Vitara Shunting/Missing

[eXc]

Didn't have any replies in Auto electrical, thought I'd try here.

Hi All,

My car (Vitara G16b, EFI) started shunting while driving (not at idle) about 8 months ago. It only did it once, then it was fine for a few weeks. It got worse and worse, now does it almost all the time.

It used to only happen once the car is warm and it happens any time now.

It shunts in a range of situations. It has missed at revs between 2500 and 4000 ( I rarely go above 4000). It usually happens if the car starts to 'bog down' say mid way up a hill. However it has happened on the flat, just crusing at 60 in 4th.

It has done it in 2/3/4/5th gears.

if I remove the Coolant Temp Sensor, the problem goes away mostly. It has happened a few times over a 4 hour trip. The problem is it uses an extra 25% fuel leaving it unplugged.

After a new temp sensor it didn't fix it. Figured it must be computer, replaced computer, same issue.

I have a mate that had an oscillioscope, so we have run it over all the inputs and outputs, the only one that put out an error was the output from the computer to the injectors, which has a point where it cuts.

What else could be in play here, for it to not play up 99% if the sensor is unplugged, but it does when it is plugged in?

Things I have done;
- New Coolant Temp Sensor
- 2nd hand computer
- New spark plugs
- New leads
- Cleaned throttle intake
- Cleaned air filter
- Replaced dizzy cap/rotor (not the whole thing)
- New Fuel Filter
- New Fuel Pump

Videos that show what it is doing;

http://www.youtube.com/watch?v=gtSc6I99NcE" onclick="window.open(this.href);return false;

http://www.youtube.com/watch?v=VWchWChOZ6s" onclick="window.open(this.href);return false;

Cheers
Chris

[zook4fun]

your maf sensor, did you clean that or just the butter fly?

also the tps on these some times move and give a random miss

[watty]

It would probably be a good idea to check the the computor for fault codes could save a lot of time and money.

[eXc]

fault codes don't give out any errors.

Yes, I have cleaned the MAF.

Given that it moslty happens only if the Coolant sensor is plugged in, do you still think it is the MAF? If I unplug either the MAF or the TPS, the car still runs. If I unplug both MAF and TPS, it dies (as expected?)

Cheers
Chris

[gqmudder91]

hey mate i use to have a 95 vitara auto that does the same thing it mostly went away for me when i put overdrive in but since then i replaced the heater hose behing the engine cause it was brittle it fixed it and now only does it about 110 kmh my parents brought it so if u fix it completly could u let me know ? cheers

[eXc]

I have unlpugged the temp gauge and it's been working fine. The car has been working for 4 weeks straight now. It appears that it is a short with the temp guage and something else.

[tazmanier]

Excelent write up. Was there evidence of the short? chaffing of harness? In the vid of the silly scope were you reving the engine or was that just a high surging idle?

Cheers.

-Taz

[Green as Grass]

Wow, I'm surprised about that. I never would have guessed about temperature gauge. I have a carby vitara and it plays games at around 100k/h and when I rev it above 4500rpm. I was sure that mine was a fuel pump issue. It's all above my head but I've been told that the mechanical fuel pump actuator was worn and the way to fix it was to get an electric fuel pump.
Go figure !

[eXc]

Excelent write up. Was there evidence of the short? chaffing of harness? In the vid of the silly scope were you reving the engine or was that just a high surging idle?

Cheers.

-Taz

Well, I jiggled it under the inlet manifold and it seems to be fine. I can't see under there and dont want to take the inlet manifold off. I have now got the temp gauge plugged back in, and the car has ran fine for...2 months or so now I think.

So there you go a short in the system, that was overided when the computer went into limp mode, masked the real issue and suggested it was a sensor.

Silly scope - it was at 2500 RPM if I remember correctly - and yes, I revved it up to there and held it there, It would show the issue in the garage (ie. nuetral) at 2500 RPM, every time (although it took almost a year before it got so bad it would happen all the time).