Seems like it's time for some engine maintenance, opinions?

Hey guys, I have a few issues with my '94. Let me list them and see if you can think of things that might be causing them.

1. Starts great, even when dead cold. But, when it's cold, the engine has much less power; it's a real "dog". It's a rough, back-firing (through the intake) start when I leave the driveway usually. When the engine gets some heat, things smooth out.

2. Generally the car is sloooooow. I know Miatas are not rocket ships, but it seems the engine has a big flat spot around 2500 RPM, going to around 3500 or so. It feels like it's going lean.

3. It's not an issue now, but the car does want to get hot in the summer. Extended runs at 3000+ RPM in 5th gear cause the car to slowly get past the ideal point on the temp gauge. When that happens, it pings at full throttle. A lot.

4. The oil pressure seems low - about 38psi max when hot.

Now, here's what I've done so far:

1. new plugs and wires
2. new radiator (bigger core, all-copper), plus new hoses and thermostat.
3. sheet metal work to make sure the most air goes through the radiator (that helped quite a bit for the overheating)
4. Set the timing to 8deg (two less than stock) to avoid pinging - that helped, but probably it explains, at least in part, the weakness of the engine. Advancing the engine past 10deg causes massive pinging.
5. New battery (not that that would matter much here).

The engine does not smoke, it has good compression, and it doesn't leak. There's no water in the oil or oil in the water, and it doesn't "use" coolant. The fans work (and they are ganged together). The air filter is new.

I bought the car a year ago, and I've been picking away at the little things since then. I'd sure like to civilize the engine a bit. Any ideas?

Start with Seafoam...

Set the ignition timing by ear, rather than with the light... Then measure it with the light... The pulley may have moved. It's also possible that your cam timing is off by a tooth.

How old is the timing belt? Water pump? If cam timing is off a tooth or the pulley has slipped and your water pump is weak... it may be "minor" maintenance.

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Originally Posted by tailchaser

Start with Seafoam...

Set the ignition timing by ear, rather than with the light... Then measure it with the light... The pulley may have moved. It's also possible that your cam timing is off by a tooth.

How old is the timing belt? Water pump? If cam timing is off a tooth or the pulley has slipped and your water pump is weak... it may be "minor" maintenance.

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I know the pulley has not slipped, because I put a dial indicator down #1 cylinder and checked TDC against the mark on the pulley. Still, I basically followed your advice (in advance) by attempting to tune the pinging out of the engine.

Cam timing off - certainly could be.

The components (including the cam belt) are most likely old - I bought the car with 88K on the engine, and I doubt the previous owners were maintenance mavens.

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Originally Posted by mvalant

I know the pulley has not slipped, because I put a dial indicator down #1 cylinder and checked TDC against the mark on the pulley. Still, I basically followed your advice (in advance) by attempting to tune the pinging out of the engine.

Cam timing off - certainly could be.

The components (including the cam belt) are most likely old - I bought the car with 88K on the engine, and I doubt the previous owners were maintenance mavens.

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By "tune by ear"...

Jump ground & ten (same pins for timing light, check if you're not sure, cause i'm sure not)
loosen the bolt
move the doohickey back and forth
you'll have a wide space where the engine runs smoothly
On either side, the engine will slow down
place the doohickey smack between the rough spots

But... if you've already checked TDC, probably no point in that. I'd still not sweat much until you Seafoam it.

OK, I Sea Foamed the engine twice according to the directions listed in other threads (let the engine suck the liquid out of the can and keep it running with the throttle body). I also put a can in the gas.

Result: the engine does run more smoothly, no doubt. The weather warmed up, so we'll see what cold morning running feels like soon enough.

However, I can still not run the engine at the 10 degree mark - about 8.5 or 9 is all I can get. Considering that lots of folks run the engine at 14 degrees, this is still a bit wierd. Still considering the oil pressure is at 37 hot, do I really want to make more power?

Getting the #1 piston to TDC has NOTHING to do with valve timing. Pull the front cover(s) and check the cam marks. I bet it's jumped a tooth, or two.......

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Originally Posted by MadMerv

Getting the #1 piston to TDC has NOTHING to do with valve timing. Pull the front cover(s) and check the cam marks. I bet it's jumped a tooth, or two.......

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Well, I was speaking to the ignition timing when I posted that, but yes, I will pull the belt covers off, and check the timing there too. I need to check the belt condition anyway.

OK, I've now checked the cam timing.

Here's the cam timing marks:

http://engr.smu.edu/%7Emvalant/timing1.jpg

And here's where the crank timing mark wound up for the same setting:

http://engr.smu.edu/%7Emvalant/timing2.jpg


So it looks to me as though the cam timing is OK. Am I wrong? The cam timing marks stamped into the sheet metal aren't exactly crisp.

The belt sure looked good, but that doesn't mean much.

I did reset the belt tension, because the belt was a little loose. It deflected about 9/16" instead of the 3/8" quoted in the Haynes manual. However, I guess a new belt is the best idea.

I know there's supposed to be a certain number of 'open' belt teeth between the 2 cam gears. Have you checked that? (Not sure of the number, but I'm sure it's easily found on miata.net)

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Originally Posted by sammm

I know there's supposed to be a certain number of 'open' belt teeth between the 2 cam gears. Have you checked that? (Not sure of the number, but I'm sure it's easily found on miata.net)

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Yep, 19 teeth. I'll be changing the belt tonight - I've got the whole procedure printed out now, more or less. It certainly looks easier than the Alfa Romeo V6 cambelts of years past...

Well well, I moved the remaining parts out of the way, and had a look at the crank sprocket mark verses the cam sprocket marks. Oops, the previous owner (or his mechanic) got both cams one tooth advanced, according to the marks. I bet that's why the engine didn't run as well as I thought it should.

Now the engine looks to be timed properly, with a new belt in place, and I did it according to the proper method. Got my fingers crossed that the engine will run better, too.

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Originally Posted by mvalant

Now the engine looks to be timed properly, with a new belt in place

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Good work. :clap: I'll bet it runs likes a top now!

Almost sounds like the previous owner might have used Miata Technologies for servicing. :rolleyes:

Glad you found something! BTW... If anyone has difficulty setting timing, I've got one of the bracket made by the guy in NC that brings the timing marks out so they're easier to line up.

yes. Yes. YEEEEESSSSSSSSSS!!!!!!!!!

Oh holy frijoles this thing runs better. Now with all new belts and a couple of new rubber hoses on the PCV tubes, too.

Wow, driving to work tomorrow will be MUCH more fun.

You're welcome..................

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Originally Posted by Titus

Almost sounds like the previous owner might have used Miata Technologies for servicing. :rolleyes:

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:clap:
Although it doesn't appear as if he's missing enough parts for it to have come through there... ;)

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Originally Posted by MadMerv

You're welcome..................

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Yeah, I expected to see one of the cams in the wrong position, but not both... thanks for pointing in that direction.

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Originally Posted by Monkey of Death

:clap:
Although it doesn't appear as if he's missing enough parts for it to have come through there... ;)

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Still got the limited slip and all of the braces, heh.