Stuttering/snatching/misfire?

[Guest DocBurble]

Perhaps you guys (and gals) can help me sort out a problem with my 1.9 Gti.

 

For a while the engine has been snatching back violently while driving along especially when on the last 1/4 of the fuel tank. I've searched the forum but no-one seems to have had the exact same symptoms.

 

So far I have: -

 

Replaced and gapped the plugs

Replaced the dizzy cap & rotor arm

Swapped the fuel pump

Replaced the tachymetric relay

Checked continuity in the fuel pump connector block supply and earth wires

Cleaned all the debris from the bottom of the fuel tank

Replaced the SAD

Checked the Co2

Checked the TPS set up

Replaced the fuel filter

Checked the voltage to the fuel pump both sides of the block

 

The strange thing is the stuttering is momentary, the engine doesn't die it just snatches several times in a row but will still tick over happily and I can usually still carry on accelerating despite the stutter.

 

What should I check next?

 

DocBurble

[Rob_the_Sparky 9]

If it is doing it under hard acceleration then I'd try coil and igintion amp. The ignition needs max power (voltage actually) to get a spark under max load so mis-fire under max load is usually a sign of a weak coil or ignition amp.

 

Rob

[Pug_101 0]

Someone had a leaking fuel pump which gave your sort of problems. The leak was a split hose inside the fuel pump itself (which sits inside the tank), maybe worth a look.

 

Can't find the thread with a quick search, but it out there

[Guest DocBurble]

If it is doing it under hard acceleration then I'd try coil and igintion amp. The ignition needs max power (voltage actually) to get a spark under max load so mis-fire under max load is usually a sign of a weak coil or ignition amp.

 

Rob

 

The misfire happens under small to medium throttle openings not full throttle and I'm trying to work out why it should mostly happen on the last 1/4 of the tank

 

Someone had a leaking fuel pump which gave your sort of problems. The leak was a split hose inside the fuel pump itself (which sits inside the tank), maybe worth a look.

 

Can't find the thread with a quick search, but it out there

 

Sounds feasable but I've already taken the pump out changed it and tested the replacement.

[Guest DocBurble]

Also I forgot to mention that the rev counter is steady as a rock through all of this.

[Pug_101 0]

Have you checked fuel pressure and vacuum for air leaks?

[Doof 11]

So many of these topics popping up recently with varying misfiring symptoms. Be sure to post back your findings when you fix it because im in the same boat.

[Guest DocBurble]

Have you checked fuel pressure and vacuum for air leaks?

 

You are a winner!

 

I did 'check' the main vacuum pipe from dizzy to throttle body a while ago but due to its buried route from one to the other I didn't remove it to inspect it properly.

 

Yesterday as I removed the end from the throttle body 5-8mm was left behind confirming it was perished and most likely split. A quick replacement and bye bye misfire!

 

All the other little jobs at the top of this thread are well worth doing and have certainly helped smooth out and improve the power delivery but the air leak was the real culprit.

 

Also worth noting for the record was the slighly higher water temp problem I had which with hinesight (sp?) now makes perfect sense.