Engine stutter under heavy load

Hi all your expertise please!
1. Car idles absolutely fine at 1000rpm
2. Revs freely when not in gear.
3. Drives perfect when accelerating at say 75% of max.
4. But if I ‘floor it’ it stutters when being pushed. Happens in 2nd, 3rd mostly.
I don’t drive it that often so took it for a good blast today and strangely it was fine initially but toward the end of my half hour drive it then played up.
The fuel in the tank is fresh.
Thoughts?


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Is it injection or carb?

Sorry 1.6 gti


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Few things I have found on my 1.6gti over the years.

Fuel pump getting blocked. - mine did as described change the fuel pump and fixed it but it then blocked up again, then I did the fuel tank. Fixed that part now.

Dizzy - the little hall sensor electrical connection is a bit dodgy on mine and under full life it can make it lose connection and loss of spark. Ranging cuts out and the recovers - need to order a new Dizzy but other issues to fix first.  

Fuel lines - long metal ones on the drivers side can get pin holes in them. I am in the process of replacing my return line with copper.

Vacuum advance - check it by sucking on the vac advance pipe.If you cannot suck any air it’s ok. If you can suck and blows through it then it needs replacing.

Timing in general. Make sure you have your timing set correct this can seem perfectly fine and lower power ads but as you go through the range then can cause issues.

Good luck.


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Thanks for those ideas [mention]Backinblack [/mention]
I’ve had the car a year but a lot was done to it before I got it…

Fuel pump: always sounds noisy to me but heard they’re like that..? Mine looks fairly new. All braided lines too.
Fuel tank is also new looking and has copper lines so hopefully all good. Filler neck has been replaced.

Will check the timing advance as suggested.

General Timing: it has a TSR engine and used to tickover at 1100 ish rpm. I thought that was a bit fast so pulled it back to 1000. But wonder if it should be 1100 if the engine was tuned and needs that timing level? It’s been bored out to 1680cc, Mahle pistons, vernier cam, larger valves/springs, piper cam etc. So could be a non standard timing set up?


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With all the mods I would get it somewhere that can tune it correctly for you unless you really know your stuff.

As for noisy pump. My brand new one lasted about 500 miles until is clogged up again. If it’s particularly noisy worth dropping it off and looking inside the one end for bits of muck.

Assuming you have quite a few horses under the bonnet then also could be simple fuel starvation at higher revs. Maybe the lines and pump size is simply not big enough.

Tuned cars give flat spots and eradicating them costs £££ then a few more ££££.


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Hi, bit of a slow update … but re-advanced the timing back to where it was when i first got it - and seems much better. I now only get a slight hesitation when ive got my foot 90%/flat out.

Ive also found a local reputable old school rolling road tuner who knows mk1’s so am going to book in a couple of hours with him.

Return of the stutter gremlins. Went for a much longer test drive and after a good 45/60 mins with a nicely warmed up engine, the stutter under load returned. Not as bad as before so I think adjusting the timing has helped.
But my fuel pump is very noisy.
Am I right in thinking a ‘81 1600 tintop has no fuel tank pump? Just the main one.
Could it be the swirl pot in the tank?
Am wondering if there’s a supply issue as heard pumps really hum when this happens..?


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Hi knowledgeable people, can anyone help? TIA

Based on previous comments, decided to replace the fuel pump and filter…

1. Question on the pump: Should i go genuine Bosch from Classic VW or SSP from Heritage? Or something else?

2. Also read it can be worth putting an Audi 80 pre-pump translucent filter in to keep an eye out for contamination. Anyone done this? Will a generic in line filter do? Any links?

TIA

Checked easy stuff like fuel filler cap? If it's not venting properly you get a bit of vacuum on the fuel system, starvingthemotor. Spark plugs and plug wires? Plug wires can cause similar issues. You can also bump the fuel pressure at the CIS distribution head to account for the bigger motor. There's a little hole and a hex adjustment but you need some additional tools to do it right. Inline fuel pressure gauge and exhaust gas analyzer…

nedrager said

Checked easy stuff like fuel filler cap? If it's not venting properly you get a bit of vacuum on the fuel system, starvingthemotor. Spark plugs and plug wires? Plug wires can cause similar issues. You can also bump the fuel pressure at the CIS distribution head to account for the bigger motor. There's a little hole and a hex adjustment but you need some additional tools to do it right. Inline fuel pressure gauge and exhaust gas analyzer…

Cheers for the ideas.
1. Hadn't thought of the filler cap. Interesting I sometimes here a 'whoosh' when i undo it. One time some fuel actual spurted out due to the pressure in there! That doesnt seem right, does it? Do i need a new filler cap - a vented one?
2. Have changed the plugs recently but will do the leads too then.
3. I think the CIS should be set up correctly as its a TSR engine so i imagine they did all that when they tuned it up. Hopefully.

gregpank said

nedrager said

Checked easy stuff like fuel filler cap? If it's not venting properly you get a bit of vacuum on the fuel system, starvingthemotor. Spark plugs and plug wires? Plug wires can cause similar issues. You can also bump the fuel pressure at the CIS distribution head to account for the bigger motor. There's a little hole and a hex adjustment but you need some additional tools to do it right. Inline fuel pressure gauge and exhaust gas analyzer…

Cheers for the ideas.
1. Hadn't thought of the filler cap. Interesting I sometimes here a 'whoosh' when i undo it. One time some fuel actual spurted out due to the pressure in there! That doesnt seem right, does it? Do i need a new filler cap - a vented one?…

That doesn't sound right to me, i dont believe it should do that. There's any number of places to get a replacement, I think they're all vented, but not sure. When you have issues pop the filler cap off and see if it makes a difference. Then you'll know for sure. Happy hunting!

nedrager said

gregpank said

nedrager said

Checked easy stuff like fuel filler cap? If it's not venting properly you get a bit of vacuum on the fuel system, starvingthemotor. Spark plugs and plug wires? Plug wires can cause similar issues. You can also bump the fuel pressure at the CIS distribution head to account for the bigger motor. There's a little hole and a hex adjustment but you need some additional tools to do it right. Inline fuel pressure gauge and exhaust gas analyzer…

Cheers for the ideas.
1. Hadn't thought of the filler cap. Interesting I sometimes here a 'whoosh' when i undo it. One time some fuel actual spurted out due to the pressure in there! That doesnt seem right, does it? Do i need a new filler cap - a vented one?…

That doesn't sound right to me, i dont believe it should do that. There's any number of places to get a replacement, I think they're all vented, but not sure. When you have issues pop the filler cap off and see if it makes a difference. Then you'll know for sure. Happy hunting!

Interestingly Heritage list both "Vented" and "Non-vented".
https://www.heritagepartscentre.com/uk/volkswagen/golf-mk1/fuel-induction/fuel-tanks-fuel-fillers.html

I have the Non Vented so will try switching over to Vented and see if that helps…

Fuel injected car should have a non vented filler cap as you need some pressure in the fuel tank.

The vented filler cap is for carburettor cars.

There's is a breather valve underneath the wheel arch which may be blocked?

It's normal for a "whoosh" of air when removing the filler cap especially if you've gone from a full tank to low but petrol should not be spitting out…

mark1gls said

Fuel injected car should have a non vented filler cap as you need some pressure in the fuel tank.

The vented filler cap is for carburettor cars.

There's is a breather valve underneath the wheel arch which may be blocked?

It's normal for a "whoosh" of air when removing the filler cap especially if you've gone from a full tank to low but petrol should not be spitting out…

Ah thanks for clarifying. I'll have a look at the breather valve. Looking at Haynes it seem i can just unbolt, give it a cleaner, then reattach. Seems simple enough…

Just remembered another detail, maybe it will help: The car takes a few tries to start. When its doing so, i hear lot of gurgling under the car - like its slowly filling the pipes and filter with fuel, or the tank is gurgling… After a few goes the car starts and no gurgling.
Another sign of fuel pump on the way out?
If so, should i go mechanical or electric pump replacement?

Hi chaps, left this a while but determined to get it sorted over the winter... Any further advice on my previous comments? TIA

If you can hear the fuel pump something is amiss.
How Big of a fuel tank do you have, or do you have a space saver spare tire or full size.

As over here GTI's were all tin tops with 10 gallon tanks and full sized spare tires.

Hi yes the latter. Hope that helps


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