Help and Advice Please - Misfire

[BIG_MVS]

OK Guys just got home after picking up my new GTA Turbo, broke down on the way home

Firstly it's not been used as an everyday car for the last 3 years(although the previous owner did take it for the occasional spin and checked fluid levels to keep it ship shape), and get it MOT'd.

The car is running a bit lumpy on load but I put that down to the lack of use and the need for a good service.

After getting onto the motorway the car started to misfire(judder then lose power) after 10 secs or so the car would then resume and all is well. After doing this every 10 mins or so i was then doing the old "just please get me home!!"We then hit traffic and the car misfired again but then did not restart. I pulled over then waited a while and it then fired up - off we went again. After more traffic the problem occured again.

Eventually got home, checked all the spark plugs and they seem fine, dizzy cap looks fairly new as well.

Any ideas or is this another preverbial GTA "can of worms"???

Martin

Maybe start by checking all the earth straps and your plug leads. I had a misfire on mine once that new plug leads cured. I'm sure someone can offer you some much more technical advise. Being a GTA it could no doubt be any of a hundred possible causes!

A severe missfire while driving will be fuel. The 6 pot GTAs can drop to 5 four cylinders and still feel smooth if a plug or lead is out. Change dizzy or rotor anyway...

Sounds like dodgy fuel pump or wiring. Only other thing ive had this symptom with too is low battery voltage when the alternators knackered.

Btw, which car did you buy?

The best way to check HT lead integrity, is to run engine and open bonnet at night. If the leads are shot you will see black pool illuminations.
I.e. sparks tracking down them.
Also from a previous post look up lack of spark.
This to could be your TDS sensor on flywheel.

[Alpineandy]

Not the cause, but it may contribute:
If it's done so little milage at low revs recently, bung some fuel system cleaner through the tank.
It's amazing how much a system can get gummed up with little useage.

Could be the fuel pressure regulator on its way out. If it's been sitting around for a long time the diaphragm may have started to corrode and perforate. (Mine popped thanks to the local petrol station getting water in their underground tanks after the floods back in 2000)

If it is you can get the symptoms you mention as the car overfuels and the injectors are given more petrol than they need which then can't be burnt efficiently. You end up getting massive flat spots that feel very similar to an electrical fault.

Its a pain to diagnose but check the exhaust as it can splutter when revved and you'll see soot being chucked out. Basically it'll be out of tune and far too rich.

Also try driving at night with the lights on. If it's an earthing fault / alternator etc then dimming lights should give you a clue.

[BIG_MVS]

Cheers guys for all the replies, will try them one by one, got an Xr25 coming round to my house tomorrow hopefully so it may be able to pick up a problem there.

DaveG - It was an ebay special that was on a couple of weeks ago, 1988 "E" plate in Red.

Anyone else had similar problems please let me know.

I will hopefully get it fixed before Donnington!!

I sympathise with you, i've had the same feeling for two months since i bought my GTA. Like you it broke down on the way home from purchasing it, turns out the headgaskets are shot.

Try the basics first, replace or clean all contacts (dizzy cap, leads, plugs and add some redex, clean or remove the air filter etc). It does however sound to me like it could be more to do with the battery terminals/connections or earth strap for the car to be juddering so much and to happen so instantaneously.

[BIG_MVS]

Right Update.

Now got the car running alot better after an oil and filter change. Also put all the boost vacuum pipes back where they should be and what a difference Goes like a quick 21 Turbo now

Still got the above problem tho

Swapped the coolant temp sensor as that was coming up with a fault on a Xr25 diag. Checked all the HT leads at night in pitch black, no sparks although the neighbours think I'm weird!

The C/O reading was 0/-0.1!! So it was running far too lean, we have changed this to run at around 1.7%, runs a lot smoother.

On the way home I had a minor splutter but it seemed to run ok, problem solved I thought. I then filled up with fuel and put some redex in(as was advised) not 3 mins down the road and it misfired, can having a full tank of fuel cause this???

Anyway my fuel pump is very noisy when hot(ok when cold) so I'm hoping that changing that and a new fuel filter will sort it. The fuel pump seems to struggle it's that noisy!

Any more ideas let me know.

Anyway my fuel pump is very noisy when hot(ok when cold) so I'm hoping that changing that and a new fuel filter will sort it.

Actually, you've jogged my memory! Sorry I never mentioned this before but it was a while ago and I'd forgotten about it. I remember changing the fuel filter on mine once and this also seemed to fix a misfire I had. A garage did it for me at the time and I can't remember whether they changed both the main filter and the pre-filter or just the main filter. Anyway, possibly something else to try.

Just to complicate matters when the fuel pressure regulator was perforated and overfueling my car (causing the misfires) the fuel pump became very noisy.

The noise was much louder than normal and a different pitch. Fuel regulator changed it went back to normal volume and sound, obviously the extra pressure in the system was straining the pump at idle enough to hear the difference.

The fuel regulator is a doddle to change if you can find a spare one!

[BIG_MVS]

Hi Darren,

Whereabouts is it in the engine bay mate?

Also was your car fine when cold and the fuel pump OK when cold?

Mine only seems to have this problem when it's hot, the fuel pump gets noisey when it's warm too, it must be related???

Cheers,

Martin

Hi Martin,

I really wouldn't like to bet money either way on what the cause is - its a GTA after all!

However yes it was more of an issue when hot - on cold the car needs more fuel anyway and the ECU settings etc allow for this. Hence a bit of extra juice isn't as much of an issue. When hot the settings are at their idealised levels so the extra fuel causes massive flatspots.

I can't remember if the fuel pump was quieter when cold to be honest but the problem wasn't constant anyway and that's why it was so difficult to diagnose. The fuel pump did sound like it was 'wheezing' and struggling though.

The fuel pressure regulator is under the 'V6' plenum near the water pump it's the small metal doodah with all the fuel pipes entering it. On later models two were fitted, one acting as a pressure damper.

Fuel filters are meant to be replaced at the major services so if they're old they should be changed anyway - the pair are pretty expensive by the way.
Fuel pressure regulator is about £60 standard I seem to remember or you could fit an uprated one for a bit more. Check the other threads for the cost of the pumps as there was mention elsewhere.

The fuel pump will get noisy if the reg is knackered because the pressure in the lines will be around 4-5bar.

Easy way to see if the regulator is knackered is pull off the vacuum feed off the top of the regulator. This will give atmospheric pressure to the diagphragm and simulate a full load situation. If it makes no difference then the reg is stuck/perforated. On a perfect running car, doing this would cause the car to chug and bog down a bit.

Truthfully though, even with loads of extra fuel, it wont cause the car to cut out, this is normally only from running lean. Ive run a car with massive oversize injectors and no feed to the reg, and its idled and drove fine, just a little unresponsive..

Might be worth checking the front pump and filter. If the front feeder pump isnt supplying enough to the rear pump, then it will make noise (as if running out of fuel) and can misfire/cutout.

Check the wiring to the pump, as it gets warm it may be pulling more current.

[BIG_MVS]

OK driven the car a few times since(too busy at the moment ) and there has been no misfire - Darren I owe you a beer!

Changed the fuel pressure reg for an FSE valve which I modified as I was going to use it on my 21T. I think I need to get the pressure set correctly on it but it seems to have resolved the problem(fingers x'd)

The fuel pump still gets noisy after the car warms up so will still change this.

Next job is to fit the shiny induction kit I purchased from Dave G....