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95 Golf 2.0 hot starting/running problems

First post in years - hoping for insight.

My 2.0 litre GTI Mk. III is becoming increasingly troublesome when starting from a hot engine in hot weather (which is rather common in Texas, unfortunately)

First symptom was intermittant and began maybe two summers ago. On very hot days if I'd parked the car (fully warmed up) for about 10-30 minutes (heat soak is really getting going), the engine would start fine and run for a few seconds happily... then the first time I pushed the clutch in and came to a stop, the RPMs would fall like stone to zero. Dead. I could restart, but it wouldn't idle without help from the accelerator pedal, so driving was a 3-footed (or heel-toe) affair. This might go on for 30 seconds or 3 minutes, after which it recovered its composure and ran just fine. Even when it refused to idle it had good power and revved OK.

If the car sits long enough that it cools down, then the problem isn't there.

I assumed this was idle control valve and cleaned it. The problem usually disappeared for awhile when I did this. It was a summer problem, infrequent, and I pressed on.

Last summer the problem was more frequent, but no worse.

This year it reappeared with a vengeance, and a new symptom developed about a month ago.

Hot day driving at 65 mph or so on the highway. I went to overtake a large truck and as I did (70-72mph?) I lost power. It felt like fuel starvation. Putting the accelerator down further made the engine feel like it had hit a rev-limiter (it hadn't). Backing off the pedal, the power returned as normal. This happened about 3 times in succession (over 10 seconds?) and then vanished. It pulled fine. I overtook.

This week the power-loss symptom appeared twice - once at highway speed and once pulling out of a parking lot. It's always under load. That's why it seems like fuel starvation to me.

Today it started and ran fine hot, but trying to pull out of the parking space produced no forward motion. The engine would not rev or pull above 1000 rpm (but it didn't die like it has in the past). I stumbled out of the parking space and into the lane and spluttered along for about 50 yards. Then suddenly it was back, good as new. Revved fine. Rand fine. Pulled fine. We came home.

I sat down to ask for opinions.

The only thing I can ad is that today the fuel tank is low (in the red) but not completely empty by any stretch.

Thoughts I'm entertaining are fuel pressure regulator, fuel pump (ouch), vacuum in the fuel tank, computer problem (ouch), or a bad sensor that I can't think of.

Oxygen sensor seems unlikely, but I have a spare so it may go in.

Idle control seems ruled out for now.

Injectors would have to all fail at once for this sort of power loss, seems unlikely.

It may be two seperate problems.

Thoughts welcome,

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Fuel line restriction? Maybe the filter? Doesn't explain the hot only condition tho'.

Mark '95 Jetta GLS

Reply to
Mark Randol

While at a safe spot, home or friend's house, try testing the ign. coil and spark plug cables by spraying them with water. This is best done at night so you can see any sparks jumping around. At a safe spot in case the vehicle dies out and does not start up quickly again.

I am thinking a weak spark. :-)

Have you performed any "tune-ups" lately? New spark plugs and wires, cap, rotor, fuel filter, air filter, etc.? I would say start with the basics first to rule them out. ;-) Any DTCs? Or has the engine check light ever come on?

JMHO

Reply to
One out of many daves

Thanks to you both.

Did plugs and wires about 10k miles ago while I had the manifold off for my 120k timing belt change. Figured I'd better do it while it was easy. I could check the spark, but it runs so well when it sorts itself out (usually 30 seconds to 2 minutes of rough running/dying) that I can't believe the ignition can be it... and it's one of those modern coils without fluid. Do they ever fail, really?

Fuel restiction, again, I'd say yes but it's so intermittant and so predictable WRT temperature and warm engine... that I can't belive it's the fuel pump or the fuel filter (since neither one should really notice the engine temp or the underhood temp, which is what I think is the trigger.

No engine lights, and the '95 is pre-OBD-II, so I can't do it with the code reader I have here anyway. Grrrr. Specialist tools.

-charlie

Reply to
Charlie

In article , snipped-for-privacy@host.com says... and it's one of those modern

Yep. Had two of 'em go bad on a GM product, and the VR6 coil packs would crack and let water in.

If the fuel pump is going, it could be heating up while it's running and once it's shut down, having problems getting going again. Hey, it makes more sense than my suggestion of a fuel filter.

I feel your pain there...

Straws to grasp at...

Here's a possibly unrelated question. How's your oil level? Does it go UP? I'm wondering if you have a sticky/leaky injector. After shutting it down while warm, the fuel rail despressuring into the cylinder would make it run like trash for a couple minutes. Letting it sit to 'cool' would let the fuel either evaporate or seep past the rings. Don't remember your other problems tho', so can't guess whether it'd do anything.

Way to check would be to look at the plugs. If they're wet, or if you crank the motor with the plugs out (disconnect that coil primary first?) and gas spurts out the plug holes...

Since you're not saying it's also an alarm problem, I won't mention the hood expanding from heat and opening the hood alarm switch, disabling the engine ;)

So is the check engine light on at all? Bulb's good, that is it comes on when you turn on the car?

Mark '95 Jetta GLS

Reply to
Mark Randol

Interesting thought. I'm certainly going to try to rig a fuel pressure gauge this week so that when it does its trick I can pop the hood and watch the needle... not sure I have a gauge that goes high enough right now.

Oil level actually falls a bit at this age, and the oil doesn't smell gassy. The bad running is really a powerless sort of thing without any apparent smoke (which I'd expect from a serious over-fueling problem).

I could certainly check the plugs without too much trauma.

Disabled the alarm awhile back... because it was the devil's own plaything. Horrid bugger - went off whenever it pleased. It's been banished.

That's a fair question. I don't actually take stock of that when I go to start, honestly.

Thanks for the thoughts. Fuel pressure is first. If I can get the gauge on the rail I can use that to test for pressure when sitting too.

-charlie

Reply to
Charlie

I've never done this, but I suspect a FI specific, and probably a VW specific adapter are required?

It never hurts the check and read the plugs. Sometimes it's a really good diagnostic tool

Main cause of alarm problems is the rear door harnesses at the hinge. Second I'd guess is the wire going to the trunk lock. After that are the front harnesses and the hood switch.

I don't usually either, but it's worth a look

My rule of thumb is to check the easy and cheap stuff first, then go on from there ;)

Another thought. An even easier & quicker way to eliminate the ignition is to hook up a clamp on timing light. If there's a misfire in the wire it's clipped to, the light will 'skip' and not flash steady. Go through and to this for each wire. I found a fouled plug that had shorted out this way on a different car. While it's hooked to #1, you can check the timing too and see if that's doing something strange. Never done it on this car, so I'm not sure where the scale would be, if there is one!

Mark '95 Jetta GLS

Reply to
Mark Randol

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I have replaced TOOO many of these ign transformers/coils that have failed or were weak. The weak ones caused the engines to become hard to start. ;-) DON'T JUST CHAnGE IT GUESSING THOUGH!!!! You should be able to test the spark output by watching the color of the spark. When you start the engine when it is still hot then the engine might be under a very lean condition which should be demanding on the spark. The fuel injected inside of the engine could be absorbed by any deposits on the valves. Maybe pulling a spark plug out and looking at it and down into the cylinder might give you more info. Maybe some mist coming out of the cylinder(s) might indicate fuel injectors leaking. Of course if the fuel pressure does not drop when the engine off, injector leakage is doubtful. :-)

Yes you should test the fuel pressure during different stages of running or non-running. Tests should be in the Bentley. The fuel return line will take fuel that is heated by the engine compartment and route it back to the fuel tank. So there is a possibility that the fuel pump could get warmed by this fuel. I would doubt that this is the problem in your case but the pressure test should determine if it is. :-(

There will be someone close to you with the vag-com tool. ;-) Oh and I have had many running problems that were corrected by staying away from mid-grade gas. Which grade and brand gas are you using?

Reply to
One out of many Daves

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