This week's e36 diagnostics challenge

BMW e36 318ti (m42). A couple of weeks ago the coil pack went south shooting extra juice through the brain box (DME) - visible roasting of one of the copper traces on the board. So coil pack, plugs/wires and brain box and I'm back on the road. Noticed that at higher revs it's acting like it's bouncing off a rev limiter (varies, but can happen between 4700 rpm and 5500). Runs/drives perfectly normal below 4700. BMW red line is around 6500. Has a Dinan chip that supposedly eliminates the rev limit . So what might I be looking at? I would have thought if the chip got toasted it would be a work/no work thing not setting arbitrary rev limits or otherwise rewriting the chip's code? My other thought is fuel starvation, but would have thought it wouldn't be a sudden bounce at a given rpm - more of a tailing off of power. What else - faulty new coil pack? Fuel filter, fuel pump? I have a spare factory chip (but may have to spend some money at a dealer to sync the alarm system to it - the Dinan chip bypasses the alarm sync thing, so not looking forward to plugging in the factory chip .

thoughts from the GRM brain trust?

cutting out at high rpms? sounds like the coilpack

Agreed . . .

I was thinking ecu relearn, but there was no mention of idle and on throttle sputtering or hesitation.

How does it drive at low rpms, high load like lugging up a hill??

Do you have any scan tool abilities??

Is it just rev limited? or is it cutting out a specific speed as well?

Coil pack.......could be a toasty wire in the harness to that cylinder on the coil brick.

It is a coil pack - and what usually kills BMW coil packs is oil leaking into the plug well from a bad valve cover gasket or overzealous engine cleaners with pressure washers filling same with water.

The 318 uses a single coil brick mounted to the strut tower, so oil/water would only short the plug wires. Speaking of which, how are the wires? I replace the plug wires a lot more often than coils on those motors. You could try spraying water on the wires while the car is running to find any shorts.

Cone_Junky wrote: The 318 uses a single coil brick mounted to the strut tower, so oil/water would only short the plug wires. Speaking of which, how are the wires? I replace the plug wires a lot more often than coils on those motors. You could try spraying water on the wires while the car is running to find any shorts.

DOH, you are right... I should pay more attention .... M42, I was picturing the COP setup off the M50 motor but... same thing does apply - you can still short them out with oil by drowning the plug and shorting the wire in the hole - which will kill the coil pack.

Giant Purple Snorklewacker wrote:

Cone_Junky wrote: The 318 uses a single coil brick mounted to the strut tower, so oil/water would only short the plug wires. Speaking of which, how are the wires? I replace the plug wires a lot more often than coils on those motors. You could try spraying water on the wires while the car is running to find any shorts.

same thing does apply - you can still short them out with oil by drowning the plug and shorting the wire in the hole - which will kill the coil pack.

+1 That brick can still go bad.

Hmmm - brand new coil pack (aftermarket not oem) - but that is a "what changed" factor. New plugs, plug wells were dry. When the old coil pack failed it put quite a bit of juice back to the DME - enough heat to melt a layer of plastic covering a trace - but it only failed on #3 cylinder - still ran (on 3 cylinders) with toasted DME and bad pack. I looked over the harness wires - no visible signs of insulation melting. Currently running on all 4 - drives normal - no noticeable loss of power until the upper revs - where it is a sudden cut and acting like a rev limiter bounce. I'll check fuel pressure, but agree it sounds more like a spark issue.

If a power surge came back through the harness with enough amperage to visibly damage the pcb, chances are the harness or at the very least, the harness connector pins are also damaged. I can't explain how exactly that damage would cause the symtoms that you are experiencing, but you should go back and carefully check all the individual connector contact surfaces on both ends of the harness.

I had a spark cut out issue on my M44 318ti. Initially it was happening at seemingly random engine speeds. Shortly after it got to the point where it had a 2000 rpm limit. Would run fine under 2k, but would not rev above. It threw a cam position sensor code. I replaced it with an aftermarket one with out any change. Next I swapped the cam and crank sensors for good, used OEM ones. That solved the issue. Temporary loss of engine speed signal might also cause your issues.

JMcD wrote: I replaced it with an aftermarket one with out any change. Next I swapped the cam and crank sensors for good, used OEM ones. That solved the issue. Temporary loss of engine speed signal might also cause your issues.

I've got a similar issue on my M42-powered E30 (self-imposed rev limit at 5800), and that's the second time I've seen the crank position sensor be pointed out as the culprit. I haven't done anything about mine since it hasn't gotten worse, but just throwing that out there.

unevolved wrote:

JMcD wrote: I replaced it with an aftermarket one with out any change. Next I swapped the cam and crank sensors for good, used OEM ones. That solved the issue. Temporary loss of engine speed signal might also cause your issues.

I've got a similar issue on my M42-powered E30 (self-imposed rev limit at 5800), and that's the second time I've seen the crank position sensor be pointed out as the culprit. I haven't done anything about mine since it hasn't gotten worse, but just throwing that out there.

Up top like that can also be the speed sensor in the rear diff - E36 models starting with the Bosch 413 ECU had a variable rev limiter which was imposed for 1 & 2 (solved by engine RPM vs diff RPM) but if the sensor is bad - it always thinks you are in 1st gear and clips you at the lowest setting.

It is a clean dump out though because it cuts timing and fuel - if you have a rough edge, bogging or struggling to gain RPM across all cylinders it likely is a cam angle, crank pos or possibly a filthy/bad MAF. If the crank pos goes altogether the car won't start at all.

Dropping a single hole is always a plug, wire, coil pack problem when it isn't a bent valve or head gasket.

One other long shot - my race car had a high RPM ragged coil-pack like issue that turned out to be a failed alternator that stopped producing power at high RPM and left me running everything off a super lightweight Braille battery. After 15 minutes voltage would drop and it would progressively get worse. Since it charges at low RPM, the battery would always be fine when I got to the paddock so I never suspected it. It took me 2 sets of coils, rigging a fuel pressure gauge so I could see it on track, several beers and finally a volt meter taped to the roll cage to sort that one out.

Giant Purple Snorklewacker wrote: Up top like that can also be the speed sensor in the rear diff - E36 models starting with the Bosch 413 ECU had a variable rev limiter which was imposed for 1 & 2 (solved by engine RPM vs diff RPM) but if the sensor is bad - it always thinks you are in 1st gear and clips.

Please tell me that using a e30 engine harness in an e36 negates that.....

yamaha wrote:

Giant Purple Snorklewacker wrote: Up top like that can also be the speed sensor in the rear diff - E36 models starting with the Bosch 413 ECU had a variable rev limiter which was imposed for 1 & 2 (solved by engine RPM vs diff RPM) but if the sensor is bad - it always thinks you are in 1st gear and clips.

Please tell me that using a e30 engine harness in an e36 negates that.....

Not if you use a 413 DME. If you use the E36 ECU you need a chip programmed to ignore it.

I have a 282 dme - it's a mid-level some of the 96 year upgrades/changes, but not all of them. Also understand a purple label m42 dme will work on any. There's some hacks for the ewsI system - not so much for the ewsII alarms/immobilizer.

Giant Purple Snorklewacker wrote:

yamaha wrote:

Giant Purple Snorklewacker wrote: Up top like that can also be the speed sensor in the rear diff - E36 models starting with the Bosch 413 ECU had a variable rev limiter which was imposed for 1 & 2 (solved by engine RPM vs diff RPM) but if the sensor is bad - it always thinks you are in 1st gear and clips.

Please tell me that using a e30 engine harness in an e36 negates that.....

Not if you use a 413 DME. If you use the E36 ECU you need a chip programmed to ignore it.

Let me rephrase, e30 engine harness, e30 dme, e30 engine but in an e36.....I'll have to look at the ecu # I got from oldtin.

More weirdness - running normal at the top of the rev range tonight. Hate the intermittent stuff, but maybe a clue on inspecting the harness very closely.

In reply to oldtin:

She's angry at you for something.

Yeah, making her a commuter car through a Chicago winter - salt. They say the salinity of Lake Michigan is changing due to the runoff. Saw an e46 today full of rust holes

In reply to oldtin:

My road has been salted once this year, sanded twice though. Yay BFE Indiana.

yamaha wrote: Let me rephrase, e30 engine harness, e30 dme, e30 engine but in an e36.....I'll have to look at the ecu # I got from oldtin.

I've never heard of anyone doing a backward swap E30 powah into an E36... but, no, does not matter. The E30 and it's bits care not.

My wiring harness was hacked up..... And didn't feel like dealing with the EWS2 E36 M3 that it shouldn't of had.