1970 EFI strange issue

[dailydrivervw]

1970 efi in my daily squareback, has finally got to me.. after 11 years.

It starts to break up, die out, barely runs or quits at so infrequent local drives. Sometimes seems flooding out?..raw gas smell one time. Sometimes seems not getting consistent fuel or the signal to run the efi correctly. I've run the fuel pressure gauge on it since day one, and will put a more accurate one on this week, because it seems "stuck on 20-ish"when I battled it today.

I am ex vw dealer mechanic from those days..so I sure have some idea of how they work....but I am at the point of looking for my spare 67 T3 carbs and linkage today.

It sure seems to be happening at/during the transition from cold engine to fully "up to full temp" only. The last two times, 2 months apart, broke down temporarily at the same spot, same 4 or 5 miles away from home. Then, if I can find a spot to get off the road, and if I can restart it or fight the heck out of it to keep it barely running...after a while of that fighting, it clears right up.

I was given the VW dealer EFI "test console" by a samba friend, but have no instructions, and my question is...will that testing box even pick up a very random fail, if it is then running fine during testing??

Yes, I've swapped brains. not sure which brain part numbers of the 3 used ones I have is in it, (without looking right now). When I swap to another brain, I am then forced to adjust the pressure sensor adjustments & idle screw to get it to run decent...which has me baffled.


Today it broke again, but after sitting awhile, I got it to barely keep running, then fought it very hard for 5+ minutes of crapping out, then it went to perfect instantly (with no adjustments as I don't have no tools in the car).

I cannot trust it any longer.. I hate to lose the efi, but...

[Mike Fisher]

Did you try to adjust your fuel pressure with the fuel pressure regulator on the right hand side of the engine? Check to make sure your metal fuel return line is not getting plugged up. I don't think you really need a better gauge as mine is a 0-100 water pressure gauge from Home Depot that does the job for me. Don't give up on the EFT yet as they will run good!
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https://imgur.com/user/FisherSquareback/posts
69 FI/AT square Daily Driver
66 sunroof,67,70,71,71,71AT,72,72AT,73 Parts
two 57 oval ragtops sold
'68 Karmann Ghia sold

Society is like stew. If you don't keep it stirred up you end up with a lot of scum on the top! - Russ_Wolfe/Edward Abbey

[dailydrivervw]

[KTPhil]

Random intermittents are almost always due to faulty wiring connectors, which loosen their grip over time and with temperature changes (even though the plastic connector housing may seem tight). I'd spend an afternoon carefully extracting the push-on terminals from the plastic housings, cleaning and gently tightening them, then re-insert. I bet that fixes your issues. If it doesn't, then we may suspect other components like faulty head temp sensor, pressure regulator, but almost never the ECU.

The VW/Bosch test consoles will not pick up these loose connectors. They really are just a timesaver compared to what you can do with a VOM.

Swapping ECUs shouldn't require an MPS adjustment, unless it was the wrong unit.

How are you adjusting the MPS? Being experienced with these cars, you do know that the "plug" (diameter of a dime on the end of the MPS) is not a plug at all, but the full-load enrichment adjustment?

Does the MPS check out for vacuum leaks and also electrically first?

I would inventory part numbers for at least the ECU, MPS, and TVS, to make sure you have a matched set.

[Bobnotch]

Also, check your voltage when it's acting up. I found with my old 71 Notch that it would start loosing voltage the longer it ran. I set up an 8 mile loop, and at mile 5 I would be down 1.7 volts from where I started. This causes the engine to run rich. At the end of my loop (back in my driveway), I would be down to 12.2 volts from my 14.4 starting voltage, and would have a rough, missing running engine. Changed the Voltage Regulator, and everything was good to go again.

Before I found the VR going bad, I ran a bunch of other tests, to eliminate possible problems like a pump going bad, or the CHT needing ballast, injectors leaking, or the fuel system bleeding down, or things like that.

I had also ran a long piece of fuel hose to check my running fuel pressure. It stayed the same pressure on my loop, so I could take that off the list of possible problems. I'd also tested all of the sensors too, and they checked out within spec, so it wasn't 1 of them causing the problem.

Sometimes you just have to go over everything, just to find the 1 thing that's causing the problem. In my case, the VR was the last thing I tested, which turned out to be my problem.
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Bob 65 Notch S with Sunroof
71 Notch ...aka Krunchy; build pics here;
http://www.thesamba.com/vw/forum/viewtopic.php?t=249390 -been busy working
64 T-34 Ghia...aka Wolfie, under construction... http://www.thesamba.com/vw/forum/viewtopic.php?t=412120

[KTPhil]

[dailydrivervw]

[raygreenwood]

To collect what all the other excellent answers already stated....into one pile.

So.....you put a more accurate fuel pressure gsuge on jt....and the pressure is CORRECT?
Be advised....."20-ish" wont work. It needs ti be EXACTLY 28 psi. Once you find out if it needs slightly more....which some do in hot climates.....you csn add a MAXIMUM of 3 psi (31 psi max) ....and ONLY if you have an ACCURATE gauge.

For now leave it at 28-29 psi.

So.....it starts and drives....ok.....but at the same 4-5 miles away from home.

That means that its starting out rich enough...and is either getting richer as you drive:

Causes of that:
Voltage dropping
CHT or TS-2 not reducing resistance as it heats up or starting out too high in the first place
Vacuum leaks opening up from heat or vibration
System grounds and connections getting loose from heat or vibration.

Or......
Cold start injector leaking along with....
Injectors leaking somewhat as well
CHT / TS-2 getting disconnected through heat or vibration
TS-1 reading incorrect.
The auxiliary air regulator not closing which can signal about 1/4 open throttle at the MPS. Usually to cause flooding/stalling...this is coupled with a few other items from above.

Or your system is adjusted grossly too rich in the first place at the MPS and it slowly loads up with unburned fuel. This is actually more common than you think.....because the injector timing fires two of injectors against closed valves and one at a partially open valve and one at a fully open valve. But....this usually only happens if you are idling for aong period. Above about 1800 rpm.....its not a big issue.

Ray

[Hip2besquare]

I had similar issue and it was my head temp sensor. It ran fine when cold but as it heated up it ran exactly like yours. Replaced it and all was good.

Richie