'99 2.8 Roadster not running right (details inside)

[LannVouivre]

Mr. Bingley, get out of here with that logic!

[Mr Bingley]

I know--my bad.

[JKuhn]

Like I said, I'm getting the car tested today.

EDIT: The results are in. When I checked the coolant level this morning (after driving two days without topping up) there wasn't a noticeable drop. The radiator shop felt the hoses for abnormal pressure, smelled the steam when they opened the tank (not chemical, but the entire test was free), and did a pressure test. There wasn't any signs of combustion gasses in the coolant, and no water entered a cylinder. The clamp I tightened this weekend still leaks a bit, but not much, and I'll just tighten it a bit more.

They did however point out that the fan clutch is done for, and told me that they love BMWs due to how the gauge only climbs above normal when it's too late (as a warning to be careful)

[deni2s]

Great! Good as new then!

[me77]

...that they love BMWs due to how the gauge only climbs above normal when it's too late (as a warning to be careful)

2nd gen Miata‘s are the same, the gauge stays in the same spot over a wide temperature range. You can save the engine if you just noticed the gauge starting to move and do the steps necessary (AC off, heater on full blast). Many cars have dampened gauges like that for some reason.

[LannVouivre]

They're like that so customers don't panic and harass the service department whenever the gauge moves and isn't dead-center and completely stationary 100% of the time. It's a buffer that is supposed to encompass the entire normal operating temperature range or something, at least the above was the explanation from my Ford literature.

[JKuhn]

But at the same tiem it makes a gauge useless. The whole point of a gauge is to see just how high/low the temp is, so you can take steps to protect the engine BEFORE it's too late.

[deni2s]

You can save the engine if you just noticed the gauge starting to move and do the steps necessary (AC off, heater on full blast).

Not sure if AC off is the best option, as AC on engages aux fan for additional radiator cooling.

- - - Updated - - -

But at the same tiem it makes a gauge useless. The whole point of a gauge is to see just how high/low the temp is, so you can take steps to protect the engine BEFORE it's too late.

When gauge moves over the middle it's not too late. Most of the time even when reaching red zone it's still not too late. So let's not panic over that.

[JKuhn]

Speaking of temp gauges, do your cars also sit slightly over the middle? Mine climbs a bit over the middle mark, and then it stays there.

Back on topic:

I was wondering about something. As you all know by now, the car threw oxygen sensor codes (behind cat, no signal). The cats are no longer there, but it does have sensors in the pipes (before it becomes single pipe). Might that cause these issues? I'm still thinking about the cam timing, but by my reasoning such an issue would not cause the car to intermittantly run right. So because of that I'm thinking a sensor, or a combination of sensors.

[LannVouivre]

On newer cars, the rear O2s get factored in for managing the catalytic converters efficiently. It's not the case on these.

Did you ever test the cam sensor circuits at all?

[JKuhn]

Not yet.

So should I just leave the oxygen sensors as-is?

[deni2s]

Speaking of temp gauges, do your cars also sit slightly over the middle? Mine climbs a bit over the middle mark, and then it stays there

I suspect that depends on how precise is thermostat? One of my cars is straight in the middle the other is a bit over.

- - - Updated - - -

The cats are no longer there, but it does have sensors in the pipes (before it becomes single pipe). Might that cause these issues?

No.

[JKuhn]

Now I'm wondering about something else.

I just filled the petrol tank in the Z3, and the car ran great again. As stated before, this is not the first time it happened. After reading up on it, I'm wondering. Can it be that the petrol cap is faulty, creating a vacuum in the tank (along with the evap system)? Anyway, I guess I'll keep an eye on it, and open/close the cap when the performance disappears again to see what happens. Worth a try, right?

[Randy Forbes]

Was there a big inrush of air when you removed the gas cap? If not, then not as likely...

Gas caps themselves haven't been "vented" since some period between 12/31/1967 (the biggest implementation of vehicle pollution controls) and 8/30/1973 (when I purchased a new MGB with "evaporative loss control, aka the charcoal canister).

So while the Z3 does ingest its own fuel vapors, the canister and or lines would need to be plugged, or the gulp valve not working (that would almost certainly throw a DTC).

Doesn't hurt to keep thinking though, eventually you'll hit on the right diagnosis!

[JKuhn]

I don't know about the rush of air. We have fuel attendants here, I just unlock the cap for them. I'll try to see soon though.

And since you're here again, could you perhaps give your opinion regarding my previous question about the reinforcement kit?

[deni2s]

Now I'm wondering about something else.

I just filled the petrol tank in the Z3, and the car ran great again. As stated before, this is not the first time it happened. After reading up on it, I'm wondering. Can it be that the petrol cap is faulty, creating a vacuum in the tank (along with the evap system)? Anyway, I guess I'll keep an eye on it, and open/close the cap when the performance disappears again to see what happens. Worth a try, right?

Not the case here. I had driven the car without the cap (lost it at fuel station), no issues at all. Also evap system does automatically a couple vacuum leak tests, so would throw some DTC if there would be something wrong. So what is the situation with your DTCs after driving for some time with that "charizmatic" engine? DTCs can say a lot, but also the lack of DTCs can say something...

[JKuhn]

I haven't done another test. I'm thinking of buying a scan tool, but it might have to wait a bit depending on cost.

[deni2s]

All you need is:

https://www.ebay.co.uk/itm/Super-WiF...EAAOSwVRpZnpUu
to use with mobile or
https://www.ebay.co.uk/itm/USB-Cable...cAAOSw5YNZuko5
to use with software (INPA)on your laptop.

And don't forget this one:
https://www.ebay.co.uk/itm/20-Pin-To...oAAOSwX~dWnfEo

Not too expensive.

[JKuhn]

You're right that it's not very expensive, but ordering from overseas means it will take at least a month to get here (one month even for expensive USPS options, I can only imagine how long free shipping from China will take), and there will also be import tax. And the adapter doesn't ship to ZA anyway.

I'll see what it will cost to get something locally. And by the way, that phone one won't help, because I'm using WP8.1.

[deni2s]

There are plenty of other options on ebay (talking about shipping restrictions), but you got the idea. If you have a laptop with that cable and some IT skills, you can do everything what other scanners are doing and much more. Chiptune, etc... So great investment in long run.

[JKuhn]

I tested my theory, and it was not the case (as you both said).

Going back to my previous suspicion of the car overfuelling, what's the chance of a bad MAF causing this? I haven't added this to the list yet, but the exhaust does gurgle a lot when coasting, and lately I've noticed that it will sometimes (not that often though) give a single (at least that I can hear, this exhaust is rather loud and deep) pop when I start to accelerate.

[LannVouivre]

Yes, a bad MAF can cause it. I'd recommend trying a used OEM one for testing that, as the MAF is pretty expensive and aftermarket can really screw you over with weird malfunctions (I'm looking right at you, Bremi). It's really, really hard to figure out what's up if you can't see your fuel trims and other PIDs.

What you should definitely not do is throw a MAF on it without confirming it's the problem. You had the timing problem, right? Because that also causes fueling problems if the car is trying to inject fuel for misinterpreted cam position.

[JKuhn]

I'll keep that in mind.

To test the MAF, I can just disconnect it and see if that helps, right? As I understand if the MAF is disconnected the DME should default to decent (but not great) driveable fuelling.

EDIT: Updated the OP.

[deni2s]

To test the MAF, I can just disconnect it and see if that helps, right? As I understand if the MAF is disconnected the DME should default to decent (but not great) driveable fuelling.

Yes, just disconnect with engine off.

[LannVouivre]

All disconnecting the MAF does is switch to those default driveability settings and sit in open loop, which won't really help you tell if the MAF is bad. That's just telling the ECU to basically ignore the input of all the other sensors as well, which will probably muddy the problem. You really need to get a scanner and see what the car is seeing.

Or pay someone to take care of it if you don't want to do this in a logical or methodical manner.