Cycling Idle, bucking cruise.. car is now a rodeo
 

Hi Guys,

So this car has stood the test of time, including being shipped from the UK to Australia where i'm lucky to be. It's survived minimal maintenance and been squirted for 10 years, reliable and stable.

I've just gotten the car out of storage where it hasn't been driven for a couple of months.

Had to jump the car and it started OK but died immediately.
In the end to get her running, I had to unwind the idle screw totally- it's been set as it was for a long while.

Driving her home- horrible! See attached short log and msq.

Before this happened, it was beautifully smooth.. so what's suddenly gone wrong?!
So in summary:
- suddenly, idle is so low it stalls. Gets worse when car is warm
- had to jump it to get going (could the MS have been damaged?)
- basically the car holds rpm then suddenly dips and repeats. This isn't tach spike, i've had that before
- under boost- it drives well.. just terrible under vaccuum

What i've tried:
- Unplugged the idle valve that's regulated with pwm. No change
- Checked the air valve isn't stuck- no change
- Pulled the MS. Found the power connection corroded through possible moisture? I re connected it and checked all wiring. MS looks good inside, no leaky capacitors or visible damage
- Checked all earths
- Checked for spark on all cycls- yep
- changed the MAP source from the FPR to TB

So what do we think? I'm thinking:
- CAS fault
- Injectors? FPR?

Unfortunately the LC-1 sensor burnt out a while ago so no AFR.

Any help appreciated. Log isn't telling me the route cause.. so it's a investigation at this point.

Setup:
- turbo install
- MS1 with v3 board and usual mods for MX5
- NA6, 1992.

WAT??

haha- you know.. i put the O2 sensor too near the manifold. It got toasted after a couple of years. It just throws error. I've changed it's authority to zero.

Maybe it's time to fix that O2 sensor....

You have got to be fucking with us. If this some kind of epic troll move I commend you for such a long and intricate story.

10/10

??

Guys, i've set the wideband has no authority (i.e. it won't adjust fuel map, closed or open loop). I've driven with no wideband for 5 years.. after the dyno you never need to touch it.

You should also know that the stock narrowband O2 location is prone to overheating.. this happens to everyone.

Regardless, the car has been perfect in exactly this condition for years.. all of the sudden, if you look at the log we are seeing a crazy cycling/oscillating syndrome.

Hold the gas and it jumps up rpm, then suddenly drops to 900rpm... then jumps back up again.

Anyone think perhaps over a couple of months the fuel could have gone bad?

Will a video help?

All sensors look good.

Except, you know, the one designed to tell you how much fuel is going into the engine...

noted. To be clear though, that will tell me a symptom not a cause.

I guess i'll contemplate purchasing another one, maybe this time with a heatsink. Has LC-1 fixed the sensor failing problem? Not sure i'll ever use it with any authority.

In the interim... ironically my nose is (literally) telling me fuel.. i.e. injector, FPR, Fuel pump or filter issue.

Change out the fuel, look at plugs.
Also, could be your IAT seized?

You moved halfway around the world and haven't re-tuned your car, nor do you have a way for EGO correction to even make an attempt at compensating.

Yes, it's been dynod twice since moving to Australia. I'm not a total fool! More, i've just stopped worrying about fuel and spark maps after i've had a dyno.

Maybe this is more a belief than fact- you don't need a wideband O2 when you've burned a reliable fuel map.

Open loop would be the only real concern.. as we know.. AFR corrections are disabled for open loop.


Thanks I did notice the IAT looked static. This is a concern. Luckily it's not defaulting to -40 deg c. I'll check the wiring and a change of sensor is trivial cost.

Going to try some basics. I'll switch the plugs & HT leads as this could be as simple as a misfire. Will also burn down the fuel and re-fuel. Under boost she's pretty good and doesn't miss. More under vac/cruise it's horrible.

Why do you think it's the MS? Have you flushed the old ass fuel? Do all injectors fire properly? Are the spark plugs all fucking gummy because of the varnish that some people calls fuel after it's been sitting?
If it was running before, unless there is corrosion on your board causing weird shit, I'd say the problem is somewhere else.

I work with bikes that have been stopped for a while and usually new sparkplugs help a fuckton after you flushed the fuel.
Sometimes I have to take the injectors out and drop them in the ultrasonic cleaner for a while for them to run properly again. Shit gets gummed up quickly.

Sure i understand that you can run without a wideband. But my concerns were valid without the knowledge prior that you had tuned it since arriving in Australia.

Yes you can run without a wideband if you have a good tune. The problem is now that you are having an issue, and one of the sensors that could give you accurate information is not working. So you have zero idea what the AFR's are so its hard to actually give good relevant advice to what the issues are when we don't have the information we need to figure things out. Get the wideband replaced. Move it further away from the turbo, and add a heat sink to it so that it will last longer.

Also if the the IAT is not working right, the MS will default to reading 70degrees fahrenheit.

Looks like a giant vacuum leak to me. 67kpa at 1000rpm? Something isn't right there.

Also your fuel map looks way off.

https://cimg9.ibsrv.net/gimg/www.mia...9f57a69919.png

Idle cells look very low. You are running 10x the fuel you do at idle at 15psi. Should be more like 3x. Add some fuel down there and see what happens.

This was a great tip.

I upped the req_fuel and the car started to behave normally. However, I had to increase it from 8.8 to 25 (280% increase).

I thought i'd check my old tunes after the dyno and the fuel table is the same... so either we're looking at a hardware/mechanical reason or something went bad on the MS?

I changed the plugs, refueled and fuel filter today (and had a nice volume of fuel enter my ear, even tho i tried to depressurise the line by running with the pump off) no change.
Now it's been 'narrowed' to just fuel, i suppose the only remaining cultrpits are:
- Fuel Pump
- FPR
- Injectors

Curiously, when i run the original tune i've run for years, while it can't idle or cruise, boost is fine. With the high req_fuel boost is stumbley.

This is leading me to injectors.. maybe it would pay to run some cleaner.. perhaps they aren't atomising.

here's a log- check out that rock solid voltage (i'm proud of my earthing effort)

we aren't surprised -- your fuel map is trash.

you need to do the most basic of tuning...

Timing of this thread is brillant.

Just pulled my car out of storage last night after 6 months.
No power, misfiring, running like shit, afr's all over the shop.

I'm assuming its bad fuel - has 1/2 a tank in it tuned at 98. I'm thinking ill roll the timing back 4 degrees and top her off. Hopefully that's all it is. Maybe see if i can get some fuel additive...

Petrol station opens in 3 hours <- why did i have to store my car in the middle of no where. I have 700km to drive later today :rofl:

Dropped timing by 4, car drove fine to the station, I whacked in half a tank of 98, some injector cleaner and turned boost down from 14-> 8.
All good, time to head off.

This drive should clear out the tank and ill return her to normal.