"Trailer-hitching" bucking problem, Rapid detrioration from running perfectly Options

[boxster914]

Hi everyone

My perfectly running 71 914 1.7 D-jet has deteriorated rapidly this past week.

Early in the week I noticed what felt like a power drop out during a drive. It was very slight and only happened once and I wasn't sure I didn't cause it by unconciously lifting off the gas.

The next drive it happened a few times and was more pronounced. It was then that I knew this wasn't an imagined problem.

On the third drive it was like a bucking bronco, surging and stopping and the engine cut out a few times. It was undriveable.

Today it will start but won't run. The engine cuts out when I try to rev it and the red light comes on.

I've done some searching here but haven't been able to draw any conclusions or come up with an actionable strategy to diagnose the problem. I'm seeing people trace it to spark plug wires, air fuel ratios and bad distributors.

Is there a step-by-step process that you can recommend for me to get to the cause of this? (I'm a newb so I probably will need help with abbreviations like AFR, TPS, etc.)

Here is a video of it's rough idle yesterday when it was still running.

https://youtu.be/n61CP6O8UgM

[wonkipop]

thanks for putting up that video.

its hunting as its trying to idle.
i'd go looking carefully over fuel first.
check the filter.
check the fuel pressure if you have a guage and can do it easily.

i've got a similar thing mine does when it gets warmer here.
and its sounds just like that.
i think in part is due to having a rhd car. took me a long time to work out what it was.
without going into detail too much what happens is my fuel overheats due to the very small volume of fuel in the circuit (the bulb at bottom of tank is way smaller in a rhd car).
combined with a new fuel pump in original position it can cause bubbling in the lines etc and fuel starvation. fill the tank up to halfway and its gone just like that. only in hot weather. but its exactly that kind of hunting.
so i would go there first. not saying your problem is that, but not getting adequate fuel through will do something very similar.

an air leak in a L jet will also give you that but tends to go up and down in revs a bit more than that. not really in the know about d jets and air leaks etc.

but that sure sounds like fuel issue from your vid.

it could be that its got clogged injectors, but the only way to know for sure is to pull them and get them tested. maybe leave that until a bit further along.

good luck with it.

stay methodical.

all other suggestions above are correct.
just go through everything one thing at a time.

[Lockwodo]

thanks for putting up that video.

its hunting as its trying to idle.
i'd go looking carefully over fuel first.
check the filter.
check the fuel pressure if you have a guage and can do it easily.

i've got a similar thing mine does when it gets warmer here.
and its sounds just like that.
i think in part is due to having a rhd car. took me a long time to work out what it was.
without going into detail too much what happens is my fuel overheats due to the very small volume of fuel in the circuit (the bulb at bottom of tank is way smaller in a rhd car).
combined with a new fuel pump in original position it can cause bubbling in the lines etc and fuel starvation. fill the tank up to halfway and its gone just like that. only in hot weather. but its exactly that kind of hunting.
so i would go there first. not saying your problem is that, but not getting adequate fuel through will do something very similar.

an air leak in a L jet will also give you that but tends to go up and down in revs a bit more than that. not really in the know about d jets and air leaks etc.

but that sure sounds like fuel issue from your vid.

it could be that its got clogged injectors, but the only way to know for sure is to pull them and get them tested. maybe leave that until a bit further along.

good luck with it.

stay methodical.

all other suggestions above are correct.
just go through everything one thing at a time.

Hi wonkipop. My '74 2.0 with FI is having the same symptoms boxster914 and you have described. You're reminding me that I've observed very small bubbles in my fuel line. Here's what happened: I replaced the fuel filter which of course drained the line to the engine, so I wanted to purge the fuel line of trapped air. I separated the fuel line at the cold start valve and attached a clear tygon line which I put it into a clear jar, then bumped the fuel pump (by turning ignition on and off). I could see bubbles traveling through the tygon tubing, which I expected. Thing is, I repeatedly turned the fuel pump on and off and I continued to get very fine bubbles in the line.

I'm in California where the ambient temp is around 75. The car has a 2 port fuel pump installed below the fuel tank. The missing happens when the car is warming up so I don't think this is a fuel heating up issue. I'm wondering if I have some sort of leak in the fuel line, something that's letting air in but no fuel out as far as I can tell?

By the way, the tank is near full and I verified fuel pressure is correct and does not fluctuate when the missing occurs.