Spontaneous loss of power/studder

Calling all DSM Gurus and Gods.

This on had me scratching my head for the entire ride from Calgary to Moose Jaw.

The issue is random losses of power/studdering while at cruise. Speed, rpm, and throttle position do not seem to be a factor, but all events took place between 3000-4000 rpm and 110-150kmh.

Basically, I would be cruising along and notice a slight hiccup in the car's power. A little jolt or a studder. For those who have experienced a dying fuel pump, the symptoms are exactly like that. Some times it was only a bit, others the car would studder violently/die when the clutch is depressed.
While this is happening, the AFR is swinging to full lean and remain pegged or jolt up to ~12.0 and then back.
When pressing the throttle, the car would respond normally. Boost would rise, AFR would hit and stay at the right mark, car would accelerate at the normal rate, etc. Therefore, I've ruled out the fuel pump, because it would only get worse if that was the case.

Some times that would fix the problem, other times it would come back shortly after returning to normal cruise.

The AFPR is showing the correct base pressure (42psi) and what I expect it to show when at idle. (~35-38psi)
I've tried removing the ARC2, same issue. I have not however tried going back to stock soils and plugs yet as I'm on a COP setup.

I and leaning towards having put some bad fuel in the car from the pump. Perhaps some water was in there?
The problem was very bad ~150km after filling up and throughout the remainder of that trip. 2 tanks of fuel later, the problem persists but is not as frequent or violent.

So... Thoughts?

Attached are 2 logs of the car experiencing this problem. One labelled "230", the issue is at 230s.

https://drive.google.com/file/d/0B9XB0-BqtNV7RVo0WnZadWYyNVk/view?usp=sharing

https://drive.google.com/file/d/0B9XB0-BqtNV7YmpmSG9XN3piZjQ/view?usp=sharing

Did you run into any snow or rain on the road while this was happening? Environmental factors could point to an electrical / ignition problem.

Did you have any electrical issues such as dash lights flickering or the radio turning on and off? I'm thinking along the lines of an ECU or MPI relay issue.

Sorry I can't take a look at the logs right now but I figured I'd get the brainstorming going.

Nothing that the car hasn't experienced before. Snow is normal, and no rain recently.
The car is receiving > 14V from the alternator and there has been no indication of any electrical interruption from inside the car.

I thought about the MPI relay, but I don't think it would return to normal when putting the car under additional load. I kind of ruled that one out.
I haven't completely ruled out the ECU yet, but at the same time, I don't have any reason to suspect it.

Are you running a stock o2 sensor or relying on wideband?

Water is heavier than gasoline so it may very well be. Water could be stabilizing near the pump during steady cruise conditions and moving away from the pump under boost conditions. If water is really in gasoline than it should also show the signs when parked and idling on the flat ground. This never happen to me so it's hard to be sure if this is really it.

You can drain your tank by redirecting return line into a gasoline canister.


Will the loss of spark send AFR into lean? logically it should not (should be oposite) but anyone correct me if i'm wrong

Yes I believe a misfire or complete lack of spark on a cylinder can show up as lean on a wideband, the raw fuel is travelling past the sensor but so is all the unburned oxygen.

How about the airflow signal dropping out? What are you running there?

I'm running narrowing Sim off of the Wb.

When thus issue was at its worse, I had trouble idling. Tue car just died sitting at a light a couple times.

Hmmm. Thinking about it, unburnt fuel should show up as rich, no? So if it was an actual misfire, it would show as a rich spike? Or do I have that backwards??
Then again, less O2 from the lack of combustion.... Now I'm all backwards....

Ill check what you're looking at there Rob. What log?

I didn't see the logs, just a hunch from what you're describing. I've had similar issues with a wet MAFS or a loose connection.

Looking at both of the logs, the airflow signal seems to rise and fall as it should.

Maybe your wideband is wearing out. Mine was doing that... But I also got a code e8 eventally and had to restart the car. I replaced the sensor.. Never did it again. Member.... They have an extremely shortnlife spand. Im switching to stock o2 his year. Switched the 1g to stock o2 sensor last year, ran way smoother.

The oxygen sensor doesn't care about the fuel in the exhaust, it cares about the amount of oxygen in the exhaust (hence the name). A misfire will let more oxygen into the exhaust stream than a normal combustion cycle and the sensor will pick that up as a lean reading.

That's my thinking, I've seen this kind of behaviour when I was dealing with a miss at idle.

I am not convinced that's it either, assuming you have the mtx-l the sensor that comes with it is the upgraded one which can easily handle being in the stock location.

I'm yet to have an O2 sensor wear out. This one seems to be behaving normally when in closed loop. I'll do a rag test on it soon. It's also installed in the stock location.
They wouldn't put a sensor there if it couldn't handle the heat.

I'll be leaving the car for a week so I'll have to put this on hold.
Still hoping it was just some bad fuel.

are all your heat shields in place?

The sensor is already in pretty much the hottest place aside from the cylinders themselves - having heat shields on is only going to make it hotter as it will keep the heat trapped in more. (i.e. it really shouldn't matter if heat shield or not unless his wires are somewhere they shouldn't be)

But they do go bad. And stock location is often blamed. Stock o2 sensors are not the same as widebnd sensors. You said the issue happenes during cruise.... Is that not closed loop??? Then when you said you give it throttle, it accelerates fine. Which would mean that it runs better in open loop, when its ignoring the o2 sensor.

Il still say its the wideband.

Whoops, reversed those 2. (Closed and Open)

Fair enough. I'll agree that it's freakin hot right there and that the sensor can wear out.

I'll test the sensor as soon as I'm back with the car. Should be on the 14th.

Except that modern cars all have wideband O2 sensors as close to the exhaust as the stock location on a DSM so it's not really a major issue. Of course the manufacturers are going to say 'use this close at your own risk' but realistically there shouldn't be a significant decrease in sensor life at the stock O2 housing location.

That's not to say Johnny's sensor isn't bad and if it is that heat didn't cause it, but I do know Johnny ran leaded fuel a bunch in that car many times when he worked at the airport and that IS something would greatly affect O2 sensor life.

I am at work and cant open the logs, but out of curiosity, what did your voltage look like? My car did some odd things like this when the voltage regulator in the alternator was failing.

This could be true, but I don't feel like the sensor would start behaving again after going WOT if it was wearing out. Also, the sensor looks to be in the same shape as the one in the Spyder which has never seen leaded fuel. "Looks" being the key word. haha

Well, thats what I get for skimming the posts haha.

My next thought would go right to the COP system. I remember reading posts a long time back of someone having similar issues during long drives with their COP system. I cant find the thread, but I remember them stating that putting factory ignition components back in cured the problem.

Not that I necessarily think it's the case, just something to keep in mind



I believe this was Johnny as well? Hahaha

My car did exaclty what your saying.. Ran fine and smooth during full throttle.. Then start acting up again when cruising. I drove for a week or so like this untill it started giving me codes. I swapped the sensor, ran much better.

I was told that the mtx gauge/controller may also be the culprit and yes, would run better with a fresh calibrated sensor. After a lot of research tho.. I actually opted to switching widebands for this year. Too many issues with the mtx.

Standby for an update. I will be driving the car again in a week or so.

I did think about switching back to the OEM ignition setup, but didn't quite get there.

I'll also do a fuel rag test on the O2 sensor.

Can you run a stock o2 sensor? It sounds intermittent.. The fuel rag may not work.

Because I suck at updating these things....
Replaces the WB O2 sensor and the problem ceased to exist.

I suppose the sensor would error on the rich side and cut fuel. That would also explain why when the ECU entered open loop.

Problem solved. Boostin the summer days away!