Need help with intermittent running problem with 1978 fulie

[andrew1978convertible]

Hello- I wanted to tap into the brain trust on this one

I have a 1978 convertible, with stock fuel injection set up. The car recently developed an issue where it will intermittently fail to drive/backfire and/or stall. The car runs great when it runs, but when the intermittent problem comes up it will generally idle fine but sputter when you try to feed it some throttle and move- it will buck, backfire and won't go but generally when you push in the clutch and play with the throttle you can keep it running and get back to idle unless it stalls, in which case it will start up again.

The car was garaged and this issue cropped up. I hardly got it to the mechanic and he did some things (I'll summarize below) and it ran fine but then it acted up again. I took it back a few times, so it was outside the past several weeks- I guess my point is I don't think the issue was caused by being outside and water leaking from the convertible top, which is in decent shape at any rate.

The car has acted up after driving for 10 minutes, and also on the first start of the day- it doesn't seem to be engine temp related. After the 2-3 trips to the mechanic I even was able to drive it without issue for about 65 miles on the highway! Next day after that trip I drove it about 15 minutes to work with no issue, then the issue came up later that day after about 5 mins of driving. I was going to have it towed and then after 5 mins of it being off decided to try to start it and drive again and...it did just fine! Drove it straight to the mechanic then.

Anyway, that is some background. In the trips to the mechanics (two different excellent mechanics- one up north NJ the other in south NJ where the car is now) have included the following services done in the past 2 months while chasing this issue:

* new fuel pump
* new fuel pump relay
* new fuel filter
* new points/condensor
* new coil
* new spark plugs
* one vacume hose unkinked
* Valves were adjusted a year or so ago, but only about 300-400 miles
* Checked barn door on the intake for mechanical movement (which was fine)
* One mechanic checked a lot of wires by wiggling when the car was running fine, and was unable to find any movement that caused the running issue.
* The same mechanic looked at the vacuum lines- while some cracks, nothing that appeared to be critical/that would cause such a thing.

When the car acts up it seemed like it's running rich or lean vs being an ignition issue?

Any thoughts or ideas? Things not done include replacing/checking electronics of the insides of the barn door sensor, the CPU itself or changing the head sensor. The fuel injection wiring is a little older/patched up, but the wiggle test didn't cause any running issue.

The issue is intermittent which makes everything more difficult- I stopped by this morning and took the car around the block by the mechanics and it ran fine.

Is there anything else anyone can think of? We discussed conversion to a stock VW carb, but I think that may be pricey- would obviously be most ideal to find the issue and repair that keeping the stock fuel injection system. And of course, I've now spent a decent chunk of change chasing this down the past couple of months...

Thank you for any advice you guys have!!!

-Andrew

[busdaddy]

A new TS2 (head temp sensor) is cheap, try that first. Next I'd do some driving with a fuel pressure gauge installed on a long enough hose that I could see it in a mirror, what's the fuel pressure doing when it craps out?

Some quality time with sandpaper and/or a wire brush cleaning and resecuring all the system grounds wouldn't hurt either.
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[andrew1978convertible]

In general, does a faulty head sensor typically cause intermittent problems like this? They are relatively cheap and easy to change- just wondering if this is the sort of symptom that shows?

[VW_Jimbo]

Bad condenser, first thing that hit me. Followed by vacuum leaks and grounds.
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Jimbo

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[busdaddy]

Yes, it wouldn't be the first time a condensor has disguised itself as another issue.
The TS2 can sometimes cause bucking while driving at speed, dirty or loose threads where it screws into the head or poor contact at a terminal where it connects to the harness or where the harness plugs into the ECU could cause a sudden intermittant rich condition. You didn't mention if it smoked black when it was misbehaving though.
A 4th possibility is the contacts on the fuel pump switch in the AFM need attention, the results of the fuel pressure tests could steer us in that direction.
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[andrew1978convertible]

I didn’t have black smoke when acting up- it did act up once when I was at the mechanic’s Friday and he seemed to think it was running lean not rich based on the smell/eyes watering while he was by the throttle switch in the engine compartment trying to see if he could jiggle anything to get it to run right.

I’ll mention the things you guys note to him though- I wish it weren’t intermittent! The condenser was just replaced so I don’t think that would be it?

[andrew1978convertible]

Thanks for all the input thus far by the way!

Do the computers themselves act like this or is this more likely the afm, head sensor or a faulty wire/groud at this point I wonder...I know tough to diagnose over the internet but we can try some of the things mentioned here.

[Dwayne1m]

[busdaddy]

I'm a little concerned by statements like "new XXX, XXX, XXX, etc.." and "wiggling wires near the throttle switch", if I didn't know better I'd suspect your mechanic has no idea what he's doing with L-jet and is guessing. It's super simple and easy to diagnose and it's not very often you actually have to replace a component if you understand it and do the tests described in the troubleshooting manual.
Have you ever considered getting your hands dirty and doing some of the work yourself?
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[andrew1978convertible]

Maybe the condenser went bad?

The mechanic is pretty knowledgeable- he was doing a fairly high level check just to start out simply before getting too deep.

As far as me trying to do this myself, unfortunately I work long hours with a long commute and have 3 young kids. Maybe in 7-9 years I’ll have a chance to attempt stuff like this but not in the cards for the foreseeable future

[busdaddy]

OK, but the best mechanic for your VW looks back at you in the mirror every morning, even if you don't dive in fully you can at least know what that shop is talking about and may be able to rescue yourself in the event of a minor roadside issue, just saying.......
Some of that list sounds reasonable, others make me think he's firing the parts cannon at it because those evil wires and mystic boxes are filled with witchcraft. Careful testing and decisive proof the replaced part isn't doing it's job is always good practice, especially since any new or rebuilt replacement parts available today are nowhere near the quality of the OG stuff and may make even more trouble later.
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[andrew1978convertible]

Hello. I had the car shipped to a different VW mechanic because the car wouldn't run/was still stumbling when trying to drive it. I drove it about 1 mile and it acted up, so I had it towed to another shop. When they finally got to the car a few days later, they started the car and noticed a fuel smell and a noisy fuel pump. They wanted to change the fuel hoses first. After doing that the car ran fine for a 5 mile test drive, with no fuel pump noise. I'm almost sure he said they checked the fuel pressure and it was better now with the new hoses vs. when the car first came in...

I have to go pick up the car, but I'm not convinced my issue has been solved. I mentioned that this was an intermittent issue and was concerned about maybe there being rust in the tank per things I have read on here- after we spoke, the mechanic then removed the fuel filter (which was replaced about 1-2 months and 100 miles ago) and blew through some air from the output side towards a paper towel and nothing came out- no rust bits/dirt, and the filter appeard to be fine.

My guess is I'm going to pick up the car and after a few mins the fuel pump will start making noise and/or the car will stumble. Pretty frustrating, but he says it ran fine in their road test (so I think I need to just get the car back). The car is about 70 miles away (it was at my family's beach house when it broke down so is at a mechanic in central/south New Jersey and I live in north NJ).

I'm going to have to retreve the car and bring my AAA card for a potential tow if she can't make it home

Searching around this site, it seems given the work that has been done thus far on the car (by now 4 different mechanics), assuming it acts up again I'm thinking it's perhaps gunk in the fuel tank and/or a vacuume leak. The noisy fuel pump leads me to believe it's crap in the tank, but then again I also read on here that there should be rubber mountings and given that the fuel pump I replaced was first re-connected to the mount it's possble the car just doesn't have the rubber mounting bushings? I'll have to look when I get the car back home. If there's no rubber mounting and that's causing the noise (sounds like a noisy dash vent for HVAC..) it could be the stumbling/stalling is a vacuume leak as when the car acts up I can get the motor going and it stumbles and dies when trying to put under some load.

My question is if the pump does start to make noise like it has been intermittently and it's not caused by the lack of the rubber mounting bushings and not caused by a clogged fuel filter, is there a screen or something in the tank that gets clogged with sediment in the fuel tanks for injected cars? Because the fuel pump is a new bosch part, and if it's not the lack of bushings I can't imagine what else would caust that noise other than fuel starvation fron the tank (again, assuming this is my issue vs vacuume leak). It's possible (a) the old fuel pump was fine but they reconnected it to the car without rubber bushings (the first time I brought the car in they noticed the fuel pump wasn't mounted at all or was hanging there somehow) and (b) then when we tried changing the fuel pump for a new one, the new one was also mounted without the rubber bushings...

Very frustrating, especially becasue I don't have much time to deal with this this time of year .

[390nellie]

I had those identical symptoms with my 79 FI a year ago. Replaced gas tank with new one. It has run fine ever since.

[busdaddy]

[VW_Jimbo]

Why not go down and get the car. Go for a drive around that town. If everything seems fine, take off for home. If it starts acting up, leave it for them to fix.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[andrew1978convertible]

I wonder if there is something in the tank itself that gets clogged- a screen or something? I saw where the older carb cars I think have a screen in the tank just not sure of the FI cars?

VW-Jimbo- I was thinking of that- but every time I have gotten work done it then acted up a little later- in one case I drove it 70 miles down to the beach area with no problem but the next day it acted up- brought it to the mechanic by that town and he did the timing, condenser etc and it acted up about 5 miles later. I had it flat bedded to the current mechanic since he seemed to know a little more about the FI bugs- he did the fuel lines, but it just seems like that wouldn't cause the mysterious occasional fuel pump buzzing. I know they took it for a 5 mile test drive after the fuel lines, but it hasn't always acted up right away since this issue has cropped up.

The shop it is at is almost 80 miles from my house- so if I get 10 miles or 15 and it acts up I may as well tow it back up north... I left a message for the mechanic where it is now- when he calls back I wanted to ask him about his thoughts if they they can clean and re-seal the gas tank- if it's something they can do and how costly that would be. Or get a new tank like 390nellie did (but keep the old German tank if the new one doesn't last long per other posts on this site about the quality of the new tanks...)

On one hand I can just give it a shot as is, but on the other I don't feel like the problem was finally solved with the fuel lines and this could eat up half a day (if I go down there, break down and need a tow).

I've been chasing this issue since around May- it's frustrating since I missed the whole summer with the car, and it's been adding up in $$ costs.

[andrew1978convertible]

[andrew1978convertible]

I just got in touch with the mechanic. For my piece of mind, I'm going to have him pull the tank and they can look in there to check it out. I just don't feel right going there to get the car (when they are closed) and trying to drive it 80 miles...and breaking down for the same issue that has plagued the car since May/June.

He said the one fuel line they had replaced was potentially leaking enough that the fuel pressure was being affected by it, but that fuel pump noise is just strange to me- the same noise from the 8-9 year old bosch pump that was in there was coming from the brand new one- it just seems like fuel starvation to me. And even if there was a pressure leak downstream from the pump, why would the pump make that noise- unless it is missing the rubber bushings? I'll have to ask him next week when the get the car back into the shop if they see the rubber bushings on the fuel pump..

Thanks everyone for your input and please keep any suggestions/thoughts coming.

[vwoldbug]

If you can drive it again then after you run it a while take the gas cap off listen for a vacuum noise from the filler neck . Maybe it has a pinched or plugged vent hose . Also has anyone checked and cleaned the grounds for the fuel system . The repair manual should show the ground locations .

[KKiley]