m103 2.6 down on power and running very poorly when cold

[Mighty190]

The 2.6 in our 1989 190 is having a few issues.

- It does not seem to be making as much power as it should once warm

- If driven before it gets up to 80c but over 50c it misfires at full throttle and can barely do 80mph

- If between 50 and 80c it is very hard to start and will misfire on one or many cylinders for the first few moments of operation

- Once warm it does start easily and run smothly. Just slower than 160hp should be in what is now a 2,400lb car. Occasionally has a sudden surge of power right before redline.

- I have no reason to suspect a mechanical failure such as jumped timing or burnt valves with the engine as it idles fine and seems to be happy but slow once up to temp.

Things we have done:

- Swap OVP with a known good one

- Ran it with the ECU unplugged and it runs about the same. Maybe its stuck in some sort of open loop. ABS computer seems to still function.

- Replaced 02 sensor before all this was happening

- Exhaust is far from stock with no cats and was done this winter. This may be part of the problem but I remember it doing this before we parked it for the winter and built the exhaust.

- Does not seem to be a vacuum issue

The current theories are that its running in open loop or the engine thinks its at 120c or something. What is a good way to go about testing if its in open loop and what could be causing that?

[Mike Murrell]

Check Engine Light?

What brand of O2 sensor did you use?

[92-2.6]

Is your EGR valve working? You'll need a MityVac or similar to test if the diaphram holds vacuum.

[Mighty190]

The 02 sensor is a bosch 3 wire sensor and I am not sure if it is sending a signal for a check engine light. This is in our track car that was going to have a check engine light one way or another and was removed.

I do not know if the EGR valve is working. How would I test that? There is not an EGR on the manifold like a M104. Does this engine even have one?

[92-2.6]

If you do have one you would test it using a MityVac or similar to pull a vacuum on the valve.

[Ferdman]

190, when was the fuel filter replaced last?

[Mighty190]

We replaced the filter recently too. I forgot to add that.

[Mike Murrell]

EGR valve is mounted on exhaust manifold. Go to this sites parts catalog for a pic.

How old is the fuel pump?

[oldsinner111]

plugs,wires breaking down,coil?cap rotor?

[optimusprime]

All as above Oldsinner hit it on the head , simple maintenance first . Or get a diagnostic auto guy to find the problem .You can spend lots of $ and be wrong . I had a problem last year, and rather than spend cash on it , and not knowing just what it was . He came and found it right away .The coil was shot . I could have put all new parts on it till i found the problem .And would cost quite a lot to fix it .And the coil would have been last on my list.

[oldsinner111]

my m 104 one time was missing bad,could not figure,then I remembered I cleaned the motor.i had a plug cylinder full of water,and the plug was having trouble firing.

[Mighty190]

Ok so there is definitely no EGR on the manifold. Maybe its year or maket thing but both manifolds have nothing on them. Plugs and coil and all that seem to be fine and I find it odd that this issue seems to be so dependent on engine temperature. I also find it odd that it runs about about as bad with or without the ECU plugged in. That's telling me there is an issue with the controls. I just don't know how to test that.

[oldsinner111]

is the computer fuse protected?

[Mighty190]

The computer has the OVP relay which has been replaced.

[Rick76]

No EGR on the '89 M103 Federal engines.

Coolant sensor at back of head? Two thermistors, one for the engine computer and the other for the ignition module. Can be checked with an ohmmeter to ground and the resistance compared to values shown in the sensor curve graph. Example: +20 degree C = 2.2K-2.8Kohm, +80 degree C = 290 - 370 ohm.