Need some input...56k beware.

I'm in the process of tearing down my 90 I6 and I need some opinions on these pix...




What you are looking at is the #3 exhaust port to the left. To the right is the #4 exhaust port and intake port. Note the white exhaust valve and brownish looking port. What is up with this?





As far as the pic above, I'm pretty sure the sensor with the pigtail is the coolant temperature sensor. What I want to know is what is the sensor that is broken to the lower right?

Carbon buildup, maybe? Running rich too perhaps?

a lot can be learned from looking at your spark plugs. at the back of the Haynes manual there is a color page that shows the spark plug and a possible diagnosis of the problem. i would pull the plug and compare to the photos.

for instance:
ASH DEPOSITS
symptoms: dry sooty deposits indicate a rich mixture or weak ingnition. causes misfiring, hard starting and hesitation.
Recommendation: if excessive deposits accumulate over a short time or low mileage, install new valve guide seals to prevent seepage of oil into the combustion chambers. also try changing gasoline brands.

the above was taken out of the back of my haynes manual for my dodge ram but its the same for the XJ.

its a start and go from there.

hth
stewie

i think you broken sensor would have been the knock sensor.

wow that intake port is nasty lookin

As 90xj06 said, the broken sensor is the knock sensor (AKA detonation sensor). Replacements run $70+.

Looks like you've been sucking a lot of oil in your #4 intake. What do the other intakes look like?

The intake manifold as well as the rest of the intake ports look as disgusting as what you see in the pic. I do believe it's because of the rear valve cover hose that goes right into the intake manifold sucking all the blow-by in. I don't understand why only the #4 exh. valve is white. Also I've looked for replacement knock sensors and none look like what came off my 90. I may just omit the thing. Thanks for the responses.

Slo-Sho said:

The intake manifold as well as the rest of the intake ports look as disgusting as what you see in the pic. I do believe it's because of the rear valve cover hose that goes right into the intake manifold sucking all the blow-by in. I don't understand why only the #4 exh. valve is white. Also I've looked for replacement knock sensors and none look like what came off my 90. I may just omit the thing. Thanks for the responses.

Click to expand...

NAPA replacment sensors look a bit different, but perform just the same. Just make sure the plug is the same and you're good to go. The new sensors are two-piece, vs. old style 1 piece.

You can see the difference in the Knock sensor here:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

possibly you've got an EGR problem and it just happens to flo mostly to the 4th cyl? egr system does develop a lot of carbon. Just a possibility.

I won't know for sure until I disassemble the old motor, it also had a prominent mis-fire so I'm thinking maybe a blown head gasket ( it was pumping white smoke from the tail pipe). For now I have a 97 short block that will be taking it's place. A few differences that I noticed are that the 97 block has no provision for the coolant temp sensor or the knock sensor. Anyways here are some more pix...

The once venerable Renix...now scrap metal.




I will say one thing though...the Renix era XJ's sure do have alot of sh*t under the hood compared to their Chrysler counterparts.


The 97 shortblock...notice the 1/8" thick plate used as the stud girdle.

Well I got the old cylinder head off the old motor. I was surprised at what I saw....




Any ideas as to what may have caused this?