Constant throttle stumble.

[irdave]

Ok 'migos.  I'm at a loss and Jim is getting tired of dealing with my issues.

 

My car has a bunch of weird crap, but I'm to the point that I don't think it's the weird crap that's causing my problem- because I've checked and changed about everything having to do with the weird crap.  So I'm wondering if it's not something simple, like a leaky exhaust gasket...  I need your help.

 

Here's what I got; I have a stumble, a miss.  I can feel it at idle, can feel it at most constant rpm situations.  (Haven't tried it at higher than maybe 4k rpm, just because.)  It either goes away or becomes unnoticeable while on moderate to big acceleration.  It's less noticeable or not there right after getting started for a couple minutes.  And I didn't notice it very much running down the freeway today, which was interesting.  Technically this started right after the COP swap from the stock dizzy, which made me chase all the COP stuff, but I don't think that's it for a lot of testing reasons- like it runs fine on Jim's car.  I haven't tried reinstalling the dizzy yet, although it's sitting on the bench waiting.

 

I rectified a bunch of little things trying to sort this, which is good, but still.  So I've looked for vacuum leaks, and fixed a couple good ones, on the intake side.  (I'm running alpha-N, so there really isn't any metering device per se.)  So plan is to install all the new Speedhut gauges and see if that somehow magically fixes whatever the hell is going on.  Also going to look the exhaust side over closely for leaks.  But what other things cause a constant rpm stumble?  Bad timing?  Bad o2 mixture?  I haven't checked compression / leak down yet because it starts on all 4 and pulls pretty good up top.

 

s14, haltech, coil on plug, carbon intake, stock engine, on gasoline with very infrequent ethanol mix- maybe 3 times in 2 years.  The haltech has the ability to log a lot of what's going on.

 

Please, shoot from the hip.  What kind of stupid things have you seen.  I've been dealing with this since June.  It's driving me crazy.  Like, there's a z3m coupe on BAT.  I bet it runs just fine.

[tech71]

Well, I was going to say plug wires but I guess not.

My X5 developed an annoying intermittent stumble along with a check engine light. It was a failing coil.

But sounds like your set up would know that and tell you along with which cylinder, out of my league.

[ray_]

Can you narrow it down to a specific cylinder?

 

Have a look at your brake booster vacuum, but I don't really think that's it.

 

You're running closed-loop, right?

 

Change all the spark plugs....

 

I assume your engine management hardware is wired direct from the battery and thru relays.... check the grounds there too,

 

GL,

[tzei]

Do leak down test! It can start & run just ”fine” but all it could mean that you have about same amount leak in all cylinders. 

[irdave]

9 hours ago, ray_ said:

Can you narrow it down to a specific cylinder?

 

Have a look at your brake booster vacuum, but I don't really think that's it.

 

You're running closed-loop, right?

 

Change all the spark plugs....

 

I assume your engine management hardware is wired direct from the battery and thru relays.... check the grounds there too,

 

GL,

 

I can't; I hooked Tom's timing light up to each wire and they're all reading about the same rpm...

 

I looked at the brake vacuum, no apparent leaks.

 

Closed loop, so the ECU seems to be adding fuel where the stumble is, because the ECU is seeing too much o2 from the o2 sensor in the exhaust.

 

Changed the plugs.

 

Big e30 cable to the front, then wired from there.  ECU ground is to chassis; tried it directly around the side of car for test- no difference.

[irdave]

6 hours ago, tzei said:

Do leak down test! It can start & run just ”fine” but all it could mean that you have about same amount leak in all cylinders. 

 

Damn you! ?

 

Ok, I will.  What keeps catching me is that it ran with no problems with the distributor and I have problems directly after the COP swap.  So not saying it's not the engine, but it's been low on the list.  But I suppose we're getting pretty far down on the list- so it's closer to the top now.

 

Trying to look on 'bright' side; winter is coming.  How much can you bore an s14?  Maybe add some compression?  I'm at altitude and have the ability for knock sensor...

[irdave]

11 hours ago, tech71 said:

Well, I was going to say plug wires but I guess not.

My X5 developed an annoying intermittent stumble along with a check engine light. It was a failing coil.

But sounds like your set up would know that and tell you along with which cylinder, out of my league.

 

Yeah, they were new plug wires.  I bought the sub harness from fleabay- same one Jim is using.  I've gone over it 2 or 3 times trying to find something.  Going to get my wife to help me look at resistance along the entire wire from ECU to plug on harness just to see if one of them is holding on with one strand.

 

And going to look and see if the ECU can look at individual spark and fueling.

 

But I've been on the phone with Haltech for a fair bit of time- I don't think this is an ECU issue, I think this is a basic mechanical / electrical issue...

[zinz]

Hall sensor at the trigger wheel?

[jimk]

Not difficult to give a try.  Run a manual disconnect wire from battery power direct to the B11 ECU power in or alternately to the switched power into the rely box  The ignition switch may have intermittent power that is not noticed when you have your foot in it.

 

Do you still have to turn your heater fan on to get the engine to shut down? 

Edited October 2, 2021 by jimk

[John76]

Did you look at the shielding on the harnesses to the ECU and coils, etc.?

Anything that causes interference with those low voltage signals can cause weird things to happen.

Could be as simple as a poor alternator ground.

Watts of luck!

[Lorin]

Timing can cause an otherwise unexplained misfire and remember a misfire almost always reads as lean on a wideband 02 even though it could already be rich. 

[irdave]

2 hours ago, John76 said:

Did you look at the shielding on the harnesses to the ECU and coils, etc.?

Anything that causes interference with those low voltage signals can cause weird things to happen.

Could be as simple as a poor alternator ground.

Watts of luck!

 

I was so hoping to see one of your wiring diagrams for my car. 

 

And it's not the alternator ground, nor either of the other 2 grounds from the engine to the chassis- based on your suggestion I cleaned them all just now- didn't change anything.  But man! do those ITBs sound good with no intake!

3 hours ago, jimk said:

Not difficult to give a try.  Run a manual disconnect wire from battery power direct to the B11 ECU power in or alternately to the switched power into the rely box  The ignition switch may have intermittent power that is not noticed when you have your foot in it.

 

Do you still have to turn your heater fan on to get the engine to shut down? 

 

I still have to turn the fan on to shut the car down, but if I unplug the dash it works as it should, as it did with your ECU, which is why it was pretty low on the list.  But as I said above...

 

I'll try to directly power the ECU around the ignition now.  Maybe just unplug it from the connection at the ignition switch and run that directly to +12v.

[ray_]

2 hours ago, irdave said:

 

I was so hoping to see one of your wiring diagrams for my car. 

 

And it's not the alternator ground, nor either of the other 2 grounds from the engine to the chassis- based on your suggestion I cleaned them all just now- didn't change anything.  But man! do those ITBs sound good with no intake!

 

I still have to turn the fan on to shut the car down, but if I unplug the dash it works as it should, as it did with your ECU, which is why it was pretty low on the list.  But as I said above...

 

I'll try to directly power the ECU around the ignition now.  Maybe just unplug it from the connection at the ignition switch and run that directly to +12v.

You... WHAT? ?

 

Ensure all your engine management grounds are to the same central point. I mean it may be a ground loop issue.

[SydneyTii]

I’d reinstall the distributor just to start from a known base, see if it goes away and move forward from there?

[jimk]

4 hours ago, irdave said:

Maybe just unplug it from the connection at the ignition switch and run that directly to +12v.

There ya go.