Gents,

I'm doing two back-to-back events at VIR. The weather is glorious. Unfortunately, about 2.5 days into my four day soiree, my car started running like crap.. Again. This has happened before. After several hard sessions, she'll start having high idle AFRs and running almost like she's out of balance. Today, I heard what I thought was a misfire on track. The session was nearly over so I came in. She wasn't idling smoothly. I checked plugs, plug wires, electrical connections, etc., then went out with my students. The next time I took her out, she did a beastly 25 minutes without issue. She ran beautifully. When my next session came, it was back to the high idle AFRs and the rough running on track. Weird AFRs at boost.

Help. I have another beautiful day at VIR tomorrow.

Thanks,

 

That's a lot of views for no replies. I suspect I'll have some cats deducted.

Thought I'd provide an update.

The car ran great at the track the next day. No issues for three hard 25 minute sessions and two shorter times out giving rides. I packed up and headed home, stopped for gas and coffee. She was purring like a kitten. I'm doing about 60 mph at 3200 rpm or so with AFRs in the high 13s low 14s, when suddenly there's a stumble like 200 pounds had been added to my trailer and the AFR shot up into the 17s. I pushed in the clutch and fanned the throttle a bit. AFRs swung wildly up and down, then she just started running perfect again. That happened one more time.

My route home takes me on back roads through some small towns. I'm outside of Ivor VA doing about 55 and it does it again, but won't come back. I shut her down and parked on the side of a country two-lane with my flashers on waiting to get hit by a sleepy truck driver. I waited a few minutes and tried cranking her over. She started. AFRs in the low 14s, but I could not get any substantial rpms going. I limped into Ivor doing about 15 mph and it just started running again. I eventually made it home.

Seems like my less-than-two-year-old DW300 **** the bed, but I'd appreciate some feedback. I'm running the Flow Force 625 injectors.

 

When was the fuel filter last changed? It could be getting clogged.

 

I was going to post the same, but held off to think about it more. If the fuel filter where clogged, then it wouldn't be so intermittent, right? Neither would clogged injectors, it'd just be bad all the time. Almost sounds like wiring/pump related, but then again, last time I had this happen to me I replacedthe pump, filter and fuel lines and never had problems since. Filter would be the cheapest and easiest to try.

 

You might also try to log it from the MS3, just to see if some basic sensor is getting flaky and feeding the MS bad data.

I would not suspect the fuel injectors. It's not likely that they'll all go bad at the same time and then "recover." The other comments regarding fuel supply are more likely.

 

I had an IAT sensor go bad (actually was the solder joints on the board) and it told megasquirt air temp was 300° so it pulled 20% fuel and ran lean as hell. Wasn't intermittent though.

 

The '99's can have Cam sensors that can fail intermittenly, depending on heat. They are also prone to having coil packs start to fail with heat. You can try a data log next time it running poorly and check for sync losses from the Cam sensor dropping out. I know more than a few people who carry a spare Cam sensor at the track. The '99 fuel pumps have been known to fail as well. Good luck!

 

Gents,

The car sat for about 20 hours. I came home from work today and kicked her over. She started normally and ran smooth as silk. WTF?

 

I doubt it's a cam sensor, when they fail it's not just a reduction in power, the engine actively shuts off when the MS3 loses sync and maybe restarts a half second later. It's violent, and the MS3 will light the CEL after it's gotten more than 2 sync errors.

Intermittent coil failure could make sense, the unburned gas is ignored by the O2 sensor so it sees all the oxygen that wasn't used and interprets that as being lean. Since the NB is waste spark, losing one coil takes out two cylinders so you lose significant power. It also dumps a ton of fuel into the cat (if present) which will destroy it in fairly short order if you keep driving it in that condition.

Losing the fuel pump or regulator intermittently could do it too -- need a fuel pressure sensor to be sure. Those are pretty easy to add to the MS3 and data log.

--Ian

 

Coil packs?

 

Coil packs heat up and fail intermittently. When there is a misfire it registers a lean AFR.

 

My 99 will start acting up after a few autox sessions, it will develop a hiccup around 5k rpm at full throttle, then if continued to drive the hiccups will become worse and worse, the car would start to stutter at any throttle position above feathering it. if i stop the car, let it cool down fully, its good as new and no problems again.

Already replaced cam sensor, My guess is coil packs on its way out and under full load overheat and cut out intermittently.

Doing LSx coils soon due to this.

 

Is there a proven coil pack replacement?

 

New oem coil pack, quality aftermarket coil pack, or switch to GM LSx coils or Toyota COP's.

I am going the LSx coils route right now, costs about $200 with new acdelco d585 coils from amazon, sadfab mounting bracket, and ebay pigtails.
Still need to order custom magnecor wires as well.

 

I'd like to narrow this down a bit.

 

I've personally been running Fab 9 Tuning's COP conversion on my NB for the past 25-30K miles. No issues in this time, and I've been DD'ing the car for nearly the past 2 years. I however don't have a boosted car, nor is it tracked, so take this with a grain of salt.

Fab9Tuning Plug & Play Coil-On-Plug Conversion Kit - Fab9Tuning

 

Fab9 would be at the bottom of my list of ones to goto. Since you have a MS3 going to LS coils is the best option. There are a few different brackets on the market now to make use of them.

 

I interpreted "quality aftermarket coil pack" as an OEM-style pack NOT from Mazda. I have installed a set of OEM replacements, but would like to have another set on hand in my spare parts box to take to the track, just in case.

 

Their are not any quality aftermarket ones. You either run OEM from Mazda, or upgraded to a better different type of coils.

 

The D585 coils are really very easy and painless. I just did it. I also way overthought it.