TheSamba.com :: View topic - '78 Super Beetle FI; Rough idle, no acceleration

Wed Aug 30, 2017 4:21 pm

Hello everyone, I am new to The Samba and hope to find some help for my car. I recently bought a 1978 Super Beetle convertible with fuel injection. The car has about 98k miles on it, and has engine troubles.

When purchased, the car did not start, but previously ran. The previous owner said he could not get the car over 10mph, even when at full throttle.

TL;DR We are not mechanics, and need some help. The car starts quickly, but idles terribly (slow, shakes, sounds rough). Any use of the accelerator causes the engine to stop. During idle, directly spraying gasoline into the air intake boot (AFM removed) causes the engine to increase speed, and idle smoother. We believe the engine is somehow starving for fuel, or has incorrect combustion 'ingredients,' improper amounts of fuel and air (poor stoichiometry). Whether this is cause to mechanical or electrical problems is not confirmed.
- We are referencing the Bentley VW Service Manual
- Starter replaced
- New battery
- Spark plugs replaced (0.028in gap)
- Fuel filter replaced
- Fuel pump tested, ~38psi
- Double relay replaced, no difference
- ECU tests (continuity and Ohms) appear normal
- We have discussed converting to a carburetor, but we want to condemn the fuel injection first, due to cost and labor of the conversion.
- The work done previously on the car does not seem perfect, it appears that shortcuts were taken and incorrect methods used (not that we are perfect VW techs by any means); ex. wires were cut and spliced without wire nuts, and using duct tape to cover them. This is also seen in the method of hot-wiring the fuel pump directly from the fuse panel.

The story:
We installed a new starter, and the car started and idled. Upon our first drive, we could not exceed 10mph (as previous owner indicated). After that first drive, we removed and investigated the AFM/MAF. The bottom cover was off, many teeth on the black gear were broken, and it seemed rough overall. We cleaned the internals of the AFM (strictly avoiding the electrical contacts) with throttle body cleaner. We have not yet condemned the AFM, because replacing it seems near impossible (lack of replacement parts). After this, possibly just coincidentally, the car ran worse.

The car would start, idle slow and rough, shake, and sounded terrible overall. However, removing the plug to the AFM would make the engine idle faster, smoother, and sounded better.

The car then refused to start. We began troubleshooting, starting with the double relay and ECU. We purchased a new double relay, installed it, but there were no differences. Continuity and Ohm testing proved the ECU was good, so we moved on to fuel. We discovered the fuel pump hot lead was being powered by a hot-wire, ran directly from the fuse panel to the pump (which made the fuel pump operate during 'ignition on,' as opposed to 'ignition crank'). We removed this wire, and replaced the original hot wire, returning the fuel pump to optimal operating times.

Next was fuel pump testing, which initially refused to work. A few encouraging taps of the fuel pump brought it back to life, although it seemed to pump out debris (into a catch basin). Because of this, we replaced the fuel filter, and measured the pump output (~38psi). Output was also tested from fuel lines in the engine bay, with the same reading. Because of this, the fuel pump seems to be working within normal limits.

Now the car started again, but still idled terribly, as before. We removed the AFM, started the car, and sprayed gasoline into the air intake boot. The engine revved higher and smoother following this, which made us suspect that the engine is somehow starving for fuel (i.e. inadequate delivery, too much air/improper stoichiometry, etc.). After a while, the car refused to start... again.

We then removed the spark plugs, which seemed loose, and were caked black. Replacing the spark plugs (gap 0.28in) allowed the engine to start, but once again, idle terribly.

Currently, unplugging the AFM makes no difference with idle. Touching the accelerator makes the engine die. Spraying gasoline into the air intake boot makes the engine rev higher and smoother. We are working down the fuel injection troubleshooting list, but we are not mechanics and need help. What should be our next plan of action?

Wed Aug 30, 2017 4:32 pm

THE mass air flow sensor looks to be burnt.. can you move the arm over and take another picture.. ? you see the silver stuff where the rest is all black? that area is what I am interested in seeing..

Wed Aug 30, 2017 4:35 pm

Wed Aug 30, 2017 5:05 pm

vwjetboat wrote:

Wed Aug 30, 2017 5:12 pm

that is the issue.. that tells the computer how much fuel to add.. with those spots worn away it can not give the computer right info.. Is get another.. but get others to chime in also.. to make sure

Wed Aug 30, 2017 5:24 pm

vwjetboat wrote: that is the issue.. that tells the computer how much fuel to add.. with those spots worn away it can not give the computer right info.. Is get another.. but get others to chime in also.. to make sure

Thanks for the help! We always figured that it needs to be replaced, but finding another one, even re-manufactured, has proven difficult and expensive.

Wed Aug 30, 2017 5:29 pm

Narch22 wrote: vwjetboat wrote: that is the issue.. that tells the computer how much fuel to add.. with those spots worn away it can not give the computer right info.. Is get another.. but get others to chime in also.. to make sure

Thanks for the help! We always figured that it needs to be replaced, but finding another one, even re-manufactured, has proven difficult and expensive.
and this is why people spend about 250 -300 for a carb conversion... sad to say but its the truth.. ive converted over a dozen in my lifetime.. years ago.. because of this reason ..

Wed Aug 30, 2017 5:30 pm

Worn tracks in the AFM can definitely cause a mid range stumble, you can loosen the screws holding the board down and move it so the wiper is on some fresh contact area. But those AFM's are calibrated by Bosch with a laser (insert Dr. Evil meme here), pushing the board around changes the entire dynamic of the sensor and is really just a temporary "limp home" fix, but it may get you on the road until you can find a better one.

You mentioned a stuck pump and some crap coming out, have you sent the injectors to your local Bosch authorized diesel service center?, or Witch hunter or Cruzin performance for a cleaning and test? How about a flow test?, just because it makes the correct pressure can it maintain it after a few liters have gone through the system?

You'll also want to replace all the rubber hoses as well as the injector to manifold seals, they look old and dry, L-jet can't take the slightest little vacuum leak.

As for swapping to a carb don't, if it runs now you are 1/2 way there, since you say you aren't that mechanically inclined the FI is a better choice since it requires no special tools or meters and no "trained ear" to set up, if you can read the troubleshooting manual and a pressure gauge or Volt/ohm meter you are qualified to fix it. Once it's done it's ready for another 40 years of neglect before it acts up again.

Wed Aug 30, 2017 5:32 pm

busdaddy wrote: Worn tracks in the AFM can definitely cause a mid range stumble, you can loosen the screws holding the board down and move it so the wiper is on some fresh contact area. But those AFM's are calibrated by Bosch with a laser (insert Dr. Evil meme here), pushing the board around changes the entire dynamic of the sensor and is really just a temporary "limp home" fix, but it may get you on the road until you can find a better one.

You mentioned a stuck pump and some crap coming out, have you sent the injectors to your local Bosch authorized diesel service center?, or Witch hunter or Cruzin performance for a cleaning and test? How about a flow test?, just because it makes the correct pressure can it maintain it after a few liters have gone through the system?

You'll also want to replace all the rubber hoses as well as the injector to manifold seals, they look old and dry, L-jet can't take the slightest little vacuum leak.

As for swapping to a carb don't, if it runs now you are 1/2 way there, since you say you aren't that mechanically inclined the FI is a better choice since it requires no special tools or meters and no "trained ear" to set up, if you can read the troubleshooting manual and a pressure gauge or Volt/ohm meter you are qualified to fix it. Once it's done it's ready for another 40 years of neglect before it acts up again.

^^^ ditto.. good advice.. i hate seeing a FI converted..

Wed Aug 30, 2017 5:46 pm

DO NOT GIVE UP ON THE FI. On this forum you have access to the most knowledge available. I also have a 1978 Super and have started from scratch and gotten it thru smog and running and reliable now.

Listen to Busdaddy. He knows these systems. One thing I can tell you is that these engines will not tolerate ANY vacuum leaks. I am talking micro ones. Spray around the engine with it running with carb cleaner and listen for any change in RPM.

Check your fuel pressure, make sure the pump and regulator are functioning correctly.
Keep posting here and let the forum help you. You will love it once you get it dialed in and turn the key and go.

Good luck!

Wed Aug 30, 2017 6:12 pm

busdaddy wrote: Worn tracks in the AFM can definitely cause a mid range stumble, you can loosen the screws holding the board down and move it so the wiper is on some fresh contact area. But those AFM's are calibrated by Bosch with a laser (insert Dr. Evil meme here), pushing the board around changes the entire dynamic of the sensor and is really just a temporary "limp home" fix, but it may get you on the road until you can find a better one.

You mentioned a stuck pump and some crap coming out, have you sent the injectors to your local Bosch authorized diesel service center?, or Witch hunter or Cruzin performance for a cleaning and test? How about a flow test?, just because it makes the correct pressure can it maintain it after a few liters have gone through the system?

You'll also want to replace all the rubber hoses as well as the injector to manifold seals, they look old and dry, L-jet can't take the slightest little vacuum leak.

As for swapping to a carb don't, if it runs now you are 1/2 way there, since you say you aren't that mechanically inclined the FI is a better choice since it requires no special tools or meters and no "trained ear" to set up, if you can read the troubleshooting manual and a pressure gauge or Volt/ohm meter you are qualified to fix it. Once it's done it's ready for another 40 years of neglect before it acts up again.

Thanks for the response. We have not yet inspected the injectors beyond continuity from the cables, however flow and function of the injectors is one of the things we want to test next. And I can say with 99% certainty (without even testing) that there are MANY vacuum leaks... we have one line laying on the ground, which was simply dangling from the car when we bought it. At first our mindset was: how bad could some vacuum leaks be? But after reading your post, as well as some others, we are taking it more seriously. So our next steps will be testing the injectors and getting new vacuum lines, and sorting that out.

Wed Aug 30, 2017 6:18 pm

KKiley wrote: DO NOT GIVE UP ON THE FI. On this forum you have access to the most knowledge available. I also have a 1978 Super and have started from scratch and gotten it thru smog and running and reliable now.

Listen to Busdaddy. He knows these systems. One thing I can tell you is that these engines will not tolerate ANY vacuum leaks. I am talking micro ones. Spray around the engine with it running with carb cleaner and listen for any change in RPM.

Check your fuel pressure, make sure the pump and regulator are functioning correctly.
Keep posting here and let the forum help you. You will love it once you get it dialed in and turn the key and go.

Good luck!

I don't want to give up on the FI because it deserves to be fixed, but we have just met so many dead ends. I will definitely keep posting here to help on our journey.

Wed Aug 30, 2017 6:18 pm

I uploaded a YouTube video of the symptoms at idle: https://www.youtube.com/watch?v=SlIafkt3WNs

Wed Aug 30, 2017 6:26 pm

You'll learn that the FI engines are a "love/hate" relationship. I've learned a ton from the FI gurus on here and how to deal with my 78 FI. Be patient and do the simple things first. Make sure the ignition is in proper working order. When it's idling spray the carb cleaner at different spots and listen for an RPM change. There are only 4 gaskets on this engine: 1 at each intake where they meet the head, 1 under the throttle body, and 1 in the plenum(pictured).

Vacuum leaks might also occur at the injector O Rings, S Boot, or any of the vacuum hoses. Getting the injectors cleaned is also a good thing.

Wed Aug 30, 2017 6:48 pm

You need to start at the basics and then, one step at a time. Focus.

Adjust the valves to .006 cold, then run the engine the best you can for a few minutes. Carb cleaner if needed. Then do a compression check. Lets see what condition the engine is in, so we can tell if it is worth looking further.

If compression is good, we will check spark, fuel pressure and more importantly volume. We will check the volume from the injectors next and spark quality.

Re,ember, basics first. Followed by one system at a time.

Wed Aug 30, 2017 10:29 pm

That nut right there was my nemesis.
Came out once, ended up in the head, bouncing around in the intake valve area. 2nd time, I used blue loctite on the nut, then the whole stud worked it's way out and ended up in the head again.
Now, the stud is red loctited in and the nut is a lock nut. It will not come out again, lol

Thu Aug 31, 2017 5:36 am

Agreed that FI is the way to go. Be patient before converting to carb. You will find AFM it will take some time.

Fri Sep 01, 2017 11:37 am

Try this 1st, it's simple and will give you and idea of what is happening.
Unplug the temp sensor2. It can be found on the drivers side head, with a single wire coming off from it. That will put the system into the default mode of full rich. That should give you enough fuel to have a decent idle and be able to rev it up.

Take carb cleaner and hit the intake manifolds and gaskets, and the various vacuum lines. See if you get any rpm response from the spray.

You know the engine is running lean. You just need to go thru each system one at a time and eliminate them.
Good luck!

Fri Sep 01, 2017 3:40 pm

Maybe try the "glue" used on defroster strips?

https://www.walmart.com/ip/Permatex-21351-Rear-Win...mp;veh=sem