Misfire without code need help

[LoudHoward]

Hello,

sorry for my english. My name is Christopher and I'm from Germany.
My wife drives an Chevrolet Lumina with 3.8L V6 from 1998.

We have about an month problems with cold starting misfires.

Misfire Video 1

I checked all vacuum lines, but they are ok. I found loosen EGR bolts. I ordered new gasket replaced, and fastens the bolts.

Now if the Lumina stands about 2 days the engine misfires on startup and is ok when engine warmup.

I record some values and see Bank3 (I think is Bank2) has high longterm fuel trim. But if I push the engine to 2500RPM the engine runs rich.

All OBD Values

Short / Long Term focused OBD

Thinks we replaced the last years:

- EGR Valvo
- Upper and Lower Intake Manifold gasket
- Upper plenum
- Dex - Cool
- New ignition wires
- Spark plugs
- PCV Valve
- TPS Sensor
- Oil and filters
- EGR Valve and gasket

In 2009 we had the misfires problem once or twice a year when the weather is cold. Then it was gone for the rest of the year.

Now its every second day. Coolant is not loosing.

Thx for reading.

Regards Christopher.

 

[Trav]

What OBDII codes does it have?

GM used 2 different injectors in these engines. The earlier ones used Multec and somewhere around 1999 they went to a Bosch unit.
The Multecs were very trouble prone units and can cause symptoms as you describe.

The Bosch are the better units and can be identified by their full metal body with plastic tops which are usually grey or black.
The Multecs are metal on the bottom only with most of the body being plastic, it also has a more rounded shape.

If this has the throttle body mounted MAF sensor they were also know to be source of problems.
As the engine has misfire in open loop I am thinking a possible injector issue.
Try a bottle of Liqui Moly Pro Line fuel system/injector cleaner and see if there is any improvement.

 

[LoudHoward]

Hi Trav,

no OBD II codes stored or pending. I have black injectors with plastic head and foot and metal body.

What I forgot the misfires are just on idle and lower rpm.

 

[Trav]

It sounds like a sticking injector when its cold and working better once warm in closed loop, that would explain the lack of codes.
Try the cleaner. Pro Tec also has a very good cleaner which may be easier to find, you want the red can.

I will look for a picture of the Multec. Try the easiest and cheapest solution first.

 

[LoudHoward]

Here one Picture of stock fuel injector by GM:

And a aftermarket because one injector was broken after lower intake replacement the plastic is broken when I want replace the lower o rings.

 

[Trav]

Those are the Bosch units, no real issues with them. You may still have one thats sticking a little, no injector is immune.
They usually do clean up easy enough with good results, a bad one would be rare.

I have the plastic parts, filters and seals for those in stock (as well as most other injectors). If i don't have them in Germany already (Nürnberg) i can get them there in a few days if you ever need them.
Did this start after you installed the aftermarket unit? Is this a so called rebuilt?

Edit: spray some start pilot at the bottom of each injector and see if there is a change in idle. You may have a nicked O ring.

 

[05LGTLtd]

Does this Chevy have a idle air control valve? Housing could be fouled with carbon?

 

[demarpaint]

Originally Posted By: LoudHoward
Here one Picture of stock fuel injector by GM:

What's the deal with that taped wire? Is it damaged? Any chance its arching causing the miss?

 

[Barkleymut]

My wifes van had a similar problem, started with a very small misfire and then got worse. Turned out to be the ignition coil. My other suggestion would be to check the Idle air control valve.

Good luck, and your English is pretty good. Much better than my German.

 

[Chris142]

My Moms car did something like that. It was a headgasket. Hers did lose a small amount of coolant over a few weeks. Very small like a cup/8oz.
A couple of gm stop leak pellets fixed it for now. A used oil analysis will tell you if its a getting a small amount of coolant or fuel in the oil. the only german I know is mercedes and volkswagen

 

[The_Eric]

demarpaint, good eye. A definite possibility.

LoudHoward, sometimes an easy way to catch a sticky injector is to take a mechanic's stethoscope (if you have one) or a long ratchet extension/long screw driver and put on the body of each injector. You should hear a defined ticking noise. If you hear one that's fairly muted in comparison to the rest, then you know something is up with it. A note however, make sure to "listen" to each injector in the same spot on each one. The sound will change from place to place on the injector body and can give you false impressions.

Another thing you can do is to read the resistance across the two pins of the injectors and look for the odd man out. If I recall, these usually measure 12-15ohms? Trav would know for sure.

 

[demarpaint]

Originally Posted By: The_Eric
demarpaint, good eye. A definite possibility.



Thanks- That's where I'd look first since it is the easiest, then follow the other suggestions in this thread if the taped wire leads nowhere.

 

[doitmyself]

My guess is that he is just conscientious and was worried about the plug wire abrading against the injector....my two cents.

Even though the plugs wires are relatively new, there still is a very slight chance that maybe one has internal damage that is resulting in intermittent mis-fire. I had this happen without a code being thrown.

Sometimes I miss the obvious because I make bad assumptions during the diagnostic process.

 

[Trav]

Quote:
My guess is that he is just conscientious and was worried about the plug wire abrading against the injector

That was my thought. The other thing is this has been going on for a couple of years on and off. Only when cold and in (i am assuming in open loop) and only at idle and low RPM.

It could be a couple things for sure but i am curious to hear if this started close to the time he put the replacement injector in.

 

[LoudHoward]

Hello,

the taped wire is just for protection. Wires are new ones and I want just prevent failures.
The screw driver test did I've done. I hear the clicking sound from all fuel injector. I tested all injector and all 6 have exact 14.4 ohm. I think this is perfect.

The symptoms was there before the new injector was bought.

But I will buy some fuel injectors cleaner and on this day the car did not make misfire I will drive a trip on highway.

Are there any tips to test the PCM?

Regards Christopher.

 

[Trav]

PCM failed/failing would have a code like P06xx. As long as the PCM was not flashed with a tuning file i wouldn't suspect it has issues.

 

[LoudHoward]

Is the upper intake plenum an factor for misfiring? Or is the lower gasket for vacuum? Maybe the new updated gasket is blown, or upper intake plenum.