Excessive Cranking on start-up, Assistance request Options

[Van B]

My car doesn't hold pressure for more than 20 minutes, not an l-jet I know, but I suspect it isn't the issue here. Have we gone and checked the spark yet? There could still be something causing weak spark.

I haven’t. But that’s because the only thing left would be the coil and I figure it could manifest itself under normal driving, not exclusively on start up. Plus, it has its own wire again lol

I’ll measure it just to know… and since I’ve measured literally everything else on this car (IMG:style_emoticons/default/lol-2.gif)

[Van B]

Maybe someone with an l jet could comment what their fuel pressure holds at when turned off. Our D jet holds around 20psi for a long time.

my L jet will hold at 20lbs after around 6-7 hours. or did 2 years ago. from somewhere around 28 or so at idle. fuel pump in original position and brand new.

but i know what you are saying emery.
what else draws current. starter?

Mike it takes a few seconds of cranking before I get above 28psi. There’s also no difference in time if I push the AFM flap and watch it build.

I do see the currently draw from the starter in the form of stair steps of fuel pressure building when I’m cranking. But again, no appreciable time difference to full pressure…. Both cases are slow IMO.

[emerygt350]

Just thought I would show you guys what happens when the aar is closed off on a cold start. Behaves quite a bit like low fuel pressure (as in when my pump didn't want to pump). Here are a couple of different starts. My djet cold (35 degrees) at 0 psi fuel pressure (first start of the day). Starts no problem.

https://youtube.com/shorts/q1JS-UG_yDo?feature=share

And then I close the AAR with my little custom troubleshooting device and try to start it. Finally,I open it back up again and do a cold start with fuel pressure.

https://youtu.be/8OJPwwWY_G8

Never touched the pedal during any of this.

[Van B]

Just thought I would show you guys what happens when the aar is closed off on a cold start. Behaves quite a bit like low fuel pressure (as in when my pump didn't want to pump). Here are a couple of different starts. My djet cold (35 degrees) at 0 psi fuel pressure (first start of the day). Starts no problem.

https://youtube.com/shorts/q1JS-UG_yDo?feature=share

And then I close the AAR with my little custom troubleshooting device and try to start it. Finally,I open it back up again and do a cold start with fuel pressure.

https://youtu.be/8OJPwwWY_G8

Never touched the pedal during any of this.

Pfft!!! I wish mine started that quick (IMG:style_emoticons/default/av-943.gif)

[Van B]

Question for the electrical guys:

On the dual relay, I have a jumper wire going from 88z to 88y; which is 12v directly from the battery. When I bought a new relay and replaced all the old connectors, I didn’t have a manual or wiring diagram so, I just copied the existing setup. Now I’m looking at it and I don’t understand the jumper.

Can someone explain what I’m looking at on this diagram vs the actual setup and the potential consequences?

[wonkipop]

Just thought I would show you guys what happens when the aar is closed off on a cold start. Behaves quite a bit like low fuel pressure (as in when my pump didn't want to pump). Here are a couple of different starts. My djet cold (35 degrees) at 0 psi fuel pressure (first start of the day). Starts no problem.

https://youtube.com/shorts/q1JS-UG_yDo?feature=share

And then I close the AAR with my little custom troubleshooting device and try to start it. Finally,I open it back up again and do a cold start with fuel pressure.

https://youtu.be/8OJPwwWY_G8

Never touched the pedal during any of this.

yeah but i can hear your fuel pump priming before you turn the key to crank?
which is your little advantage with D jet.
your up to pressure when you crank even if you bleed down after 20 mins.
do one where you hop in and just crank straight away cold for interest sake. (IMG:style_emoticons/default/beerchug.gif)

my L jet starts almost identical to yours on a cold start.......after a week.
and there is no prime with an L jet.

and my second start of the day if i let it cool down (but the engine block will still be warmish and the aav probably as good as closed still?) is the bam thing your got with the tap shut. except mine keeps going. but its that quick. (IMG:style_emoticons/default/beer.gif) you were doing a super rich start that couldn't go forward?

i see van's got an electrical ? not my territory. though i can see what he has detected.
i've still got a headache thinking through his advancing timing at idle afr riddle. (IMG:style_emoticons/default/smile.gif)

[wonkipop]

@Van B
PS i somehow read a BMW forum last night.
its funny what you drift into.
L jet BMWs.
some guy had a what he thought was excessive cranking at startup problem.
lots of opinion. back and forth.
remedy was installing an in-line check valve after the FP.
he got a result.

not saying that is what it is here.
but he had a pump that would not hold any pressure after switch off.

apparently BMW used to sell a plastic inline check valve for $5.00.
now discontinued.
so he had to buy a more expensive aftermarket valve (probably higher quality).
he had a grizzle about that.
makes you think that BMW had a problem with fuel pumps and worked up a quick fix for a time when the cars were newer.

[emerygt350]

Just thought I would show you guys what happens when the aar is closed off on a cold start. Behaves quite a bit like low fuel pressure (as in when my pump didn't want to pump). Here are a couple of different starts. My djet cold (35 degrees) at 0 psi fuel pressure (first start of the day). Starts no problem.

https://youtube.com/shorts/q1JS-UG_yDo?feature=share

And then I close the AAR with my little custom troubleshooting device and try to start it. Finally,I open it back up again and do a cold start with fuel pressure.

https://youtu.be/8OJPwwWY_G8

Never touched the pedal during any of this.

yeah but i can hear your fuel pump priming before you turn the key to crank?
which is your little advantage with D jet.
your up to pressure when you crank even if you bleed down after 20 mins.
do one where you hop in and just crank straight away cold for interest sake. (IMG:style_emoticons/default/beerchug.gif)

my L jet starts almost identical to yours on a cold start.......after a week.
and there is no prime with an L jet.

and my second start of the day if i let it cool down (but the engine block will still be warmish and the aav probably as good as closed still?) is the bam thing your got with the tap shut. except mine keeps going. but its that quick. (IMG:style_emoticons/default/beer.gif) you were doing a super rich start that couldn't go forward?

i see van's got an electrical ? not my territory. though i can see what he has detected.
i've still got a headache thinking through his advancing timing at idle afr riddle. (IMG:style_emoticons/default/smile.gif)

I don't think I could beat the pump. Tomorrow is another day though!

My AAR opens pretty much every time I start my car hot or cold. My engine runs incredibly cool, not the heads but the rest of it (375 is the hottest the heads get in cool weather, climbing hills 65mph in 5th gear, but that is still warm, haven't had my CHT gauge in temps over 60f yet). On a fresh cold start (35f) you are looking at a good 8 minutes of AAR. After the engine is warm, if I go into a store etc it will give me a minute of upped idle. Hotter the day, hotter the engine the less time but it is still noticeable.

[Van B]

@Van B
PS i somehow read a BMW forum last night.
its funny what you drift into.
L jet BMWs.
some guy had a what he thought was excessive cranking at startup problem.
lots of opinion. back and forth.
remedy was installing an in-line check valve after the FP.
he got a result.

not saying that is what it is here.
but he had a pump that would not hold any pressure after switch off.

apparently BMW used to sell a plastic inline check valve for $5.00.
now discontinued.
so he had to buy a more expensive aftermarket valve (probably higher quality).
he had a grizzle about that.
makes you think that BMW had a problem with fuel pumps and worked up a quick fix for a time when the cars were newer.

I think a check valve is a good idea, but I’m not sure if I trust the rubber lines to live day and night at 30psi.
I need to do the ‘75 SS line diameter from tangerine and my new Bosch pump. Not sure how much faster it will build pressure, but I’m sure it will be a marginal improvement on what I have now based on the specs you posted a while back.

@Superhawk996 can I borrow your expertise to help my understand my wiring question above? I can’t understand why that jumper is there/was put there.

[wonkipop]

oh yeah @Van B.
thats a thought, 50 year old plastic fuel lines just sitting there under pressure silently.

(IMG:style_emoticons/default/blink.gif)

[wonkipop]

Just thought I would show you guys what happens when the aar is closed off on a cold start. Behaves quite a bit like low fuel pressure (as in when my pump didn't want to pump). Here are a couple of different starts. My djet cold (35 degrees) at 0 psi fuel pressure (first start of the day). Starts no problem.

https://youtube.com/shorts/q1JS-UG_yDo?feature=share

And then I close the AAR with my little custom troubleshooting device and try to start it. Finally,I open it back up again and do a cold start with fuel pressure.

https://youtu.be/8OJPwwWY_G8

Never touched the pedal during any of this.

yeah but i can hear your fuel pump priming before you turn the key to crank?
which is your little advantage with D jet.
your up to pressure when you crank even if you bleed down after 20 mins.
do one where you hop in and just crank straight away cold for interest sake. (IMG:style_emoticons/default/beerchug.gif)

my L jet starts almost identical to yours on a cold start.......after a week.
and there is no prime with an L jet.

and my second start of the day if i let it cool down (but the engine block will still be warmish and the aav probably as good as closed still?) is the bam thing your got with the tap shut. except mine keeps going. but its that quick. (IMG:style_emoticons/default/beer.gif) you were doing a super rich start that couldn't go forward?

i see van's got an electrical ? not my territory. though i can see what he has detected.
i've still got a headache thinking through his advancing timing at idle afr riddle. (IMG:style_emoticons/default/smile.gif)

I don't think I could beat the pump. Tomorrow is another day though!

My AAR opens pretty much every time I start my car hot or cold. My engine runs incredibly cool, not the heads but the rest of it (375 is the hottest the heads get in cool weather, climbing hills 65mph in 5th gear, but that is still warm, haven't had my CHT gauge in temps over 60f yet). On a fresh cold start (35f) you are looking at a good 8 minutes of AAR. After the engine is warm, if I go into a store etc it will give me a minute of upped idle. Hotter the day, hotter the engine the less time but it is still noticeable.

we are all homing in on that 8 minutes.
your emprical evidence.
and some old kombi bus wisdom i dug up on a very old website.

[Superhawk996]

@Superhawk996 can I borrow your expertise to help my understand my wiring question above? I can’t understand why that jumper is there/was put there.

Let me preface by saying:
1) I have not played with L-jet and/or the dual relay.

2) My car was a 73' D-jet so I have no parts for physical comparison.

After some scholarly study of the current flow diagrams for 74/75 L-jet just to understand how they are wired . . . . I have no idea why pin 88y and pin 88z would be jumpered.

According to the diagram you posted as well as the Haynes manual diagrams, I read this as within the double relay (J40) pins 88y and 88z are already internally connected and both would receive 12v power from the battery (A).

Is it possible that the double relay you have isn't the OEM 914 part and maybe the internal jumper between 88y and 88z isn't there?

You can do a continuity check between pins 88y and 88z with a DMM (remove the 12v battery feed 1st) to see if the internal continuity is there.

There would be no adverse consequence to the jumper since it would be a parallel path to the internal jumper. I'd get rid of it assuming the internal continuity exists between pin 88y and 88z. No point in a redundant external jumper.

@Van B

[Van B]

@Superhawk996 can I borrow your expertise to help my understand my wiring question above? I can’t understand why that jumper is there/was put there.

Let me preface by saying:
1) I have not played with L-jet and/or the dual relay.

2) My car was a 73' D-jet so I have no parts for physical comparison.

After some scholarly study of the current flow diagrams for 74/75 L-jet just to understand how they are wired . . . . I have no idea why pin 88y and pin 88z would be jumpered.

According to the diagram you posted as well as the Haynes manual diagrams, I read this as within the double relay (J40) pins 88y and 88z are already internally connected and both would receive 12v power from the battery (A).

Is it possible that the double relay you have isn't the OEM 914 part and maybe the internal jumper between 88y and 88z isn't there?

You can do a continuity check between pins 88y and 88z with a DMM (remove the 12v battery feed 1st) to see if the internal continuity is there.

There would be no adverse consequence to the jumper since it would be a parallel path to the internal jumper.

@Van B

@Superhawk996 Thank you very much for the confirmation that I'm not losing my mind. The dual relay I have is the updated plastic Bosch part and not the old metal housing. But everything is the correct configuration. Now that I have the above diagrams I started looking at it when I did the fuel pump wiring just to make sure everything is correct, and that jumper was melting my brain. Granted I was begging the question a bit by concluding "there must be a reason", but as it turns out, I don't see a legit reason. The only possible explanation is if they aren't on the same circuit for this particular relay.

So, I'll give it the tone test with the MM before I cut the jumper, per your advice.

Thanks again,
Van

[Superhawk996]

So, I'll give it the tone test with the MM before I cut the jumper, per your advice.

Thanks again,
Van

Can you post a picture? I'd love to see this.

Is the jumper a home brew add on or is the jumper part of the OEM wiring harness / plug connector? Could it be possible the wiring diagram are simply showing the jumper as internal even though it is part of the harness?

@Van B

[Superhawk996]

Found this while Google'ing for pictures of the 914 double relay harness. Good general description of the operation and a re-drawn schematic that some might find easier to read. Be warned -- This is for VW Bus so not Exactly the same.


https://ratwell.com/technical/DoubleRelay.html

[Superhawk996]

@Van B

Found this on Restoration Design site for 1.8L L jet. Looks like it has a jumper so maybe that connection between 88y and 88z is not internal to the relay as drawn in the wiring diagram.

DMM continuity check will tell you for sure.

[Van B]

I'm pretty sure there used to be a block plug on it, but when I bought the car it was block plug on the FI side and then individual wires on the main harness side. The plugs were all beat to hell and corroded so, I redid everything to make it all tidy.

I'll take a picture tonight and tag you so you can see it for yourself.

PS, that ratwell article shows the relay that I have. But his hand drawn diagram doesn't make sense to me. The numbers seem all wrong.

[Superhawk996]

I'm pretty sure there used to be a block plug on it, but when I bought the car it was block plug on the FI side and then individual wires on the main harness side. The plugs were all beat to hell and corroded so, I redid everything to make it all tidy.

I'll take a picture tonight and tag you so you can see it for yourself.

PS, that ratwell article shows the relay that I have. But his hand drawn diagram doesn't make sense to me. The numbers seem all wrong.

Picture will be great. I've always had 73's so no optics on L-Jet. I'd like to see it.

Agree on his numbering. I think what he was trying to do is to show that the dual relay could be replicated by wiring up two conventional Bosch SPDT relays. He's using Bosch conventional numbering for relay pins 85 & 86 are solenoid, pin 30 is the power feed. Strangely, he doesn't label Normally Open output 87. (IMG:style_emoticons/default/confused24.gif) Likewise, he doesn't really help with specification of values for the current limiting resistor or the diodes. (IMG:style_emoticons/default/confused24.gif) Numbers to the ECU pins will also be different because that info is for the Bus ECU. i found it interesting just for general info, and theory of operation. Good overview about how the L-Jet uses the dual relay arrangement to energize the fuel pump during cranking and then once running, how it "latches" via the Air Flow Meter circuit and how it deactivates fuel pump if engine stops running.

For me, I'm not a fan of the late model current flow diagrams. Yes, they have some advantages, but, I was taught by USAF to read schematics so those are easier for me to "see" the circuit. I think that was mostly why he drew it that way.

@Van B

[wonkipop]

had a look at mine @Van B

think we have that same black plastic relay.
i can't see any jumper wire on mine.
wires coming in but nothing that i can see looks like a jumper wire across.

bit hard to see and take photo of.
would have to unbolt it to get a good look.

[wonkipop]

best i can do with photos unless i unbolt.
thing is impossible to get a shot of.

there is a red wire, but as far as i can see at moment doesn't look like a jumper.
seems to feed into loom.