Engine Coughs sputters, jerks, hiccups.. whatever you want to call it

[Gruntc1]

So my long struggle with this beemer has finally come to M42 club... a couple of new parts that I've put too much money into and i need help. I've Redone vacuum lines and got rid of the mess under the intake, brand spanking new idle control valve, new throttle position, new crank position. New fuel pump and pressure regulator (no new relay). ANYWAY my problem is that if you stop it to the floor it will cough snap and sputter and never really pick up, it's hard to even ease into it and it wants to die and even when you can get the rpm's up, there's not enough power like it should have.
I plugged a timing light in to make sure that i was getting even consistent signal from each cylinder, and when you point it down at the main crank you can see that the timing seems to be advancing correctly and all that crap. when it sputters i can tell that its not an ignition issue. Vacuum lines are all brand new and tidy and there is plenty of fuel in the fuel rail, my thought is, is it getting too much fuel? and if so how the hell do i fix it? one thing i know is that when i unplug the MAF it goes to a 1000 rpm map setting, but when you ease into the throttle it does the same thing... don't know what this means really but there you go. Also the only code I get is a speed sensor (1234) and its the wheel speed sensor on the differential at least i am pretty sure. but please help me I'm beginning to get really frustrated after everything I've done, and i have owned it while it worked properly it was a craigslist deal that I drove about 120 miles back home... NEED IDEAS

[DesktopDave]

I'd do a pressure test on the fuel lines, and see if the injectors are all gunked up.  The speed sensor might require some work.  If your speedo is intermittent I'd check the pins on the diff plug and associated wiring.  If not, it's likely that the speedo output to the DME is at fault.  I'm not sure how I'd fix that, maybe by popping in a new cluster board?

How are you sure it's not a timing issue?  There are a few high-mileage ECU's I've seen that burned out a coil driver.  Maybe yours is on the way out?

[Gruntc1]

Thanks so much for the reply, as far as the speed sensor goes, i re-soldered my whole dashboard cluster and it fixed my fidgety speedo and I thought that i fixed the problem. However i got the speed sensor code a couple weeks later. When you say pop in a new cluster board you mean the "si board" right?

As far as timing goes its nothing more than a visual check for consistency. since you cant properly check it like an old carbuerated vehicle, i put the timing light on each cylinder and at idle it is normal without any breaks when it stutters, and when the light is pointed down at the harmonic balancer (i think that's the name, where the crank pos. is) you can see the affects of the altered timing produced by the DME to adjust the timing curve, and it produces the same results on all 4 wires. However this is the wires not actual plugs but i feel my problem is beyond plugs. but you never know.

Back to the "si" board if you will, if that would be the problem would it have to be exactly for my car im assuming? or did some of the e36's use the same board?

Also am i wrong in thinking that the speedometer to DME and the rear Diff to the cluster would be separate codes? or did that come with more advanced computers I've heard of speed sensor 1 and 2 and im not sure if there are more than one code that would be given.

For the Coil driver issue what would be more symptoms and solution to the problem, a new ECU? Thanks again for your reply

[bmwman91]

Double post deleted.

It is fairly unusual to have ignition system problems on these cars. Being totally solid-state, it is quite robust. It is not unheard of to have coil drivers crap out, but it is rare. Occasionally one of the coils dies, too.

I would be checking over the fuel system more completely. Start with basic stuff like an old fuel filter. At low flow rates, you could still see the right pressure at the fuel rail with a plugged filter. The pump itself may be dying, or the fuel pressure regulator may be working improperly (unusual, but possible). Can you have a partner operate the gas (in neutral) and try to rev it while you sniff the exhaust? Does it smell particularly rich?

Four times out of 5 these issues are fuel related.

[DesktopDave]

Thanks so much for the reply, as far as the speed sensor goes, i re-soldered my whole dashboard cluster and it fixed my fidgety speedo and I thought that i fixed the problem. However i got the speed sensor code a couple weeks later. When you say pop in a new cluster board you mean the "si board" right?

Nope - I meant the drive board that the gauges plug in to.  A weak cap or damaged resistor might cause an issue with the signal output to the DME.  The diff sender inputs a signal that's amplified and re-distributed to the DME (and cruise control if installed).

As far as timing goes its nothing more than a visual check for consistency. since you cant properly check it like an old carbuerated vehicle, i put the timing light on each cylinder and at idle it is normal without any breaks when it stutters, and when the light is pointed down at the harmonic balancer (i think that's the name, where the crank pos. is) you can see the affects of the altered timing produced by the DME to adjust the timing curve, and it produces the same results on all 4 wires. However this is the wires not actual plugs but i feel my problem is beyond plugs. but you never know.

Back to the "si" board if you will, if that would be the problem would it have to be exactly for my car im assuming? or did some of the e36's use the same board?

I was assuming that you had an e30 based on your sig...I've never had an E36, but I can't think it'd be that much different.  BMW tends to be very evolutionary as far as new models go.    it's good to go with your gut sometimes but I'd urge you to test a few components out to isolate the problem.  Bosch compensates for a lot of related variables - TPS, O2 reading, RPM, intake temp, coolant temp, car speed, etc when picking spark & fuel maps.  Even intake vacuum is a variable as it directly effects the fuel pressure at the rail.  IMHO I'd be eliminating those variables as causes before replacing more parts.  Get a DMM on the coolant and air temp sensors...get a pressure reading on your fuel pump.  A plugged filter or weak pump will let the car idle perfectly but sputter in high-load situations as fuel demand goes up.

Also am i wrong in thinking that the speedometer to DME and the rear Diff to the cluster would be separate codes? or did that come with more advanced computers I've heard of speed sensor 1 and 2 and im not sure if there are more than one code that would be given.

I'd assume they're the same code.  The DME isn't all that smart, just noting a failure. We're talking late 70's tech more or less...my 633CSi (build date 11/1981) had a very similar DME.

For the Coil driver issue what would be more symptoms and solution to the problem, a new ECU? Thanks again for your reply

Yep - or de-solder and replace the offending coil driver.  It's unlikely but possible.  If the car is idling well, I'd put that near the bottom of my troubleshooting list.   Sensor failure or fuel pressure troubles would be first on my list.

[///m42 sport]

i know when I had problems similar, it was ignition coil related

[kingsalmon]

I would replace the spark plugs 1st as they are pretty cheap.  Always go cheapest to most expensive when diagnosing.  Check the spark plug wires as well.  I've heard they tend to fail around 150k.  I am currently working through a similar problem.  I've replaced the spark plugs, fuel filter, and fuel pressure regulator.  These parts have helped.  I'm going to install a COP system next, since it isn't that much more expensive than the plugs themselves.  I'll let you know what happens.

[kingsalmon]

COP kit fixed the problem.  All hesitation on acceleration is gone!  Seems a bit more responsive as well.  I would say that the wires or the coil pack was the culprit.