Help me remotely diagnose why my NA Miata has more trouble getting going than I have every morning

I'm used to my NA Miatas firing up after a couple of cranks and within a few seconds. Feels like they usually fire before they even complete the first full revolution of the engine - which I know isn't the case, but that's (what) it almost feels like it.

My current "this is the last on of these dang things that I'll buy (unless I find a really nice '95 M)" 1990 NA used to do that, too. Until I took it to Laguna Seca and it, well, barfed at least half its coolant out in the last session of Saturday. Oopsie. I also noticed that it had a bit of a "VTEC, yo!" kick at around 4k when I was standing on the loud pedal, and I don't think any of my other 1.6s had that. Not even the turbo one.

Local Mazda dealer in Seaside checked it over and replaced the blown hoses. It doesn't use coolant or oil, and the oil pan doesn't have stuff in it that looks like I'd put in on fries if I were from Belgium. However, ever since that incident it feels like I blew a bunch of remaining hamsters out of the exhaust (which is a fancy way of saying it feels a bit down on power) and it needs some serious cranking to get going. Not like "my diesel has no compression and no glow plugs" cranking, but a lot longer than I'm used to.

I first suspected the battery, but even fully charged and/or with the booster pack connected, no difference. Fuel filter is new, and it doesn't feel like it's out of fuel - OK, actually it feels like I'm cranking it to get the fuel from the tank to the carbs, only that it doesn't have carbs.

I guess it's time to check the fuel pressure and do a compression and leakdown test. Assuming I can find both the compression and  leakdown tester that are still buried somewhere in the moving boxes.

Fortunately there is no deadline attached, it's not like I want to go to the 30th anniversary Miatas at Laguna Seca in October or anything like that.

WWGRMD(iagnose)?

A few things: 

1: replace you spark plugs.

2: replace your coolant temperature sensor.

3: depending on how hot it was I would consider replacing the coil and wires. 

A thermal event at temperatures can play havoc on these things and while they may appear to still be operational I bet they are not doing so at 100%.

After that I would consider testing the catalytic converter, heat and RPM cause the carbon to fly from its previously cement like home into the cat.

In reply to BoxheadTim :

FWIW mine acted like that before the fuel pump died. Also mine has a bit of Vtec-Yo! too that hits about 4K. Having never owned a 1.6 before, I just presumed it’s a byproduct of having the timing advanced?

The 1.6 cams do wake up at 4k. The 1.8s don't, it's part of what makes the 1.6 a fun little engine.

If it's extreme, check to make sure someone didn't screw up a timing belt change and get the intake cam timing off. You can check that by pulling the valve cover and setting the timing mark to T. There should be marks on each cam gear right at 12 o'clock marked I on the intake side and E on the exhaust side. If you don't see them, rotate the crank one full turn. If it's off, it'll be off by a full tooth.

I'd start with the compression test. Overheat condition followed by hard starting and a lack of power? Yeah, compression test. The coolant temp sensor (the two-wire one on the back of the head) is pretty easy to test with a multimeter, but they're not failure-prone as a general rule.

The timing shouldn't be advanced on this one, but I guess I should have checked more thoroughly.

Throwing in a new set of plugs and maybe a set of wires on there can't hurt, and I don't think a new fuel pump would hurt that much either. The weather isn't really conducive to Miata experiments but hopefully it'll get a bit better next time I'm home for a little longer.

I'd check the fuel pressure before changing out the pump. I mean, it won't hurt, but it may not get you anything either.

Keith Tanner said:

The 1.6 cams do wake up at 4k. The 1.8s don't, it's part of what makes the 1.6 a fun little engine.

If it's extreme, check to make sure someone didn't screw up a timing belt change and get the intake cam timing off. You can check that by pulling the valve cover and setting the timing mark to T. There should be marks on each cam gear right at 12 o'clock marked I on the intake side and E on the exhaust side. If you don't see them, rotate the crank one full turn. If it's off, it'll be off by a full tooth.

It's more like "wake up with three shots of espresso". Probably a good idea to check the timing belt.

I'd start with the compression test. Overheat condition followed by hard starting and a lack of power? Yeah, compression test. The coolant temp sensor (the two-wire one on the back of the head) is pretty easy to test with a multimeter, but they're not failure-prone as a general rule.

Right, let's see if I can find the compression tester among all the other stuff that still waits to be unpacked. "Lack of power" is of course relative, but it definitely feels slower than my memory suggests it should be. And it did feel perkier before the trip to Laguna.

Keith Tanner said:

I'd check the fuel pressure before changing out the pump. I mean, it won't hurt, but it may not get you anything either.

Good point. Another excuse to buy more tools as I don't have a fuel system pressure tester yet.

I still didn't buy a fuel pressure tester, but I also couldn't remember where my cheapo NAPA compression tester went. At least I can remember where my much more expensive leakdown tester is...

Anyway, this problem needed solving, so onto eBay I went to look for Snap On or Mac Tools compression testers. Until I found this:

I have no idea if it works, but I was willing to blow a benjamin on it. So what is this odd piece of old German tool pr0n?

It's a recording/scribing compression tester made by MotoMeter:

Basically, you insert a blank chart and the needle on the compression tester scribes the measurements on the chart. There's a little lever on the back that allows you move the chart up as you move from cylinder to cylinder. Can't wait to try it out on the Miata. Only downside is that you need two people to do a compression test as the tester doesn't screw into the spark plug hole.

This thing even came with the original hand-written receipt from when the original owner bought it in Frankfurt, Germany.

One of the reasons I had to have it is because I remember back in the 80s in Germany, pretty much every self-respecting shop had one of these. They were way too expensive for a shade tree mechanic  - the receipts total up to about DM150-160 in what I think is late 60s/early 70s money, and that was a fair chunk of change back then.

My vote is a fuel pump or pressure regulator (or something in the fuel supply chain is giving up).

Failing fuel pressure caused the overheat (leaned out) at full song.

Failing to come up to pressure quickly causes long cranks (poor starting)

Reduced fuel pressure or flow is causing the sluggish power feel.

The coolant loss was caused by one of the small coolant hoses at the throttle body splitting. I know that for certain. Still doesn’t rule out the fuel pump as a reason for the starting issue. 

I’d try cycling the key a couple times to prime the fuel system before cranking it. See if it starts quicker 

I’d check the main engine ground and ECU ground too.  Poor starting is often electrical and in the starting circuit.