91 Legacy misses - no codes

[lmason2554]

Hi,

I'm new to USMB. I have a 91 Legacy - non turbo - that has a steady miss, poor performance and the cat. converter gets too hot.

The car acts like the ECU has gone to baseline as if a pimary sensor has failed, but there have been no error codes recorded. I have tried to perform the D-check but all I get is a steady flash of the CEL.

 

I have replaced the plugs and wires, checked for good fuel pressure, checked connections and wires at all sensors, checked vacuum lines ...

 

This is a good running Soob that is well maintained with 230,000 miles. Any suggestions or ideas?

[unibrook]

Is it misfiring under load, and only when the engine is warm?

If so, you might replace the front 02 sensor if that hasn't been done in the last 50k miles.

[lmason2554]

Thanks for the feedback.

 

It's running bad all the time, of course, we haven't had any really cold weather for a while so I don't know how it acts cold (below +10 F).

 

I did replace the o2 sensor less than 20,000. I did get error codes when that happened.

[bheinen74]

timing has skipped a tooth or more.

check timing to be dead on then proceed as needed to fix it. use the right marks, you use the back tick marks, do not use arrows.

[lmason2554]

Definately an interesting point.

 

Is this something that happens with a Subaru timing belt?

I've had timing chains on other vehicle do that, but I thought a timing belt would just break.

[Robert Harik]

if the timing belt didn't skip the check you compression ( you might have a tight or burned valve) The unburned fuel from the miss will cause your cat to overheat. When you replace the plugs were they carbon fouled /covered with soot? Were they all the same? Was your car running rich( poor gas milage , sooty exhaust before the steady miss started)? If the engine mechanicals check out and the missing is from fouled plugs then check you ECT( engine coolant temp) sensor( you said you checked the fuel pressure).

[lmason2554]

I did check compression, looking for a burned valve. Compression is good. The plugs I replaced all looked good, even burn in all cylinders. I'm confident spark and compression is good. I'm going to check cylinder 1 at TDC against timing marks to see if the timing is off.

 

Your point about the coolant temp is a good one too. I'm also going to check the coolant temp sensor. The thing that confuses me about that is I replaced that sensor less than 10K miles ago, but maybe its gone bad.

Edited February 28, 2012 by lmason2554

[lmason2554]

OK, I fixed it.

 

Here's the follow up:

 

After checking timing, compression and spark I finally determined cylinder #1 never changed the engine miss. With the engine running I pulled the plug wire - no change. Next I disconnected the plug to the fuel injector (with the engine running) - no change. I pulled out the specs. on the ohm readings for the fuel injectors. Tested all four. Cylinder number one had a bad reading. Replaced the injector and the car runs like nothing was ever wrong.

 

The moral to the story - If there is no error code check the ohm reading on the injectors.

 

At least that's what I learned from this story.

 

Thank you for all of the ideas and support.

[bheinen74]

that is good check back in to give later report.

injector didn't cross my mind, but i have had that once as well, so it should have been thrown out there too.

[unibrook]

Thx very much for posting your resolution! That will help the next guy.