OBD1 S52 Dr Jekyll Mr Hyde

[hammslice]

I have an OBD1 S52 that's has been acting strange. Above 3500 RPM it runs consistently strong and as expected. Below however, it somewhat erratically runs like its missing one or two cylinders. Down on power, distinctly different exhaust note. If I stay on the throttle when it does this, as soon as it passes 3500, it wakes up and acts normal.

In trying to troubleshoot this, I have checked most of the sensors under the manifold. Throttle posi and intake air temp checked out. DME coolant did not and knock sensors were looking shabby so I replaced those three. I also used some MAF cleaner on the MAF and cleaned the throttle body. No change.

Is there something in the DME logic that changes at 3500?

97 S52 100k mi before swap, less than 3k since (I did not always behave like this.)
Racers market OBD1 for 93 octane, 3.5" euro maf, 24lb injectors, LTW flywheel idle bump.

Anyone else experience this before? Tips on where to look next? I'm stumped.

Thanks in advance R3vers, I believe in you!

[NotJesus]

Vanos

[hammslice]

Vanos

I thought there was a CEL code for vanos?

[M3PO]

I had a similar issue and everything I read seemed to suggest that VANOS issues are not as pronounced as what you are describing.

There is a code for VANOS. Unplug the solenoid and take the car for a spin.

[squidmaster]

really sounds like vanos issues. you may not end up seeing a code for it. you can always reset your ecu (disconnect battery, hit brakes a few times, let it sit for a few minutes, reconnect) and see if that changes anything, or maybe triggers the cel to come on.

[Zesty Bonanza]

"V-tec just kicked in, yo!"

[hammslice]

"V-tec just kicked in, yo!"

Basically, Haha.

Anyway, got a new VANOS solenoid. No change. Drove with the solenoid disconnected as well. The low rpm behavior was the same but the high rpm was slightly down on power. Correct smooth exhaust note but different pull than with it connected. This leads me to believe that VANOS is not the issue. (Anybody need a solenoid?!)

Got CELs 1271, 1274. And 1215. Ign Coil #1, Ign. Coil #4, and MAF. Used some MAF cleaner and that didn't keep the code away. Switched coils 1/2 and 4/5 hoping to see the code move to those cylinders. strangely they did not. I came across a thread about hairline cracks in the underside of the packs causing this behavior. Examination of all 6 showed what I would consider the start of a crack on almost all of them. So they are all bad or none of them are bad...

Something wrong in the connections or in the harness somewhere? Any other ideas?

In researching buying new cool packs I came across something confusing. From what I see there are 3 types out there. OBD 1 Bosch, OBD 1 Bremi, and OBD2 Bremi. Based on the pictures on sites like ecs, turner, bavauto, the OBD1 types are square, and the OBD2 are round. This is consuming because the packs that came on my motor before I converted it to OBD1 were Bosch and square. A buddy of mine used to have an S52 MCoupe and he was pretty sure his were square too. I will just base my order on the part number but I was curious if anyone had any light to shed on that apparent mismatch.

[M3PO]

I've had two sets of OBD1 Bosch coils with cracks. The car ran fine on one set, and on the other it ran like shit at high RPM. All coils Ohm'ed out correctly.

The round coils are not what you need. There are OBD1 Bosch, OBD1 Bremi, and OBD2 coils (not sure which brands). The OBD2 coils are slightly different (but again, not round).

Basically, Haha.

Anyway, got a new VANOS solenoid. No change. Drove with the solenoid disconnected as well. The low rpm behavior was the same but the high rpm was slightly down on power. Correct smooth exhaust note but different pull than with it connected. This leads me to believe that VANOS is not the issue. (Anybody need a solenoid?!)

Got CELs 1271, 1274. And 1215. Ign Coil #1, Ign. Coil #4, and MAF. Used some MAF cleaner and that didn't keep the code away. Switched coils 1/2 and 4/5 hoping to see the code move to those cylinders. strangely they did not. I came across a thread about hairline cracks in the underside of the packs causing this behavior. Examination of all 6 showed what I would consider the start of a crack on almost all of them. So they are all bad or none of them are bad...

Something wrong in the connections or in the harness somewhere? Any other ideas?

In researching buying new cool packs I came across something confusing. From what I see there are 3 types out there. OBD 1 Bosch, OBD 1 Bremi, and OBD2 Bremi. Based on the pictures on sites like ecs, turner, bavauto, the OBD1 types are square, and the OBD2 are round. This is consuming because the packs that came on my motor before I converted it to OBD1 were Bosch and square. A buddy of mine used to have an S52 MCoupe and he was pretty sure his were square too. I will just base my order on the part number but I was curious if anyone had any light to shed on that apparent mismatch.

[328ijunkie]

OBD2 coils dont fit in OBD1 valve covers for shit and vise versa.

There were both OBD1 bosch and bremi coils. A general rule of thumb is OBD2 coils have 2 bolt holes, OBD1 ones have 4.

[hammslice]

Fresh plugs made zero difference.

Drove with the MAF disconnected. Character was slightly different and the effect seemed marginally less pronounced but it was still there. Point is, my MAF may be on its way out but I don't believe it is causing the crappy running between 2k & 3.5k.

[squidmaster]

Can you borrow a MAF from a friend? Hit up a JY and pick up a maf for a couple bucks to see if it makes any difference.

[pandaboo911]

OBD1 S52 Dr Jekyll Mr Hyde

Could be a loose crank sensor vibrating at 3k?
Could be too much fuel pressure causing that too, effect would be less noticeable at WOT. Could be a sticky VANOS fucking with the timing. As mentioned you wouldn't get a code for this.

We're your old plugs black / covered in soot?

You may have to remove the VANOS and replace the teflon seal in there. Do the bearing too while in there, it's super easy. Just borrow the cam blocks from somebody.

Does the car still do it while sitting still? Iirc the VANOS doesn't modify timing unless you have a speed signal so if it doesn't happen while you're parked in neutral it'll be the VANOS.

[hammslice]

Could be a loose crank sensor vibrating at 3k?
Could be too much fuel pressure causing that too, effect would be less noticeable at WOT. Could be a sticky VANOS fucking with the timing. As mentioned you wouldn't get a code for this.

The effect is definitely there at WOT. I'm using the m42 crank sensor in the rearward location so it's a little tough to get to but I will check this next time I'm at the car. Recently changed the knock sensors and I can't remember if I checked that one while I was in there or not.

We're your old plugs black / covered in soot?

Plugs were not black. See attachment. 6, 5, 4, 3, 2, 1.

Does the car still do it while sitting still? Iirc the VANOS doesn't modify timing unless you have a speed signal so if it doesn't happen while you're parked in neutral it'll be the VANOS.

I think it does but I'm not sure. I feel like I have revved it and it spit just in the driveway but I wasn't specifically looking for it to at the time. Will check next time.

Thanks for the suggestions!

[hammslice]

Also, here are the coil packs. 3, 2, 1.

[hammslice]

And 6, 5 , 4.