VERY high EGTs and CHTs

[eec564]

Long story, just because I'm trying to provide detail and history.

 

The current tune on the car is: Base timing: 12 degrees. AFM leaned out about three teeth. O2 sensor dissconnected (last week, all it did was improve MPG by 2). Aux air regulator blocked off as it made noise. It passed its last smog test with average (for the vehicle catagory) NOx at 15 and 25, and very low CO, took a total of 1min, 30sec to pass on the dyno, for both speeds, I timed my ignition to 10 degrees for the test. Otherwise stock engine. New cap and rotor (napa). 14 city, 19-20 highway MPG, and I drive not-so-gently.

 

The story:

A little bit ago, I notised my Z (82 N/A, 5psd, basically stock) was running hot. The temp gauge would creep up to the center while cruising at 70, and even higher while cruising at 80. If I floored it and cruised at 110+, the car would start to overheat. Shortly thereafter I notised my exaust maifold had a cherry red glow to it after I drove it hard. I figured this out when I popped the hood at a gas station to check my oil while I was filling up. Not good, and high EGTs would explain why the car was running hot. Before this started, my CHT would stay down to where my thermostat would start to close. If I slow down to 55, my CHT drops back to just below half way on the temp gauge driving in 85 degree weather.

 

I thought that the problem could have been related to some exaust work I had done to the car. Upon examining the work, I found my 2-1 collector was partially restricted. I got myself a nice (read: cheap) little welder and took last weekend to fabricate myself a new piece. Didn't help one bit, and while I had the exaust off my car, I notised I've managed to melt my catalytic converter. Well, just the inside. Luckily, I don't have to pass smog until december of 08.

 

I've pulled my plugs, and they show signs of running rich (before I changed my AFM, I'm presuming) and signs of running lean, which look more recent. I'm going to pick up another set of NGKs when I have a short break from school and clean my room for spare change.

 

So anyone have any advice, questions, or want to point out something stupid I'm doing or haven't done?

[BrandonsZ]

what you are describing is typical of a lean condition, turning your AFM lean was the mistake. You could have gotten about 10% increase in mileage running lean instead of rich, but obviously you've paid the price of the cat and possibly other things.

 

Yes if you run lean you WILL run hot, and red hot manifolds are s sure sign. Search the forum for a more detailed explaination if you do not get one here.

 

Oh and yes you will eventually damage you engine by running lean which is why usually we run a little rich to be safe.

[eec564]

I checked the AFR on a smog machine, and the setting the AFM is on now is where it passed smog easily. The CO was high when I first bought it, before I leaned it out. The car ran great and then all of a suddon started doing this, with no changed made within a month or more.

[eec564]

Well, something changed. Sunday, while driving back from Davis to the bay area, I felt some change in the way the car ran. The temp gauge still stands straight up while cruising, but I can cruise up to 85 without overheating. Much more than that and it starts to creep back up. My manifold still glows when I'm driving hard.

 

I've no clue what or why. Anyone ever see something like this? Comes on and changes randomly with no changes made to the engine at all.

[cygnusx1]

At this point, you need a voltmeter, ohm meter, and a service manual. Start measuring the specs on all your sensors. Check, clean connectors, grounds, and check fuel pressure. Set base timing by the manual.

[Guest djm]

your cat is clogged. gut it (you need a new one anyway) and see how it drives. glowing manifolds are a dead giveaway.

[eec564]

Here's what's new on the car: Plugs (few hundred miles), cap, rotor, O2 sensor (those have 14K miles on them, in 8 months). I've checked the resistance of the CHT and IAT (at the ECU), fuel pressure is 36, timing is at 10.5 degrees. The engine runs FAR better with a bit more advance on it. I know my cat isn't clogged, as I've recently had it off the car. In fact, it has a hole burned through it. I have no idea how it passed smog like that, but it did. I've also scoped my ignition coil and the output looks good, and ran a DAC in the car with me tapped into my O2 sensor wire, and it cycles between rich and lean very quickly, exactly within the range it should. I've also had the exaust off the car for some welding, and I checked it for obstructions, but there are none. I'm still fairly stumped.

 

After driving it back from davis, and it starting to run better, things are marginally okay. It still runs hot (starts to overheat, but I don't let it) if I run at over 90mph for extended periods of time, or make a 5 mile run at WOT. I'll check back in once I get a chance to pull my new plugs and see what they look like.

[eec564]

So, I finally got a chance to check under my hood right after driving fairly hard. Up until now, everywhere I went had a bunch of slow city street traffic that let my engine cool off. My manifold still has a slight glow to it, and my engine temp is now back where it was when I bought the car. In the mid-40s weather we had the other night here, I never did get the car fully warmed up to get anything decent out of the heater when I drove my girlfriend home.

 

I also checked my spark plugs, and they have a slight dark brown spot on one side of the ceramic (after 300 miles on the new set) and the electrode (not the tip, but the part you move when you gap them) is black, but with a slightly white coating (that doesn't rub off by hand) on the top. That is, with the top as seen with you holding the plug upside down, looking into it, the side that sticks farthest into the engine. I can get my hands on a digital camera and post a picture if you all think it would be helpful. Thanks again for all the advice.