I've read some helpful things here while helping with my brother's '72 914. I think I've learned something new and thought I'd share it with you guys.

This car has the original engine and FI system, though the ignition system has been updated and is electronic. The car wasn't running well, and the local shop my brother uses said he should do a carb conversion, costing over $4,000. We looked online and found some good write-ups that recommended keeping the FI system. I've worked on many cars and restored one, so I thought I'd try to get the car running well enough with the original system.

The compression and ignition checked out fine. We adjusted the valves (of course). We tested and then replaced 3 injectors, and the CHT sensor. I put the fuel pressure at 28 psi, per spec. Static tests of the manifold pressure sensor came out fine. A cigar smoke test showed no intake leaks. We cleaned and adjusted the TPS, and then finally changed the TPS contact plate and adjusted the arm (when the car just wouldn't run right). All the other components checked out fine, using tests I found online.

The result? The engine fired right up, with a good idle. But when driving it lacked power, and the higher the rpm the less it wanted to pull. (Not right for a Porsche.) It felt like the timing wasn't advancing, or that the engine just wasn't getting enough air or gas in the right balance.

Other than buying a replacement MPS or computer, I was running out of ideas to try. One of good things about carbs is that they are adjustable. One of the challenging things about these old open-loop FI systems is that they are not really designed to be adjusted much, or at all. Repair is usually a process of testing and replacing components. But this car sure felt like it needed some kind of adjustment.

One of the odd things about this car, in my experience, is that the fuel pressure regulator IS adjustable. So that's what we tried, just using seat-of-the-pants performance as the indicator. We dialed the pressure down a turn and things got worse. Then we turned the pressure up, one turn at a time, and voila! As we did the car ran better and better. Now it pulls in the upper ranges like it should, much like it used to.

Now we're going to buy a 4th injector of the same type and adjust the pressure again as needed. (Now that we know we can adjust the whole system.) Perhaps that will make it run better still.

I haven't read that anywhere(about adjusting fuel pressure to get the engine to run better) so I thought it might help someone else who is struggling with these old Bosch systems.

Happy motoring!

Richard

Thanks Richard for the writeup. When Fat Performance built my 2.0L motor with a slight (80cc) increase in displacement, they suggested that I might need to increase the fuel pressure to get the most out of the motor but I couldn't find any reference to anyone doing this, so I was a bit unsure if I would benefit from do it and no longer having a FPG to read the pressure unnerved at shooting in the dark.

So, let me ask a question. Would I be correct in guessing that looking down on the adjustment screw turning clockwise (screwing in) would reduce pressure and turning counterclockwise (screwing out) would increase pressure?

Thanks again mate, and

Brady

Brady,

I found the opposite to be the case. Once you have loosened the locking nut buy a few threads (13mm nut, I think), then you turn the bolt in, clockwise, to increase pressure, and out to decrease pressure.

I had a pressure gauge on it when I first made the adjustment. It wasn't real sensitive to small turns. When I made adjustments this time, I did it in whole turn (360 degree) increments (corresponding to a thread on the bolt).

And of course, one needs to re-tighten the locking nut when done.

(Ive read that one can make small mixture adjustments with the knob on the ECU, which I have not tried yet. But those adjustments are supposed to only affect the mixture at idle. Not sure about that, but I'll try it too.)

I hope that helps.

Did you clean your distributor? And put of drop of oil ont eh advance plates?

I agree that adjusting the fuel pressure works. After I rebuilt my son's 1.7,I checked the fuel pressure. It was 28# so I increased it to30# by adjusting the pressure regulator. Now that baby really screams! It's an early 1970 model year, so there is no adjustment knob on the computer unit.

Thanks. You're right. I should do that too. The timing on this model is set at a higher rpm (2000 or so if I remember right), and we did that. But timing could still be an issue at upper rpms.

Timing set at 27 deg advance (with vac lines disconnected) at 3,500 RPM

Several years ago a local gave me a ride in his '74 L-Jet; it screamed like no stock 914

He had increased FP to 43#, adjusted the WOT at the AFM, and reamed out the TB
Felt like a -6; stock P&Cs to boot

The adjustment knob on the later ecu.s only affects the idle circuit and not the injector pulse duration.

THX. I remember now. That's what we did. Though it was a first for me, to set (or rather to check) timing at that high rpm. One of the benefits of electronic ignition was that it didn't need to be adjusted.

Sweet! Exactly what I needed to hear. Right now I'm only about 20 miles into the break-in so I'll not be running it to high revs until I do the 1,000 mile oil change and valve adjustment but may start playing with the FP a little bit here. I would think the real value of an increase in FP would be at higher RPMs as the demands on fuel delivery increases so the real tale of the tape will come later.

Man this 914 stuff is fun! Might have to get another one!

With all the alcohol in what they call gas, you need to increase volume by 10% I agree with the fuel pressure @32 PSI made my 2.0 run like a champ and lowered temps.

Am I correct ? Certain year Pressure Regulators at NOT adjustable ?

I need to buy a fuel pressure gauge. What model do you guys recommend? The choices I'm running across have mixed reviews and the prices are all over the place.

It is the problem.
They get sticky when hot, remove and replace the grease between the advance plates.
It's not a Porsche power band, it's vw.
You will feel power drop at 4800 rpms....that's all you get...
There are dyno charts here somewhere.

Clean the advance plates, you are almost done!

The one at HF works fine.

By chance you have a link to buy it? (in other words, who's HF?)

Thx

HF = Harbor Freight. You can't be a card carrying CSOB 914 owner without knowing that.

http://www.harborfreight.com/fuel-injectio...ster-62623.html

Cheap stuff. In general , don't buy anything there you REALLY need to last or work well.

So THAT's why my CSOB 914 Member card hasn't arrived yet! I been wondering 'bout that.

Thanks, I'll check it out.

OK. I'll check and prob clean the advance mechanism. Thanks.

Moving now from facts to personal opinions... I have a pressure gauge but I probably won't be using it for this anymore. For starters, it's a pain to do and usually gets some gas in the engine bay. Second, it's real easy to take a couple of wrenches with me, go for a test ride, and tweak the fuel pressure at stops along the way.

When making the mixture richer, with higher pressure, my plan is to take it only as far as it makes a noticeable difference. No further. And I plan to check the plugs relatively soon to make sure that setting isn't too rich overall.

Basically, I think every mechanism works best with some form of adjustment. The more complex the mechanism is, the more it needs it. None of these engines are new, and the components have unknown degrees function, misfunction, and variation. Modern closed-loop systems adjust for those variables constantly. These old cars are the opposite of that.

I don't know whether the engineers at VW/Porsche planned for the adjustable fuel pressure regulator to be used this way or not. (I suspect not). But for a car this old with this many variables, having an effective adjustment capability sure helps!

You should be tuning by adjusting the MPS not the FPR.

I was waiting for this. I don't buy the idea that you can just turn up the fuel pressure above what it's supposed to be and get magic power. If that actually works, something else is out of whack. It needs to be tuned properly.

I'm in total agreement here. My interest in increasing FP is not to compensate for something being wrong nor to increase power with this adjustment alone but rather something being out of balance. It's possibly out of balance because of the increase in displacement in my rebuild. I don't expect there will be very much of an increase needed and I'm sure it will only be evident at higher RPMs, which I won't see for the next 1200 miles or so after the break-in period however, the factory set the FI for the original engine design and I am bumping up the displacement. So, I will at least play with it and will of course relay any improvement or lack thereof back to the board. I'm not looking for magical increase in power, I'm looking to insure that if the injectors need more fuel at higher RPMs that it's original programing dictated then the FP adjustment will deliver. I want to adjust the feed to match the need.

... then again I could be wrong, it's happened before, though not often (hehehe) unless you ask my wife, she seems to think I'm wrong way more often than I do. Go figure

You said it was a stock motor.

You didn.t mention anything about increased displacement or that you had rebuilt it.

If you increased the displacement you need to tune the MPS
If you have never cleaned advanced plates, it really needs to be done or you will chase your tail.
If you opened the case it is possible the camgear is not set properly
You can add a variable resistor (1000 ohm volume knob) inline with the CHT and keep turning and driving till it respond how you want.
This is a bit of a hack, when you like how it runs, check the resistance through the volume knob, then go buy a resistor of that size and put it inline forever. This will increase the fuel across the whole range, so idle will suffer

I am not the original poster and you are correct that he did not say anything about an increase but I was chiming in with my own separate interest in playing with the FP

Sorry to confuse

Thank you, all. I appreciate the input.

My reactions, for what they're worth:

First, we don't know that the MPS needs adjusting. It might. Probably does. It's only 45 years old. I wish I could do it easily. From what I've read, I doubt I could do it thoroughly or well, even with a lot of effort. (Taking it apart sounds like a daunting task.) If someone has a good way to adjust it and test it properly, without running the risk of screwing it up, I'd love to hear it. In short, if I can get the car running well enough without risking the MPS, I'll probably do that.

Second, even if the MPS could use some adjustment, I don't agree that I shouldn't be adjusting the fuel pressure. We don't know how accurate my cheap pressure gauge is and at this point I don't think it matters. The pressure that worked best on a new car in the factory in 1972 might not be the pressure that works best on this particular car, with this mixture of old and new components, some original and some after-market. I see the 28 psi as a starting point for the tune, not necessarily the right end point.

Third, I will check the advance mechanism (weights and vacuum). Easy enough and worth doing. I'm skeptical of the benefits it will show, however, because of the way the timing is set for this engine (at 3,000 rpm). Clearly the centrifugal advance is working well enough for that, so the timing with the hoses connected shouldn't be far off, if it's off at all.

Again, thanks all. I'll report back with more results when I have them.

Clever hack about the volume knob. I get it. Might give it a whirl. I could even put the volume knob in the cabin and adjust it on the fly. Try different settings before and after the car warms up, to find the right balance. Thx.

The weights stick when the old grease gets hot, then say after you wind it up at a stop sign and the centrifugal force overcomes the sticky grease the weight get stuck at full or partial advance and when you shift up, the timing is now terrible for the lower rpm and the car bucks, sometimes quite a bit.

It will keep you chasing your tail for a long time, cost hundred of dollars in parts. Or you could do it and spend 0.05 on grease. I just use normal bearing grease. And I have found it on every car I have touched....quite a few.

The CHT
In 73 the factory used a resistor inline on the 2.0 liter models to enrich that specific year. I used a volume knob because I could drive and tune....takes maybe 30 minutes to simulate all conditions...load, no load, accel, coast on highway . I planned a route to radio shack, measured the switch when I got there and replace it with the resistor....same route home to verify results. Good for years (that car, that elevation...)

I too changed fuel pressure (it was the distributor weights ) and that screws up idle and makes a hard start sometimes. 28 is the right number old or new motor, leaky or not. The mps and CHT control the duration of the injector opening....those are the keys.
If the mps holds a vacuum properly I would look elsewhere, but not fuel pressure.

Lastly, I removed my cold start injector from the loop, wiring and fuel..... those drip quite a bit and can make tuning hard.

Also, the ONLY vacuum line required to the plenum is the mps. I get rubber pipe caps at the hardware store and remove and block off every vacuum line at the plenum. Drive it. Then add one single vacuum line back, drive again.

You have to leave the mps hooked up, but you test it and make sure it's not leaking.
The test for me is i suck on the hose and if it sticks to my tongue it holds a vacuum....move on.

The cap'n would have thoroughly chewed ass here. If your guessing at the pressure it might be 35 lbs or even 40. That will quickly destroy parts of your system. Injectors will be the first to suffer. They will start leaking internally flooding the combustion chamber, and possibly washing the cylinders and damaging the rings. Then they can leak externally and possibly burn your car to the ground. Many very knowledgeable people here have told you it's a bad thing, but you continue to ignore them. Good luck with car.

Thanks!

Sorry Captain, but you won't be hearing any fire engines racing to this house.

(I'm not an idiot. I used a gauge when I first adjusted the pressure, so I saw how sensitive the adjustments are. It was at 32 when I started. I turned it down to 28, and the engine wouldn't pull at upper rpms. I turned it back up a bit, probably in the 30-32 psi range, and it ran great. No fires. And clearly the ignition advance is working or it would not run well at higher rpm.)

That's all. I said the car was running well. Still is. I was just putting my experience out there in case it helps someone else.

For those of you who still think I should adjust the MPS, I'm eager to hear how you would do that. Mine holds a vacuum fine, and it passes the static electronic tests. And again the car is running pretty well. I'm reluctant to tear into the complex and fragile MPS when things are working, but I'm open to suggestions (like the variable resistor idea on the CHT).

Thx.

Buy the mps tuning kit from Chris Foley. I believe it comes with instructions.