Sputtering when cold.

I have an annoying issue which I can’t seem to trace.

When the engine is cold pushing the throttle down makes it splutter, to the extent that it’s undrivable for the first 5mins. Once it’s warmed up, It’s fine.

If I slowly increase the revs it’s fine, but if I do it quickly it’ll splutter and die. (See video) it starts from cold first attempt and idles fine. Just won’t rev. I have changed coil, leads, plugs, rotor arm and dizzy cap. New fuel pump.

Anyone point me in the right direction to what to look at next?


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Golf cold start issue - YouTube


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What is the WUR pressure? It is the choke equivalent in kjet.
It should be around 1.5bar when cold and rise to around 3.4bar when warm from a combination of engine heat and warming the bimetallic strip inside it.
Sounds like the engine is not getting enough fuel when cold, the WUR controls this.
Another possibility is a vacuum air leak that seals off when warmed up, ie the metering flap is not seeing all the metered air due to an air leak and therefore does not move the metering pin far enough to give the engine enough fuel.

Okay, I had a litttle google and it seems there’s two types, 16v and 8v. Mine has no vacuum pipe to it. Is that correct?

Second point about vacuum is something I’ve suspected myself.
When I purchased the car the plug that goes to vacuum take off to the dizzy the wires were cut and not going anywhere. I reconnected them to matching colour wires which seemed in a logical place. Could this be the cause?

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Hi,

Thanks for the insights. Checking the Warm-Up Regulator (WUR) pressure is a good idea. If it's not reaching the specified values, that could indeed explain the cold-start issues. Also, your point about a potential vacuum air leak affecting metered air and fuel delivery makes sense. Investigating these aspects should help pinpoint the problem. Good luck with the troubleshooting! you should learn about
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Best,
Marcia

BarnyE said

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That is just the device that feeds the MFA and controls the mpg indicator.
Spray carb cleaner around the bay and listen for the revs to increase as an indication of a vacuum leak.

All said and done though, you cannot troubleshoot kjet without a pressure gauge. Well you can just start replacing parts and get lucky, but it gets expensive very quickly

There's a gauze behind one of the banjo bolts on the WUR. It's usually that blocked which causes the control pressure to be too high. I would always check that first. 

[mention]Yomp [/mention] thanks!!

Good news! (Semi good news)
On yomps advice, took the banjos off and sure enough one of the gauzes was a bit gunked up. Bit of white spirit, tooth brush and cotton bud got it all cleaned out.

Now it revs from cold. A slight hesitation, a cough but then it revs. It used to cough then die.

I made a bit of wire from the positive on the 5th injector straight to the battery. If I connect it to the battery it splutters when idling, but then revs with no coughing at all.

So it confirms it’s just not getting enough fuel to rev when cold.

So next question. As the gauze was gunked up, is it worth taking the WUR apart to check that out. I had a quick look at the fuel filter, it seemed pretty clean. Is there something else I should take apart and clean?

Thanks in advance,
Barny


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If you don't know when the fuel filter was last changed fit a new one, it's best to replace them every couple of years as any girt or dirt will play havoc with the fuel system.
Bit of info and check which size fuel filter you have as there is 2 sizes, shout if your having trouble finding one and I’ll post up a link.

View topic: Gti fuel filter - The Mk1 Golf Owners Club


You can buy a service kit for the WUR, it can be tricky to get the bolts out as they have a slotted head, I had to use a impact screw driver to undo mine.

https://www.ebay.co.uk/itm/292038768448?hash=item43feddf740:g:olkAAOSw7hRWO1nH&amdata=enc%3AAQAIAAAA4E1dL5uBVuK%2FCNmgIIqh1CnmrvQ1Q%2FBaD%2B1NaapXfx3A1rqKem8FuQaWMLFZeDQMhBWodmBwBSLcIr2%2Fg7D6jj3hbVKOW1rOuuRru%2BCOzfokzwKix8OnxJIY9CkUjpW8UfAxp1ZTrDAJqZfTqE2BxYqib5YGrnZo974%2B4jYvbAsiYljg3TjxOszuuyoPhfn8zvSd4IeAQv13W20ksOY6B4%2FIa0S7FWq6%2BXzZ8%2FOdA4ZWVwkqj0bma42CppLrmR3zgpYYTLpjrXqPkbUxeZ3JDc2YueA69Yoo3hFypR4HhttC%7Ctkp%3ABk9SR5DauaeCYw

BarnyE said

[mention]Yomp [/mention] thanks!!

Good news! (Semi good news)
On yomps advice, took the banjos off and sure enough one of the gauzes was a bit gunked up. Bit of white spirit, tooth brush and cotton bud got it all cleaned out.

Now it revs from cold. A slight hesitation, a cough but then it revs. It used to cough then die.

I made a bit of wire from the positive on the 5th injector straight to the battery. If I connect it to the battery it splutters when idling, but then revs with no coughing at all.

So it confirms it’s just not getting enough fuel to rev when cold.

So next question. As the gauze was gunked up, is it worth taking the WUR apart to check that out. I had a quick look at the fuel filter, it seemed pretty clean. Is there something else I should take apart and clean?

Thanks in advance,
Barny


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Inside the WUR is a steel shim diaphram behind 4 screws and is Sealed by an o ring. Ive had success by flipping the diaphram and replacing the o ring for new. I do have a fuel pressure guage so can see pressures and I have seen a differance after doing this little job. I think the new o ring helps the diaphram gain some movement again.

fyi O ring spec

Viton M1.5 x 14mm ID 17MM OD

So the searching continues for the cause of the spluttering when trying to rev from cold. I’ve changed the fuel filter, rebuilt the WUR.
Today I looked into the air flow sensor thingy. It was a bit gunky so brake cleaner’d it down so it’s clean, how freely should it operate? Is there a way to take it apart to clean inside?

Thanks again.


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