Friday, October 26, 2012

Cold start problem and vehicle shudder around 2500 to 3500 rpms

The Problem is that vehicle is difficult starting in cold.

More details about the problem:---

Without load
  •  It has a pause effect.
  •  Enginedoesn't immediately rise through the rpms
  • Feels  like its lagging. just a tad though. 
With Load 
In gear driving.

  • It misses.
  • It bucks. 
  • when  gas pedal is left off  it clams a bit, but with past 3500, when gas pedal is pressed or it really bucks. 


As per the issue it seems the problem with fuel system.

Try these:---

With the engine running,  put your hand over the muffler tips and see how much force is coming out?
Or other way you can try is,

disconnect the exhaust right off the exhaust manifold (before the cat/mufflers) and compare behavior to see if we have an obstruction in the exhaust.

These procedure will  eliminate the muffler and catalytic converters from the equation.
It's going to be loud as can be, but it should be pretty clear if the shudder is gone within a minute or two.
So to confirm these problem,Pull that exhaust off as close to the engine/manifold as possible...


the exhaust seems to be moving freely. And there is pressure coming out of the exhaust tip and seem to be the right amount.And it has force behind it.
Then the issue is related fueling and fuel system,that has to be checked, inspected.

Get the fuel pressure tested
Also get the timing mark checked.
It can be checked with Mitsubishi scan tool,for Mitsubishi vehicles.

Please note:---
Getting an exact timing setting result is not possible, but if the light is showing between 5 and 20 degrees on the scale you would be "ok". If you see for example off the scale, to what you would figure is 30-40 degrees at idle, then this would indicate an issue.
Getting an exact figure is pretty much impossible on these without finding an original Mitsubishi scan tool for 1985-1993 models.

If timing checked ok,or its not completely off scale,then the problem is not related to timing setting.

In that case fuel system issue is there.

As I mentioned before, fueling issue of one sort or another.

Something is preventing the air from getting from the intake to the exhaust.
The other other thing can be timing belt off from its actual setting,or damaged a valve just slightly, then was corrected without fixing the valve. An unlikely scenario given the vehicle gets a little better as it warms up and is otherwise inconsistent.
Looking at the ignition, we could see a very poorly timed engine causing difficulty pumping through the engine as it would kick back against the crank.

As far as obstructions go, we have removed the exhaust to make sure there are clogs there. The intake is easy enough, I'm sure you've had that air filter out at some point by now and would have seen an issue there....nothing 'minor' in the air filter path will do this, it would have to be a sucked up plastic bag, etc.

This all leaves us with your fuel supply. We know there is fresh fuel in there so that is good, and eliminates a most likely suspect due to it sitting. However at this point we don't really know how much fuel is getting to the engine. If it seems rich then engine is getting overflow of fuel and if it feels low/lean then engine is getting less fuel then required.These can be confirmed by getting exact fuel pressure checked.
Looking at lean conditions, our first suspect to check is the fuel pressure. If the pressure is low we would need to first replace the fuel filter and see if there is any change (no way to test the filter). If the pressure is still low, then clamp off the return line to see if the pressure increases a lot indicating a bad pressure regulator. If there is still no change,
Then as for further troubleshooting and repairs we need to pull the injectors/rail and make sure they are not leaking off pressure. If all is well there, it is time for a fuel pump to get replaced.

But if the assume that the fuel pressure is OK.... well there isn't a lot to go on here apart from injector clogging/laziness to cause lean condition with adequate fuel. An intake leak is out of the question for the most part, as it would not prevent revving.

Getting all these possibilities checked and inspected will help to confirm the problem.

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