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My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

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Hi there

I'm having some issues regarding to hot start vs cold start and idle when warm / cold.

Maybe first a bit of history of my car 😉 (sorry for the long read …)

It's a 83 1.8 DX GTI, which has been tuned mildly 21 years ago.

I had driven it about 5000km's and then put the car away for restoring… What didn't started for about 3 years ago…

About a year ago I disassembled the engine to inspect whether it didn’t suffered too hard standing still during that +20 years. Disassembled everything except the pistons and the valves in the head. All looked ok, so reassembled it all with new gaskets and stuff.

I have about 500km’s on it now, the engine runs smooth and likes to rev, no issues when pushing it high and low. 😉

Now the engine has been tuned as I said, I had it completely rebuild and in adidtion threw in some extra goodies. Unfortunately the builder stopped he's business 12years ago, so no assistance from that side.
Anyway, it has a another camshaft, the head has been blueprinted/portmatched, the flywheel has been lightened and the compression is raised. I think the bottom is balanced too but i'm not 100% sure…
That's it, no special exhaust (I now, it would definitely benefit from that, but Rome wasn't built in a day :-)). Other than that everything is stock.

Now for the problem(s):

Usually when the engine is cold, it starts from the first tick, no need to throttle before or during starting. However he then idles too low and drops dead.

I can raise the idle to a good level for cold start, (but not as to what the manuals say 900rpm, I need to raise it to just above 1000rpm to run smooth). But when I do this, the engine idles too high when hot, it then goes to about 1300rpm.

When the engine has been running for a bit (does not need to be really hot) it usually takes for about 3 to 5 sec’s to start. So no drama, but not what it should be.

Also the idle is not always supersmooth, it can go up and down for about 50 or 100rmp’s.

The problem is that I know that the tuning partially could be responsible for how it behaves now. But I dont know until what point. Should I be able to get it tuned better, or is this normal behavior you guys think?

Maybe there are some things I could check / do, to make it start more smooth and get the idling more on point?

I know there are a few starting points to start looking for solutions.
For example I already tested with some break cleaner whether there are no leaks in the inlet zone after the throttle body, but the engine did not respond to that. Most hoses are new or in very good condition.

I tried to squeeze the AAV tube when the engine is running cold and it clearly responds to that and drops in rpm or even stops running.

I also renewed the fuel accumulator and fuel pump, fuel lines are partially renewed and in good condition, no leaks or fuel smell. The ignition has been setup by a local garagist.

I was thinking about the AAV, what if it opens good for cold start, but does not close sufficiently for the hot idle? Could this be the reason why it idles to high when hot?

Although, you have to adjust the idle on an hot engine, so that should mean that the AAV isn’t opened up enough when cold? How can you decently inspect the AAV?

I know there are several other items to check, for example the WUR and CSV.

I am going to a friends garage on saterday and will set my CO to what is prescribed by Hanes and will then experiment with the ignition timing. After that I wanted to adjust the idle.

Some other advice or better starting points? As you can see I have a few questions and would love some guidance of you pro's out there!

Thanks,

I believe you asked Mars Red LA2A?
Mars Red it is !

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What fuel are you using, super unleaded or normal?

You can get a lumpy tick over when you fit a performance cam shaft.

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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Sounds very much like mine used to be, I have a high life cam and cold tickover used to require careful balancing of the throttle and the first couple of miles until warmed up,was a bit interesting to say the least.

I found my co2 reading was 0.50 , a friend with the aid of an old Gunsons tuner set it at 1.8, adjusted the timing a little and it fixed the problem - it's still lumpy on idle, but that's the characteristic of the cam. also runs much better and starts from warm better when 4unning on Tesco Momentum 99RON as opposed to Jet 97 superunleaded..

Golf GTI Campaign 1983 Mars Red, Ford S-Max 2015, Audi TT 180 quattro 2003, Fiat 500C 2013, Golf GTE MK7.5

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RichardHall said

Sounds very much like mine used to be, I have a high life cam and cold tickover used to require careful balancing of the throttle and the first couple of miles until warmed up,was a bit interesting to say the least.

:lol: :lol: indeed it is a bit interesting, but good practice for the heel-and-toe technique, not allowing it to drop when breaking ;) :lol:

So where I live (Belgium) the highest octane you can get is 98 (as far as I know), so its unleaded 98 fuel i'm getting.

Now last weekend a friend of mine told me that the petrol wasn't as good in just any station, and that I should throw in a lead replacement additive. So that's what I did, but didn't really had the chance to drive it thoroughly for the petrol to be mixed. Hope this helps too.

Interesting to note that it run's best at CO˛1.8, I will take that into account tomorrow.

I will start with the CO˛ and ignition and from there on gradually see what gives best results.

I hope my friend has an pressure reader for the injection so I can test / adjust the WUR.
Just need to find a way to check the AAV thoroughly.

Thanks for the advice guys !



I believe you asked Mars Red LA2A?
Mars Red it is !

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NO……. don't use a lead additive, it's a waste of time and money, all water cooled VWs from 1974 have hardened valves and valve seats so they don't need lead in petrol to lubricant the valves as that is what lead additive does… It's only old British cars that need lead in petrol….

You should be fine with 98 RON petrol as that's what VW recommended when they made the car and even with the mods you should be ok with it.

If you make sure the timing is stop on and the spark plugs, HT leads, dissy cap, rotor arm are all new or in good condition get the car nice and warm so the fan kicks in the wait for the fan to stop then adjust the mixture (CO) to 2%, you may need to adjust the idle speed as well, I find my car runs better at 1000rpm as less things seem to rattle at that idle speed, mixture adjustment is last thing you touch when tuning the car.  :thumbs:

Last edit: by mark1gls


1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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Hi all!

So, in the meantime …
I went to my friend on saterday and played a bit with the ignition, idle and mixture.

The CO was this high, (above 7%), that bringing it down to a reasonable mixture was not really an option.
So we focused on the ignition and the idle rpm.
Once this was set I did a few test runs.

The engine is now really better in the low rev range, it picks up faster and feels like more torque in the low range.

It also has a much flatter curve now. Before this setup it really started to go from 3500-4000rpm. Now there is no real peak that I can feel.

Downside is that I have the impression that before it was faster in the high rev's, but that could just be an impression. I have unfortunately nothing to compare or measure it.

We then tried again to fiddle with the mixture, but no go, going under 4% is no option. To be honest I don't even know where its at now…  :$
So my friend suggested to throw in an injector cleaner, just to be on the safe side. I have to empty the tank before I could notice any difference (will be this coming weekend though, trip to Ardennes is planned  ;) ) but not too much hope on that.

The idle has been set much higher, at about 1.100rpm. what has been confirmed to me by different people to be normal for this type modified engine. So now there is no idle issue when starting it cold.

mark1gls thx for the extra input!
As I read your feedback I came to realize that indeed the builder back in the day said that the engine should not have issues with unleaded fuel, so when the bottle is finished I should soon notice a difference if there is one.

The ignition items you mention are all new, so they should be good.

Only things that I did not changed where the fuel lines to the cilinders and the injectors. But they where renewed when the engine was rebuild 20y ago (and so aprox between 5.000 and 10.000Km's ago)

At this instance, unless people have some real straightforward issues I could check or do I think the only real option now is to put it on the dyno, with somebody that has real old skool knowledge.
This is the only way to fintune the engine at its best peak performance.
But I know I want to buy a new exhaust with a new header downpipe. So I need to wait on this before putting it on the dyno.

Oh just this thing, I have been observing the balance of the engine (I dont know whether the bottom of the engine was balanced or not when modifying).
If it wasn't done by the engine builder at the time, then VW did a good job, it rev's nicely to +6000rpm without extra vibration or so.
So, happy with that :thumbs:

I believe you asked Mars Red LA2A?
Mars Red it is !

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If the CO was that high either someone with heavy hands has messed with it or possibly the warm up regulator is faulty or has lost it's power supply.
A pressure gauge is invaluable and will save you money in the lonmg run, so many change this and that when they get faults in the vain hope it will solve their problem when with a gauge you can pin point where the trouble is.

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Re:

cedar said

If the CO was that high either someone with heavy hands has messed with it or possibly the warm up regulator is faulty or has lost it's power supply.
A pressure gauge is invaluable and will save you money in the lonmg run, so many change this and that when they get faults in the vain hope it will solve their problem when with a gauge you can pin point where the trouble is.
Hi cedar , I'm looking for one currently and will check for sure. Keep you posted!
The reason the CO was this far off was because I took the injection apart for cleaning when rebuilding the car, and upon reassembling just turned in the screw without any measurement…

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Hi all!

Just had the chance to test a few things.
At first, I think my thermo time switch is broken. After +10sec's cranking the engine it was stil giving power to the 5th injector. I says it should stop after 8sec's.
But, when the engine was warm at 122°F I retested and it was not giving power any more.

Then I started to test the injection pressure.
One thing was remarkable however, the pressure goes up very fast, and does not decent until after the engine is powered off.

Below you can find the measured results together with what I think I should be expecting. I recalculated the temp and pressure to °F and PSI, so maybe the rounding is a bit off but generally I should be close I think.
Oh yes, this is a Belgian car, I think there are other values sometimes with UK or US cars?

I hope that somebody has quick insights on what is wrong, is the WUR not working right? Other suggestions?

PressTest.PNG

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HI Mr Cash

Your system pressure looks okay but your cold control pressure I think is way too high, I had all the info for the 1.8 written down but can't find it now.

According to Haynes the cold pressure should be about 1.5 bar whiuch is for a 1.6 but the 1.8 shouldn't be that far away, I'm no expert but using simple logic  your problem could be the WUR or a partially blocked return fuel line. I seem to remember there is a gauze filter in one of the connections to the WUR, have a look at that.
 

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My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

Hi Cedar, as a rebuild/dismantling of the WUR doesn't seem to be easy and certainly not cheap, i want to start with testing the return line.

But i cannot seem to find in my haynes how it's done…

Any ideas anybody?

Can i for example just put my compressor on it and blow from the engine to the tank?
Of course all being very carefully … Opening the tank, and not putting stress on the line with 10bar or so… Just blowing softly from a distance and listening at the tank whetter you hear it bubbling in the tank?

Also, what's the impact on the Thermo valve not operating properly? I have to retest again maybe, to see when it really did,  but currently it seems to not stop after 10+ sec's (should be 8sec).

Cold start is no issue currently as it is warm enough here i guess (+/-20c°)…

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My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

Just re-tested the Thermo valve operation. I kept it cranking until +20sec's, and 5 injector kept receiving current… So it is definitely broke…   

Another thing i noticed was that it only got about 10.5 volt, isn't that low? Battery is charged by a trickle charger and it is reading 13.2 volts currently. So no issue there…

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My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

Luckily it's not always about troubles did a small drive with my son yesterday and shot this picture

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I believe you asked Mars Red LA2A?
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Hi there

I'm not one for spending money if I can avoid it and my attitude is that these engines were designed to start in the middle of a Berlin winter so if it's 20 deg C where you are I
would just disconnect  the fifth injector.

' I've never had to check a fuel line so I can't help there but would think it wouldn't do any harm to blow some air through, that's what I would do. Also I've never had any trouble with WUR's so can't help there either but there must be someone here who has had one in pieces.

Once you get one of these running how it should it will go on for ever with a bit of maintenance, let us know how you get on.

 

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My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

Hi all, sorry I left this thread unanswered. Apparently the starting issues disappeared magically, so maybe a clogged line that freed up eventually? It now starts and runs smoother then ever.

Just another quick question about my engine though.

To make it decently run I have to put the CO way high.

If I go to the Belgian MOT it might fail (at first it wasn't necessary for older cars to be measured, but they are changing regulations ) and with this CO it would surely fail.
And, … it makes it stink… Haha sometimes if I'm stuck in traffic for a long time, it makes me sick when I drive windows open

As the engine is altered, I first always thought it was normal that it is like that.
But the more i read and learn about it. I start thinking it isn't normal.

Can anybody explain why the CO should be put that high on my engine?
Could there be a part that is malfunctioning or wrongly setup that is causing this?

All advice is welcome!

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What is the CO reading currently on the car and what is the pass for your MOT?

UK MOT is 3.5% and about 2% is what you want for a standard GTi.

1988 Mk1 Golf GTi Cabriolet 1.8cc DX, K-jet. Daily drive. 317,000 miles and counting
1978 Mk1 Scirocco GLS 1.6cc FR, Webber carb. Weekend toy.

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My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

Last reading was over several months ago, it think it read over 4… If I remember well it was 4.7

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Re:

mark1gls said

What is the CO reading currently on the car and what is the pass for your MOT?

UK MOT is 3.5% and about 2% is what you want for a standard GTi.
Last reading was over several months ago, it think it read over 4… If I remember well it was 4.7

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Re: My mildly tuned DX 1.8 GTI isn't running all that smooth, guidance needed !!

MrCash said

Hi all, sorry I left this thread unanswered. Apparently the starting issues disappeared magically, so maybe a clogged line that freed up eventually? It now starts and runs smoother then ever.

Just another quick question about my engine though.

To make it decently run I have to put the CO way high.

If I go to the Belgian MOT it might fail (at first it wasn't necessary for older cars to be measured, but they are changing regulations ) and with this CO it would surely fail.
And, … it makes it stink… Haha sometimes if I'm stuck in traffic for a long time, it makes me sick when I drive windows open

As the engine is altered, I first always thought it was normal that it is like that.
But the more i read and learn about it. I start thinking it isn't normal.

Can anybody explain why the CO should be put that high on my engine?
Could there be a part that is malfunctioning or wrongly setup that is causing this?

All advice is welcome!

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Anybody any sensible advice?

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Hi - In your table you have a reading of 5bar on the gauge after 3.5 minutes with the tap open, that's too high, that's system pressure.
What you should be getting is the hot control pressure reading which I had written down but now cannot find, for the 1.6 according to Haynes it's about 3.5 so the 1.8 won't be a long way from that.
Check the WUR for a blockage.
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