Hesitates under acceleration

Golf Mk1 1.8 1987 Cab hesitates when accelerating - other times ok….

Changed spark plugs, air filter, coil so far.  Was thinking it was more electrical.

I have been told that the pump was replaced 2 years ago.  Its a bit noisy due the insulation missing.
Plan to change fuel filter and HT Leads.

Could it be anything to do with the 5th injector?  It sometimes is harder to start, other times it will start on the button.

Why is ok sometimes and others not?  Any suggestions will be much appreciated.

Hesitation on accel is possibly but not limited to:

Duty Cycle out of adjustment (CIS)
Fuel Pressure Drop (possible bad pump as you don't normally hear them running)
Blockage in the tanks swirl pot.
Vacuum leaks

TIMING.

Thanks - will lookup what CIS involves.  I have ordered new pump, fuel filter and leads.
Will also check timing and blockages.  What about the fuel distributor - do they go wrong at all?  Are they serviceable?
 

Dupe post

Fuel distributors don't go wrong exactly, but they can get gummed up and the control plunger can wear/get stuck.
To check it properly you need to measure fuel pressures - and if you can't get it adjusted properly then it might be worth getting it refurbished (£££), or doing it yourself (kits are available - I've just done mine). It's worth taking some time to read up on how CIS works - plenty of Google info. Here is a good starter - Bosch K-Jetronic – Part 1, The Basics – Tastes Like Petrol
the 2nd article on testing is not Golf specific but the principles are all the same.

If you can get a Haynes manual it gives you all the specifications, and takes you through some tests, for example, your fuel should flow 900cc in 30 seconds. Injector volumes should be within 80% of each other, etc, etc. Bentley manual is probably similar but I don't have one of those.

There seems to be a lot of fear of CIS, but as it is a primarily mechanical system, it's not that hard to fault find - you just have to be very methodical and take your time about it as swapping things out randomly can cause other issues.

It is certainly easier to check the timing and making sure all the ignition side is correct before messing with the fueling side, so I would start there and make sure that is 100%.

J

Sadly I don't have any first hand CIS information, but I do read volumes on it….

I am more a Diesel / Digifant guy.

paceman said

Fuel distributors don't go wrong exactly, but they can get gummed up and the control plunger can wear/get stuck.
To check it properly you need to measure fuel pressures - and if you can't get it adjusted properly then it might be worth getting it refurbished (£££), or doing it yourself (kits are available - I've just done mine). It's worth taking some time to read up on how CIS works - plenty of Google info. Here is a good starter - Bosch K-Jetronic – Part 1, The Basics – Tastes Like Petrol
the 2nd article on testing is not Golf specific but the principles are all the same.

If you can get a Haynes manual it gives you all the specifications, and takes you through some tests, for example, your fuel should flow 900cc in 30 seconds. Injector volumes should be within 80% of each other, etc, etc. Bentley manual is probably similar but I don't have one of those.

There seems to be a lot of fear of CIS, but as it is a primarily mechanical system, it's not that hard to fault find - you just have to be very methodical and take your time about it as swapping things out randomly can cause other issues.

It is certainly easier to check the timing and making sure all the ignition side is correct before messing with the fueling side, so I would start there and make sure that is 100%.

J

Thanks - Yes agree with eliminate as much as I can on the ignition side - low hanging fruit .  The previous owner also investigated and we have swapped notes.
I think the big clue is that 30% of the time is goes like it should do - so if it was timing etc - it would be bad all the time.  

Regarding Bentley Manuals - has anyone tried the online soft copies - 1984-1992 Volkswagen Golf & Jetta Workshop Repair Service Manual BEST
Seems like a good buy ??

Before you delve too deeply….check the mixture.

It won't be the 5th injector, that's only involved in starting.

I ran without the 5th injector plugged in for about 2 years as I had old leaking injectors, once the car is started they don't use the 5th injector.

Had an early 8v mk2 that did this. Was the leads. 

paul_c said

Before you delve too deeply….check the mixture.

It won't be the 5th injector, that's only involved in starting.

Apart from getting a lambda sensor and a meter - is there any other way of checking mixture?

I have also changed the leads today - but have not taken it out yet for a run.

What colour were the old spark plugs?

You do really need to get the car hooked up to a CO meter to check the mixture, what was the reading on the last MOT?

Andy_S said

paul_c said

Before you delve too deeply….check the mixture.

It won't be the 5th injector, that's only involved in starting.

Apart from getting a lambda sensor and a meter - is there any other way of checking mixture?

I have also changed the leads today - but have not taken it out yet for a run.

Smell it. That will give a rough guide.

Also, a CO meter will give a rough guide too. But yes, wideband lambda is by far the best way to do it properly.

Its possible to do it by knowing the characteristics/quirks of how the engine runs (revs up, engine speed change when adjusting etc) at lean-misfire limit and rich-misfire limit then sweeping thru the mixture range the car will run at, then setting a centre value, then tweaking a little either way depending on whether you want it rich or lean (or in the middle).

paul_c said

Andy_S said

paul_c said

Before you delve too deeply….check the mixture.

It won't be the 5th injector, that's only involved in starting.

Apart from getting a lambda sensor and a meter - is there any other way of checking mixture?

I have also changed the leads today - but have not taken it out yet for a run.

Smell it. That will give a rough guide.

Also, a CO meter will give a rough guide too. But yes, wideband lambda is by far the best way to do it properly.

Its possible to do it by knowing the characteristics/quirks of how the engine runs (revs up, engine speed change when adjusting etc) at lean-misfire limit and rich-misfire limit then sweeping thru the mixture range the car will run at, then setting a centre value, then tweaking a little either way depending on whether you want it rich or lean (or in the middle).

Thanks - will try the idle and brake pedal test for the mixture to start with.

I took it for a test run with new Bosch leads and it went well. Old ones were very old and hard.  I am now trying to make it hesitate .

I have ordered a NOS dizzy cap as the one on it has a approx 2 mm play when I try and rotate it on the body of the distributor. Looked like a poor quality pattern part.

The updated parts etc are not going to hurt so will get there.
Thanks!

I thought I would try to see what the mixture was like in between the showers on the golf.

Temp was up - and when I stood on the brake pedal - no difference.

Just to make sure I was going to richen it up by turning the mixture screw clockwise a quarter of a turn, just in case it was too lean.

I grabbed my 3mm allen key and pushed it into the hole, as soon as I made contact with the bolt the revs slowed down, assume I must have been pushing the flap down?

The bolt appears very tight and I was unable to move it…  Is it usually very tight?
Thanks!

Yes normal for things to change in the tick over if you push on the mixture screw in the meter head.
It should not be really tight as it's only a thin Allen key to turn the screw, maybe spray a little WD40 down the hole?

Its important to only turn, not push on, the allen key/tool adjusting. When I did it, I let it sit there on its own and twist it. If it fits properly, should be okay to turn. I think sometimes they put a plastic or wax seal down there though?

Yes, I did lean out the mixture half a turn and what a difference it made. Car has woken up.
Idle is rough - sounds like it has a big cam in there and idle fluctuates between 9-1500.  I have managed to purchase a idle stabilizer valve to try.  I will also get the mixture checked.

An update which is good and bad

I drove the car on Saturday - felt good on WOT over 3k but does not feel so smooth below that and with partial throttle.

I had purchased a inline fuel filter and the lifter pump.
Car is a mk1 GTI Cab 1987 1.8.  Pump was puchased from Euro Car Parts - (VDO)   Manufacturer Part Number:   E22-057-013Z, Other Part Number:   441440210.

Once fitted I started the car and left it on tickover for a while - gave it a few revs once warm - all seemed good.  Took it for a quick drive but I could soon tell there was an issue - no real power - seemed like the engine was always trying to catch up.

One back on the drive I let the car cool down and checked the pump again, all seemed good.  Also checked tank. Small bit of rust at the bottom which I fished out with a magnet and also a small rectangle of steel.  All back again - but no different - car does not want a rev - tweek the accelerator and revs build about .5 of a second after.

Put the fuel filter on as well - no different

Is it the wrong pump?   Or an issue with the pump?  Do they go wrong?  What else can it be???

I am going to the injectors - so made up the tool that is recommended to pop them out.

I wanted to try the tool for fit - and as soon as I had placed it on the union of the first injector - it popped out.  Top  "O" ring looked bad - cannot have been sealing very well.  Hope this will have also caused my bad running.  New ones are scheduled to arrive next week - so will be interested to see how much difference they will make with new O rings.