wackbards

iTrader: (2)

'91 with VVT swap running on MS3PRO

I completed an engine build/swap this spring, and now my car keeps dying. This was purely a mechanical engine swap, and the only electrical change I made was wiring in an oil temperature sensor. The stall is happening while cruising, or even just idling. It's been happening with the engine running for shorter and shorter intervals. The first time, it ran for about 20 minutes before dying. The second time, about 10 minutes, then 5 minutes, then 5 seconds. When it dies, the engine just stops without sputtering. After it dies, it won't start again for quite some time (20-30 minutes). No start condition has the following:

• cranks just fine
• FP primes
• all electrical appears to be working
• virtually no parasitic draw on battery with car off
• fuel smell out exhaust pipe while cranking
• cam and crank signal
• coolant temp signal
• AIT signal

I haven't yet checked to see if spark is working. I have GM COPs wired sequentially, and I'm struggling to picture what could fail all 4 coils at once and cause it to stall clean. Just full disclosure, I haven't tested it yet.


Here are things I've done & observed:
The first time this happened, I only had 1/8th tank of gas, and I thought I'd run out of gas. It happened again, so I thought maybe the OE fuel pump was on it's way out. Replacing the pump with a DW200 didn't cure the issue. I popped open and visually inspected the main relay and the fuel pump relay. The main looked perfectly healthy, but the FP relay looked haggard like some of the smoke had escaped so I replaced it. Having gone through all that, symptoms prevail. I can definitely smell fuel in the tail pipe after cranking/no start. I don't really suspect the main relay because it cranks, and the FP, primes and all electrical appears to be working while it won't start. I also noticed that TS was reporting low voltage during cranking which made me think I'd finally worn out my battery, so I replaced it. This didn't change the cranking volts as reported in TS. I checked the voltage at the battery with key on but car not running (12.48v) and at the injectors (12.25v). TS was reporting ~11.8v, so I calibrated battery voltage in TS so that TS batt voltage is mirroring what I read at the injectors. This appears to be a new issue. I don't recall my battery ever reporting anything but ~12.5v in TS. I've checked the grounds at the PPF, below the brake MS, the braided strap by the dipstick, and the main collector point where I ground everything else on the back of the IM.

At this point, I'm at a bit of a loss. This kind of electrical gremlin is my worst nightmare. I'm open to recommendations. I have logs of stall events and no starts if anyone has recommendations of things to look for.

wackbards

iTrader: (2)

No spark after it stalls. Laptop died before i could check cam/crank signal, but I've tested it during no start before, and it was producing both signals. All other electrical including fuel pump priming appears normal.

wackbards

iTrader: (2)

Also getting "SD error" in TS. Maybe an ECU issue?

curly

iTrader: (25)

hornetball

iTrader: (4)

As you know, I feel your pain (literally). My car now has:

1. A new ECU (the upgrade from 11-year-old MSPNP to MSPNP Pro was worth it for other reasons though);
2. A new fuel pump and alternator (hey, the car is a 1990 with 250K miles -- and the alternator was squeaking a little bit -- and the new components are "Lifetime Warranty" -- these are my rationalizations);
3. New main and fuel pump relays (they were a little crusty looking -- kept the old ones for spares + race car uses the same parts); and
4. Squeaky-clean grounds (finally, something that didn't involve an outlay of cash!).

And, still, the shut downs persisted and were becoming more frequent.

Finally, the car started doing it in the garage and after a shut down I could hear an electrical buzzing noise coming from the area under the intake manifold. I started plugging/unplugging stuff and tapping on various electrical devices. When I tapped the main fuse box, the noise stopped immediately. I was then able to start the car, wait until it stopped, and repeat the exercise. I unscrewed the main fuse box and lifted it to inspect the wiring. I couldn't really see an obvious culprit in the wiring, but inspecting the fender underneath the main fuse box there were a couple of bare-metal spots that looked like areas that had been arcing/shorting. I then proceeded to cleanup the wiring and main fuse box connectors, put plastic corrugated conduit on the bundle that runs along the top of the fender, and further secured everything with plastic zip ties.

I then went inside, told my wife to keep her cell handy, and did a 20 mile test drive near the house. No issues.

This morning, I drove it to work (40 miles). No issues.

I'm not ready yet to declare complete victory . . . but things are looking hopeful -- and it was REALLY nice to drive the Miata this morning, what a great driving car.

tl;dr . . . take a look at the fender under your main fuse box for evidence of arcing.

wackbards

iTrader: (2)

Thanks for the feedback guys. It's slow going trying to find time with an infant, and catch it in failure mode. I'll keep posting as I chip away at it.

wackbards

iTrader: (2)

Meh. Got it to stall twice idling in the driveway, but it fired right back up both times. Looks like it will never get the oil up to operating temp just idling. Hooray intermittent faults.

hornetball

iTrader: (4)

FWIW, I'm declaring victory. Mine was an intermittent short to ground underneath the main fuse box. Hooray old cars.

Ted75zcar

iTrader: (2)

Do you lose connection between TS and the MS when it stalls?

wackbards

iTrader: (2)

No loss of signal.

Ted75zcar

iTrader: (2)

What is your ignition setup

do you get sync errors

do you get full rpm sync when running

do you get a vvt error

post a composite log

wackbards

iTrader: (2)

But... Regarding HB's experience...

No obvious loss of insulation on any wires, but it does look like it's been rubbing. Bare metal is worn through on the fender.

wackbards

iTrader: (2)

Ignition setup is wired fully sequential from ms3pnp pro to d585 coils. I've never got sync errors untill stall has occurred (reason 32). I've checked for cam and crank signal during no start previously, and got both signals. I use falling edge. VV target & actual are tracking.

I've been hoping to catch it after a stall when it won't start to validate again that I'm getting cam and crank, but so far the past couple days it's been firing right back up after stalling. I've just been idling it in the driveway, so it might not be getting enough heat soak to really get the no start effect too kick in.

Ted75zcar

iTrader: (2)

It sure sounds like a cam fault to me. Could also be a crank fault.

try to confirm you are actually getting full sync on restart after a stall. Some MS configurations will fall back to a non-sequential mode if the triggers aren't synced during cranking.

wackbards

iTrader: (2)

This is one of the two stall while cruising events that drove me to replace the fuel pump. Here you can see that the first event is AFR's going full lean.




Here's a normal start yesterday. Nothing really to see here I don't think, just a representative start event. I've been trying to catch it after it stalls & won't start to see if I'm not getting cam or crank. I've got it to stall twice this weekend just in the driveway, but it started right back up both times.

wackbards

iTrader: (2)

Ok! Stalled, no start. Good cam & crank signal, but no spark in test mode.

curly

iTrader: (25)

Yeah you have a misfire right before it stalls in that log, I'm going with a spark issue. Try wiring in some VVT coils or similar and ditch the GM stuff.

wackbards

iTrader: (2)

I pulled apart the cop pigtail, and I had a loose butt splice on the power ground.

Ohhhhhhh man! I think this is it.

This is the second time I've found a loose butt splice. Time to up my wiring game.

wackbards

iTrader: (2)

Are you seeing the misfire because of that RPM jiggle right before it dies?? I'm just curious how you spot it.

curly

iTrader: (25)