Official Fuel injection questions thread

[PuddleRainbow]

Hello, While hamfistedly dropping my motor, I broke one of the vacuum can (Can: 07 114)nipples on my 043905205H distributor (76 beetle)I would like to buy another vac can but can’t find one currently listed. Does anyone know of a adequate substitute that will work?

Or a decent performing SVDA I can replace the original? The retard function has probably not worked for decades anyway. I’ve been timing it like a SVDA anyway.

Thanks.

[MuzzcoVW]

I have used a generic single vacuum unit that I believe I bought from aircooled.net, or one of the like suppliers. It works very well. Not having vacuum advance working on these ,especially the F.I. engines make them a dog driving around town.

[busdaddy]

I've glued vacuum nipples back on to cans using JB weld, or that 2 part epoxy putty you mash together to activate, no "generic" replacement will work like the real thing, even if the retard is FUBAR.
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[MuzzcoVW]

[PuddleRainbow]

Thanks very much. I’ll try the epoxy first then nab a can if that doesn’t work. The nipple is still in the can but loose so I may have a chance. Will let you know.

[bug1000000000]

So with idle issues on my 78 Vert, I did the test of the Aux Air Regulator's two electrical contact and found the meter go to infinity. Bentley calls for replacing it, so now that a used one arrived from Ebay, the testor also shows no resistance. Is this the absolute test that the unit is bad?
Your help will determine me returning it and asking for a refund.
The Bus Depot has a new one for $200 and a $60 core charge. Ouch!

[busdaddy]

If there's no resistance it's a problem, I assume you know how to use an ohm meter?, have you tested the meter on something else like a light bulb to confirm it works?
You can try connecting 12 volts to the terminals (polarity doesn't matter) and watching the opening through the hose ports for movement, it should also start to feel warm after a little while.

It's pretty rare for 2 of those to both be bad, they are usually very robust. There's a number of them in the classifieds, bus ones are the same part. https://www.thesamba.com/vw/classifieds/search.php...ton=Search
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[bug1000000000]

Here's one forum's idea of checking the AAV...

"Remove the valve. Hook up the heating eleloment tereminals to the battery. Watch thru the valve to see if it closes off tight. Aim it at something bright or a light to see it best. It takes about 5 minutes to fully close. Does it rattle? Does the disc slip arround? If so it's broken.
Caution: when shaking it the return spring on the disc , if loose, may short out the terminals. Sparks fly!! That also means it's bad."

What do you think?

[busdaddy]

Pretty much what I was describing, aside from the shaking, if it rattles it's not a good sign either.
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[bug1000000000]

Thanks busdaddy!
Was typing similar thoughts to yours at the same time.
Will try watching through the port with 12v applied!

[krisbeetle]

I think I'm down a little bit on power going up hills and when accelerating in 4th gear.
It's hard to to tell for sure.

I have 25 psi at idle and can get over 30 psi when reving it up. Pushing in the afm all the way I can get 35 psi back to the injectors.

If you were going to look for something that felt like a 10-20% power loss where would you look?

In first when you stomp the throttle it feels like it has lots of jam. In 3rd it seems like a big jump going to 4th and can feel a bit of lack of power.

It can go up a steep grade at 50 mph which isn't too bad.

[busdaddy]

I'd be investigating the vacuum advance system as well as the rest of the distributors mechanicals, sounds like your fuel pressure is within spec. Although driveway testing doesn't mimic under power like third gear + demands, it might be fuel filter time. Another place to look would be the TS2, good thread and wire connection contact?, Ohms match what's in the AFC manual?

Pushing harder on the AFM flap is not a way to test fuel pressure, it increases the time the injectors open by a few milliseconds, but unless the engine is consuming it under power it's not going to tell you much, the fuel is still circulating in the system the same way. Fuel pressure tests are usually system pressure, system pressure with vacuum applied to the FPR and max pressure with the return line pinched. You'd be better off testing flow to see how fast it can fill a gallon jug, or running the pump for 10 minutes + (system connected normally) and watching for a pressure drop.
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[krisbeetle]

I also have 1/4 inch fuel line running from tank to fuel filter before pump. Is this going to be a major problem vs the 7mm fuel line ? It was hard to source local.

It's not much smaller but would that be enough of a restriction? Think it's like 6.8mm vs 7 mm

Would it be better to attach a fuel injector into a jar and measure how much comes through each injector in a set time?
Would I try to have the afm flap fully open then?

Just not sure what would fully replicate under load uphill/ 4th gear accelerating.

[busdaddy]

The slightly smaller line shouldn't make a difference. Some of what you describe can be caused by a dirty filter, or crap floating around in the tank and partially blocking the outlet.
Testing flow at an injector is a really precise job, if you send them out to Witchhunter, or take them to your local Bosch diesel injection shop they can clean and flow test them, the local shop usually does it same day.

But....., since you say it runs great at low speeds and in lower gears I doubt it's an injector issue, it's only happening under big load (HP required to go faster increases exponentially). The possibility I'm leaning towards is enough fuel is getting into the system to make good pressure at idle and lower speeds, but as demand increases it can't keep up the supply compared to what's being consumed.
A drive with the pressure gauge tapped in to the system with a long hose and positioned where you can see it in a mirror (or have a helper watch) might offer some insight when it starts losing power.
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[VW_Jimbo]

Agree with the above. BUT..............

What does the spark look like? Weak spark means incomplete combustion and a lack of power. It is typically felt under load, as the demand with a richer mixture is harder to combust than a leaner one.

I just went through this myself. I chased a sluggish feeling at higher RPMs and under load, intermittently. I tried everything to test while driving it. Either I could not test it, due to the randomness of the issue. I then started tightening wire connectors. Still nothing. Out of desperation, I decided to start changing components, one at a time, to determine their effect. Changed the fuel filter first - nothing, air filter - nothing, disconnected the PCV tube - nothing, changed the cap and rotor - nothing, plug wires - nothing, whole damn distributor - nothing, spark plugs - nothing, spark plug wires - nothing, rebuilt the carbs - nothing, adjusted the valves a hundredth of an inch in either direction - nothing. Sitting in the garage, staring at the engine, asking the repair Gods to shower me with some of their wisdom and BAM! The coil! It tested good, Ohming it. It had great spark under NO LOAD. But I had no way to test under load. So, I swaped it out with a known good unit I had.

BAM!!!!! That was it, weak spark! Been riping the streets up since then!

BTW, off the car, the coil tested 100%. Took it to a buddy's shop. Installed it on one of his many Bugs and set it up on the O-Scope and his dyno. Perfect wave form with no load. Even slight load had no issue. Got it up to the 3500 RPM on a dyno with a slight load, and that is when it would intermittently switch to ground, then toggle back to normal, then back to ground, until it either went above 3600 or below 3500. I do not understand why or how, but I do know I could see it happen!

I would try a new coil. Not a Bosch one, but a PerTronix Flamethrower. They are way better units!
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There is never enough time to do it right the first time, but all the time necessary the second time!

[busdaddy]

I agree, that's why I suggested some distributor probing first And then we went down the fuel pressure Vs: AFM flap position rabbit hole Could also be a condenser or wire issue.

If one wasn't feeling all that mechanical, or wasn't confident they were doing it right they could get in touch with Bill and have the distributor serviced: https://www.thesamba.com/vw/classifieds/detail.php?id=2235472 , money well spent on a 42+ year old car, and it'll rule out one major possible cause.
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[krisbeetle]

I'll have to get ten feet of hose. ... when I would blip to to WOT real fast and off again at idle it would jump up instantly to 35 psi...

Would plug wire orientation matter? As to location on cap vs timing of injector?
Or if I remember it doesnt matter because injectors all fire at once?

[busdaddy]

Wire location doesn't matter as long as the one that's over the tip of the rotor when the points open leads to the cylinder that's coming up on firing TDC, if you had them wrong it wouldn't run at all. Timing does matter though, if your vacuum advance is janky, or something is sticking or wobbling it could effect power.

A quick blip of the throttle should make the pressure jump (vacuum drops), that means the FPR works, but it still can't simulate consumption under heavy load.

Maybe instead of a long hose you can set up a Go pro or phone near the gauge and record the readings?, the challenge would be knowing when to look as it was acting up, maybe beep the horn so you hear it on the soundtrack as you watch?
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[krisbeetle]

One onjectir hold down bolt backed off a little... luckily it hadn't seen more ths a couple km before I found that... that added some torque for sure...

I swapped in another coil... didnt make much difference.



It feels pretty strong honestly.... I've never had a fi beetle before... I looked for hp numbers but are they the same as a 74 34 pict non smog standard bug in power to weight ?

The motor runs really good... It honestly feels like about 5 hp difference from 74 standard with a fresh motor...

[krisbeetle]

What size is the fuel line going from tank to fuel filter? And then fuel filter to fuel pump?


Also I saw someone say on here that the steel line going through the body of the car is 6mm OD, is this true ? And what is the ID of the steel line?