]

I have a 84 Carrera and was wondering if anyone knows if the fuel pump in the Carrera should run for a moment when the key is turned to 'Run' position right before you go into 'Start' position?

In my car the pump does NOT start to run till you go into 'Start' (Crank). The DME seems to signal the Fuel Pump relay to close and this does not happen till you are in key 'Start' mode. Many other cars turn the pump on for about 2 seconds when the key goes into 'Run' (just before 'Start'), this allows for fuel pressure (FP) to come up so by the time you go into 'Start' you have plenty of FP behind the injectors. Doing this makes for very quick starts ussually on the first crank or 2.

Basically, in my car my pump works OK and delivers fuel as per spec but during starting it take about 5 - 7 cranks to start. So I decided to look at FP with the car dead cold and starting. The result is I don't get solid 2.5bar till about the 2nd crank. Then on another day with the car dead cold I jumpered the pump fuse at the fuse box so that I started the pump for about 2 seconds before I tried to 'start'/crank and the car fired up on 1 or 2nd crank. Could be the pump is getting old.

I'm thinking of coming up with something to trigger the pump for about 2 seconds before entering 'Start' mode.

I think the Carrera simply does NOT turn the pump on till you are in crank. Just wish to confirm and see what others have to say.

Thanks.

[scarceller]

I did a quick review of the Fuel Pump wiring and circuit and I found that the ignition switch 'Start' position feeds 12V to the starter (relay, pin 50) and this same line is feed into pin #4 of the DME.

Then in the DME schematic it shows pin #4 wired to a Darlington transistor's 'Base' this in turn activates the transistor and then the transistor simply grounds pin #20 of the DME, this pin 20 is wired to the Fuel Pump relay and closes the relay causing the pump to come on.

If I'm reading everything correctly it looks like the Fuel Pump is designed to run in start mode.

But, one other interesting thing is that the Darlinton transistor that drives the Fuel Pump relay also has it's 'Base' wired to the digital circuit board of the DME. It seems to be driven by pin #3 of the main 8051 processor chip, this pin is an I/O pin so it could certainly drive the pump on. Not sure why this is? but it seems like the 8051 could also turn the pump on. Anyone know about this pin #3 on the 8051? We need someone that knows the 8051 program logic to comment on I/O pin #3 and how it is used by the DME program logic.

Thanks.

[jcunning]

Would this second circuit keep the fuel pump running after the engine starts and the key goes back to the run position?

Another question:
Many people doing a 3.2 swap into older cars say that the yellow wire (DME pin #4) is not needed to start and run the engine. Based on your analysis, it looks like this is true as the 8051 will still power the fuel pump.

[scarceller]

I think you may be correct. I have concluded that the Darlington transistor that drives the fuel pump relay is driven by 2 signals.
1. One is 12V from on pin #4 of the DME which comes from the ignition switch 'start' position.
2. The 8051 I/O pin #3 can also turn the pump on.

This does indicate that the pump is first turned on by the key in 'Start' but then once it goes into 'Run' the 8051 must take over via pin #3.

The question I have is do these pumps ever turn on for a few seconds when you first go into 'Run' just prior to going into 'Start'? My car does not, but it would be nice if it did as this would help start the engine quicker by insuring the injectors had solid 2.5bar FP just prior to start cycle.

Originally Posted by jcunning

Would this second circuit keep the fuel pump running after the engine starts and the key goes back to the run position?

Another question:
Many people doing a 3.2 swap into older cars say that the yellow wire (DME pin #4) is not needed to start and run the engine. Based on your analysis, it looks like this is true as the 8051 will still power the fuel pump.

[911quest]

The pump does have a check valve it might not holding pressure....

One thing that some newer european cars do is as soon as the drivers door is open the pump runs enough to make sure the system is pressurized.

[scarceller]

Tony,

My pump is not new, but the check valve passes the FP system test. It holds pressure above 2.0bar for at least 30 minutes or more. So my valve is not shot. But my pump may very well be getting on in age and most likely does not deliver pressure as instant as a new one would.

I'm certain that these cars when NEW fired up on 1 or 2 cranks.

The idea is could we somehow modify the Fuel Pump circuit so that it activates the pump for about 2 seconds when key goes into 'Run'?

The idea is to slightly improve the start cycle.

Originally Posted by 911quest

The pump does have a check valve it might not holding pressure....

One thing that some newer european cars do is as soon as the drivers door is open the pump runs enough to make sure the system is pressurized.

[jbrinkley]

the pump does not turn on until the key is turned.
I say that based on what other carreras around town do, the bosch manual, and my own messing around.
I replaced mine with a new one when I did the turbo thing and noticed a quicker "catch" time.
I use to listen to mine from the fuse box, and did this when i started it after a long stretch when pressure bled off.
One thing I will say say is that with a new pump I didn't have any pressure changes compared to the old, which is as expected. I just noticed a quieter pump and quicker charge time, with the lines empty. New injectors are also quieter.
and i found a lizzard just now when I took this picture

[jcunning]

"The idea is to slightly improve the start cycle."

So, you just need to modify the DME Pin #4 power wire to supply a 2 second power burst at the right time.

You could use a relay and trigger the fuel pump on this pin.

I'm not sure if they make a timed relay that only fires once and then stops.
Maybe someone else can chime in. You might be able to use a blinker relay, but I'm not sure how to make it stop after one cycle.

You could use the door open wire (kinda dangerous in a rollover), or you could use +15 line to trigger the relay.

[scarceller]

Thanks for the feedback, I guess the Carrera is designed to turn the pump on during 'Crank' mode.

But you seem to indicate that jumpering the pump early (after a long storage) does help.

So, would it be a good idea to figure out a simple circuit to always do this? Have the pump come on for 2 seconds or so when the switch hits 'Run'? I'm going to poke around in the DME schematic to see if maybe we already have some signal that goes hot for a moment when the DME is first powered up by the 'Run' position.

What do you think?

Originally Posted by jbrinkley

the pump does not turn on until the key is turned.
I say that based on what other carreras around town do, the bosch manual, and my own messing around.
I replaced mine with a new one when I did the turbo thing and noticed a quicker "catch" time.
I use to listen to mine from the fuse box, and did this when i started it after a long stretch when pressure bled off.
One thing I will say say is that with a new pump I didn't have any pressure changes compared to the old, which is as expected. I just noticed a quieter pump and quicker charge time, with the lines empty. New injectors are also quieter.

[scarceller]

Building a timer circuit is really simple. But I'm going to poke in the DME schematic to see if we may already have such a signal we could use.

I really think a quick alteration like this would help cold start on these older cars. Test it for yourself by simply jumpering the FP fuse (like jbrinkley shows in his picture above) before you try to start the car. For me this really helps my start cycle.

Originally Posted by jcunning

"The idea is to slightly improve the start cycle."

So, you just need to modify the DME Pin #4 power wire to supply a 2 second power burst at the right time.

You could use a relay and trigger the fuel pump on this pin.

I'm not sure if they make a timed relay that only fires once and then stops.
Maybe someone else can chime in. You might be able to use a blinker relay, but I'm not sure how to make it stop after one cycle.

You could use the door open wire (kinda dangerous in a rollover), or you could use +15 line to trigger the relay.

[jbrinkley]

I wanted to run a switch on the dash, just a simple one to run the pump for a second or two.
But that seemed a little invasive, I have enough on the dash already and it just doesn't seem like a must have.
*one thing I did consider, and actually have sitting here is another check valve I could put in line on the return side of the fuel lines, (after the rail near the stock FPR)
This would keep positive press on the rails and in the line all the way back to the pump, and might make a car catch a few cranks earlier relieving the starter. My concern was volume though, so I didn't.
Again that would be a fix for something that shouldn't be broken, it's just a long way from the pump to the injectors. If you listen to a pump push fuel through empty lines, it takes a long time for the return fuel to make it back to the tank, if you get my meaning

[scarceller]

jbrinkley,

I tend to agree, would be nice to have those injectors fully pressurized before you go into 'start' mode.

Another thought would be to have someone comment on I/O pin #3 of the 8051 processor. I have a funny feeling that the code could be altered so that it does this for us. Simply alter the code so that it drives the a signal on this pin for 2 seconds when the DME sees 'Run' mode. The later DME boxes (87-89) have the program in the 8K chip along with the maps. So for those later 8k chips it could be done by getting a new chip.

This would be a great feature for custom chip folks to include in the chips they sell. Where are you Steve Wong? for me it won't help cause I have old 4K DME and the Program is not in the EPROM chip.

Originally Posted by jbrinkley

I wanted to run a switch on the dash, just a simple one to run the pump for a second or two.
But that seemed a little invasive, I have enough on the dash already and it just doesn't seem like a must have.
*one thing I did consider, and actually have sitting here is another check valve I could put in line on the return side of the fuel lines, (after the rail near the stock FPR)
This would keep positive press on the rails and in the line all the way back to the pump, and might make a car catch a few cranks earlier relieving the starter. My concern was volume though, so I didn't.
Again that would be a fix for something that shouldn't be broken, it's just a long way from the pump to the injectors. If you listen to a pump push fuel through empty lines, it takes a long time for the return fuel to make it back to the tank, if you get my meaning

[jbrinkley]

I have a 4k also and a different chip completely

I bet steve would fix you up though, he has the 4k to 8k stuff on his site.

[scarceller]

OK,

So here's an idea:

Use the idle stop microswitch signal to run the pump. This signal goes into the DME on pin #2. When you are in 'Run' and the throttle plate is closed the switch grounds pin #2. But if you are in 'Run' and just slightly step on the gas pedal the switch opens and takes the ground off the pin #2.

You could use this procedure to activate the pump: Turn key to 'Run' tap the gas pedal and the pump runs so long as the pedal is slightly depressed.

The issue that has me worried is I still would only want to run the pump for 2 seconds or so and only when car is not running.

Have not thought this through all the way yet, and I'm concerned about saftey if you are in an collision.

[CruiseControl]

Many may not agree with my thoughts on this, but my preference on engine starting is to provide some oil pressure on cranking before firing the engine. 9 psi at 160rpm cranking for 3 sec must be better than nothing.
Paul

[scarceller]

Interesting theory, so what's better:
1. a quick start on first crank?
or 2. start a few cranks late and let oil pressure build up?

Now you got me thinking???? maybe it's not so bad to start a few cranks late.

I'm sure others will chime in here.

Originally Posted by CruiseControl

Many may not agree with my thoughts on this, but my preference on engine starting is to provide some oil pressure on cranking before firing the engine. 9 psi at 160rpm cranking for 3 sec must be better than nothing.
Paul

[WI wide body]

Not sure about the 3.2 engine in my '86 Carrera but I do know that all the old timers (that now includes me) told me that my 1969 Triumph Bonneville should ALWAYS be kicked at least 9 or 10 times before firing it up so that the oil would get up to the shafts and rockers and other critical points.