87 TR rough idle and stalling/surging

The fuel pumps won't run for very long after cranking if the tachometric relay isn't working. Since you report that it will run more than a few seconds after cranking = your tachometric relay is OK.

 

GREAT NEWS....!!!! Very happy to hear the fix was something minor....excellent Sam.

 

I might have a module that will work. if you want to try it out.

 

I'd like to do some of these checks on my car, but am not exactly sure where things are. If someone verify (or correct me) on the following two things, I'd be grateful:

1) There are two ECU connectors above the passenger side rear wheel well. Those can be taken off with a small phillips head screwdriver and simply pulled out.

2) There is a somewhat triangular piece of metal with a 90 degree bend below the ECU connectors I've identified in 1) above. It looks to be affixed with two bolts. If I remove those bolts I should be able to pull a compartment out that has C12 & C13 connections, as well as protection relay and 10A fuse.

I had mechanic replace one of my ignition coil units (coil, control module, heatsink), and then I replaced the other (passenger side) ignition coil unit. For three days straight in my parking spot, it would start right up and idle between 800-1000. After about 5 minutes, the idle would up to 1200. After about 8-9 minutes of total running, the engine would drop to running on one bank. On the fourth day, I just unplugged/plugged some fuses and wiggled the fuel pump relays (not replacing anything) and the engine ran for 15 minutes perfectly before I shut it off. I just bought and replaced some relays (both fuel pumps and radiator fans), took the car out on the street and it died (drop to running on one bank) within about 10 minutes. Today I let the car idle for about 13-14 minutes, then drove it around parking structure. It died (drop to running on one bank) after about 18 minutes total running time.

 

Not following you here -- no need to remove any screws to unplug any of the 25-pin ECUs (ignition or injection) in the engine bay. There is a metal flap near the end of the connector where the wires leave --- this flap needs to be flexed over which allows that end of the coonector to start to be withdrawn. Then the connector "hinges" in the horizontal plane around a pin on the other end. Once the connector has been rotated open about 60 degrees, the connector end away from the wires (which is hooked shaped) will disengage from the pin that it rotates about. Reconnection is the reversal of that process.

If you are loosing a whole bank, you need to use a timing light to confirm/deny if spark is still present. If spark is there, I'd be suspicious that it's a fuel pump +12V power problem (e.g., burned white connector).

 

OK, I'll take another look at it again given this information. I'm looking at it under commercial parking garage lighting, with a Mag-light as backup, so I'm probably not able to get the clearest of pictures of how everything connects on my own.

Given that I had the major service done in March/April of this year, and I had it back in the shop again for a few months because of this problem, I'm pretty certain that the spark would be there. Something in my guts tells me it's either temperature-related or a fuel pump is going bad. I've read about the fuel pump relay bypass to determine if a fuel pump is good, but I'm not sure what to listen for or look for once I've jumped pin 83 to 87 (or whatever pins I'm supposed to jump to make a direct connection to the fuel pump / power source.

White connectors on the fuse panel look OK to me, but I can't get under the car to check the fuel pump connectors. ....I may to engage the service of my long-time BMW mechanic, who was pretty good at locating electrical issues. Given the relative cheapness of the fuel pumps, I'm wondering if I should just replace them anyways. My car *has* been driven and has just over 50,000 miles.

 

Out of curiousity, what would cause a bank that was firing for several minutes to stop firing?

 

electrical problems

 

Like when an alien spaceship hovers over the car?

 

Can't improve on romano's response of "electrical problems"

If it consistently is OK after cold start-up, fails after a few minutes, and then is OK again after cooling off, I'd be most suspicious of either the power transistor, coil, or ignition ECU failing after heating up some. However, you can deduce some things if you can determine which bank and if it is the coil primary not working or something in the secondary distribution system (for example, the fuel pumps will shut off if the 1-7 primary portion of the 1-7 coil is not working -- so if the engine keeps running on just one bank, that confirms the 1-7 primary stuff is working). You've really got to determine if you have spark on both banks, or not, when it goes to running on one bank to determine if you have a spark problem or a fuel problem (I didn't see anything very conclusive about that in your prior post).

 

as steve says:
check if there is a fuel or an ignition problem.
as I read it all I think it is an ignition problem because the one bank not running happens suddenly. if it would be a fuel problem it would happen within a few seconds

 

then you must be faster than this alien spaceship - remember, it is a ferrari

 

I've been (slowly) doing some more testing.

Seems that it's the right bank that is shutting down. Engine goes to running on one bank and I pull the LH fuel pump relay and the engine dies. Engine goes to running on one bank and I pull the RH fuel pump relay and nothing changes.

I'm trying not to spend money while I'm unemployed, but didn't realize how ridiculously cheap induction timing guns were, so I picked up a well-rated basic one on Amazon for $30 delivered. I drive the car around my parking garage until it goes down to running on one bank and then try and quickly attach the timing gun to the #1 spark plug wire. I've done this twice so far. What I've seen I guess could be construed as a lack of spark? When the engine is running normally, the timing light is strobing very consistently and pretty quickly. In an earlier post, I've mentioned that when the engine goes down to running on one bank, it sounds like it is breathing heavily. When this happens the timing light happens only like once a second - like with each "exhale" of the engine.

What should be my next step?

 

I just came back from dinner and too lazy now to read all again. so I don´t remember all what you have done already.

I would change the ignition module with the coil from left side to right side and otherwise and look if it is still the right side not running or then the left side

 

+1 , and +1 to romano's suggestion -- if it is a problem with something in the coil or power module presently on the 1-6 bank, when you move it to the 7-12 bank, and it fails again, the symptom will be a little different (the 7-12 bank would fail instantly, but then after a few seconds, the fuel pressure on both bank would fall, as both fuel pumps would shut off, so it won't keep running on just the 1-6 bank). If you get there, then you'd swap just the coils, or just the power transistors, to find the bad player.

 

Well, full engine out service back in April, both coils and modules replaced with brand new units in last couple of months. Left and right coil units were not replaced at the same time. Each time a unit was replaced, there was a significant improvement in the way the car ran. What/where are the power transistors?