Yank needs some help on mk2 cold bogging

[Messer262]

Hello all. I’m wishful that the UK folks are more helpful on the forums than the US central people.
Almost finished sorting my 88 mk2 16v.
The issue I have is that at cold startup if I drive off soon after it bogs and has no power until it warms up. Once it hits 80 degrees C it kicks in like a mule. (It could be around 85 degrees or so as gauge doesn’t show as minute degrees) once it hits about 80 degrees it has full power but before that no matter what it has none.
I feel it is something with the Kjet but am not familiar with them. Aside from this issue the car is amazingly sorted and once warm runs like a dream.
Your help and/guidance would be most appreciated.


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[Messer262]

Maybe a little more detailed info if it helps:
1988 scirocco 16v kjet
Cold start and idle seem fine.
When driving cold at low rpm it appears normal. So driving slow through my neighborhood in 1st gear seems ok. A low rpm shift to 2nd is ok. When I pull out onto roadway and trying to run to run up rpm and gain speed it just refuses. It seems like it cuts back and bogs down. I can hardly get it high enough rpm to shift to 2nd going up a moderate incline (load). Then when in 2nd it doesn’t want to rev and give power. Now it I drive it until it warms up I can watch the temp get up and right around 80C it’s like a switch is flipped and then it will just open up and rolls right through the rpm.


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[whiteshark]

Temperature Sensor for Cold Start system
Looks like:
https://www.ebay.co.uk/itm/Vw-Golf-Mk1- ... Sw-ntfXhko

New ones are compatible that are made for the De Lorean or getting one second hand in the states on the Vortex should be easy enough.

Or else your 5th injector is playing up.

Is it warm where you live or does your car start easily on a very cold day. If its very cold, with either of these two not working the car would be very difficult to start. If you live in a warm area most likely the Temperature sensor.

Can you hear your ISV switch on and make the noise when you turn the key to the first stage before actually starting your engine?

Based on my own experiences and even working with my mechanic, all trial and error, starting first with the fifth injector.

At least your car starts and eventually warms up for some fun!!!!

[Messer262]

Thank you for the reply. As for local temps, it is pretty warm here. Today is a bit cooler (70F) but warmer all summer with same issue.
I’m not sure what ISV is but I do hear the fuel pump and some buzz from under the hood switch on. I’m not familiar with the 5th injector so I’ll work out sourcing and ordering the cold start switch you mentioned and see if that resolves it. Thank you for some guidance on this.


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[chopperoli]

Sounds more like a duff warm up regulator. Get a fuel pressure tester

[Messer262]

Can you expand on the warm up regulator theory?


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[chopperoli]

Well you said it runs sweet once it's warm?
Tons of info out there, here's a starter for 10
https://www.tasteslikepetrol.net/2020/02/bosch-k-jetronic-basics/

[Messer262]

I’m having trouble locating that part on my 88 16v. Do you have any guidance as to where it would be located. I’ve looked at what the part looks like and traced the fuel lines and don’t see anything that looks like it. Would it be underneath the car?


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[Messer262]

Ok. I think I have solved it. My car doesn’t have the typical WUR that most have. It has a control pressure regulator.


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[Messer262]

Found this little bugger and am working on a replacement. Are these something that is adjustable or should be monkied with if suspected to be the issue? It looks like the screw on the face there is adjustable.



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[chopperoli]

I wouldn't mess with that unless you know what you're doing?
I can't recommend this book strongly enough: Bosch Fuel Injection and Engine Management, by Charles Probst
ISBN 0837603005

[Messer262]

Thank you for the response and guidance once again. I did put a replacement “fifth injector” cold start regulator in it and it didn’t seem to help anything so that certainly doesn’t seem to be it. I have some parts incoming including a couple of warm up regulators for the side of Medusa so I have been told that could be the source as well so why not replace everything.


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[chopperoli]

Imagine replacing everything but not knowing why. For me, the CIS pressure test kit is mandatory