E30 M20 C191 Plug Replacement

The C191 plug connects the fuel injector harness to the rest of the electrical system. A bad C191 plug can lead to all sorts of problems –

  • hard starting
  • rough idle
  • lack of power
  • fault codes for fuel injectors or temp sensor

The location of the C191 plug makes it susceptible to water. Check out the corrosion on my plugs:

The connectors are not available separately from BMW. You have to buy a new fuel injector harness or engine harness. But why replace one defect with another? So that’s why a lot of E30 fixers have went aftermarket. I chose a motorsport/military spec Deutsch DT connector. I really should have read up on this during my engine build and it would have saved a lot of headache later on.

Do not hardwire the harnesses together. Although it may be tempting as an easy fix, there are major drawbacks to it. They should be separated so the harness can be removed during manifold or cylinder head service.

Replacing the connectors means cutting them off, exposing the wires, crimping pins to the ends, and inserting them into the Deutsch connector. There’s no easy way to do this with the harness on the car but removing it is very difficult too (and is only half of the harness).

The Deutsch connector is not for the weak. First, the connector set that I ordered from Amazon came with no instructions or diagram (no surprise). Videos and online descriptions were no help. The pins crimp differently than the usual crimp connectors. My multipurpose crimp tool did not work well and I settled for ordinary needle-nose pliers. Access and room to work is terrible. Once the wires are crimped they have to be pushed through the rubber seal and then locked down in the connector.

Here’s where a diagram would have come in handy: I didn’t know which pin went where. I wrongly assumed the male pins went in the male connector. After getting all 12 pins in place I realized it was the other way around and the pins weren’t making contact inside. Doh! Live and learn.

The male pins fit in the larger female housing and get locked in with the green wedgelock. The female receptacles fit in the male connector and should be flush with the housing (or just below the surface of the orange wedgelock once installed). I had to carefully pull them all out and run them through the opposite connector. Once that was done, probing with my volt meter confirmed the injector power line had 12.5v with the key on. I also probed the pin on the DME connector and the coolant temp sensor and both had the same resistance. So my little wiring project should be a success!

So why are the injectors not spraying and the engine still not starting?

To read more on this situation, see my M20 starter post by clicking here.

Click here for my C191 connector photos.

E30 M20 C191 Plug Replacement

E30 M20 Starter Problems

My 323 did not start a month or so ago. I turned the key but there was no response from the starter. I had strong lights on the dash and 12v on my battery gauge so I didn’t suspect a weak battery. I was able to roll and bump start the engine.

After that there were no issues for a few weeks until it happened again. Because it was intermittent, and I have other key issues, I first suspected that the ignition switch was failing. The switch is no longer available from BMW. And I think the current ignition switch is from an E30, which is NLA too. I looked into a keyless push-button start system but did not commit to buying one. Then the car acted normally for another few weeks.

In the meantime I did a lot of research. One possibility was the engine electrical grounds. I re-used all of the E21 grounds so I’m not missing any. It’s possible it could use more but given the intermittent behavior I mostly ruled this out. That left the starter and starter solenoid itself.

One helpful feature in older BMWs is the ability to bypass the key and activate the starter from the diagnostic port. By jumping pins 11 and 14 you give power to the starter solenoid. If the key is off the engine spins without starting (such as when adjusting valve clearance). But with the key on, giving power to the fuel pump, cranking the engine can make it start and run.

If the engine doesn’t crank with the key:
Key on / pins 11-14 wired = if the engine cranks, the key is the problem.
Key on / pins 11-14 wired = if the engine doesn’t crank, the key is not the problem.
Follow up these tests with more cranking on the key to confirm.

As useful as that test is, my problem turned out to be the starter. I had no cranking on the key so I jumped the pins and… no cranking. To be honest, most Internet diagnosis pointed to the starter anyway. But I was hoping for an easier fix since changing a BMW starter can be a big pain. I smacked the starter body with a long extension and a rubber mallet (using care not to touch the terminals). Follow a couple of whacks with a turn of the key. After the 9th or 10th whack the engine fired up.

After all that guess I need a starter. And maybe some better grounds just for good measure.

Update 1: a new Bosch starter did not resolve the no crank issue.

The starter swap went smoothly and took just under an hour. But when I turned the key there was just silence, like before. I jumped pins 11 and 14 again and it cranked. Interesting. I let it crank but it didn’t actually run. After checking connections for ten minutes I was able to get it to run but it was very very rough. I plugged in a Peake scan tool and there were tons of codes – coolant temp sensor, fuel injector #3, air flow meter, etc. I cleared them instead of recording more. When I checked again there was only the coolant temp sensor fault. I checked spark plug wires and the idle control valve and some other connections and started it again. This time it ran smoother but idled low. I know I have idle and throttle position sensor issues. The TPS is not perfectly set and I have tinkered with the idle control screw on the throttle body. Perhaps in my reassembly after the starter swap I knocked something loose? I raised the idle via the screw and that helped. After the engine warmed up a bit the misfire, or whatever it was, cleared up and it sounded as good as before. But the no crank issue continues to be an intermittent and annoying problem.

I’m going to go through the grounds next. It sounds like a good idea even if it doesn’t fully fix my issue.

I will also pull the steering column covers off and inspect the ignition wiring.

Update 2: don’t use FedEx Smart Post for shipping – it takes forever. Even though I’m not in a hurry it’s just annoying knowing I could have had the order in half the time. 

Update 3: the starting problem is getting worse. I have plenty of cranking power but it does not want to catch for the first 30 or so cranks. Then when it does it runs really rough.

The fault code for the coolant temp sensor persists. After reading on the excellent site  www.e30zone.com, the blue coolant temp sensor on the thermostat housing tells the ECU to richen the fuel mixture until the O2 sensor is warm enough to control fuel mapping. It’s a replacement for the cold start fuel injector (the “7th injector”) used on earlier systems. Why am I getting the code?

E30zone recommends a procedure for testing the wiring and sensor using a multimeter. I started with the sensor and it tested fine! That could really only mean one thing: wiring. Ugh. 

Update 4: the C191 connector for the fuel injection harness was full of corrosion. The pins were that special shade of blue that promises to shelve any plans of conducting electricity through them. I replaced the C191 connector with a Deutsch connector. And still the engine cranked but did not start.

Update 5: after confirming the Deutsch connector is passing current I pulled the ECU and checked for corrosion and found none. I then checked the file loaded on the Ostrich chip emulator in case it was corrupt or missing (it passed). So the ECU is probably functioning normally. 

On to fuses and relays. On my Euro 1980 323i there doesn’t appear to be a fuel pump relay. And my relays are arrayed differently than the images for a US 320i online. There is a fuse though so I pulled it out, inspected it, rubbed a little Scotch-Brite on the contacts, and reinstalled it.

There is a series of relays for the E30 M20 – DME, O2 heater, and fuel vapor purge valve. From the notes on the M20 swap wiring I found that the green/violet wire on one of the relays mates to the fuel pump power in the E21 harness. So I jumpered pins 30 and 87 and it fired right up!!! Bad relay? I plugged the relay back in and it still started. Maybe loose or faulty relay operation? It was a new relay when I installed the engine but I will carry a spare anyway.

I let the car warm up and had a functioning temp gauge and the engine revved and sounded fantastic so my C191 fix was a succces. Maybe I’ll get a few more driving days in before winter storage. 

E30 M20 Starter Problems

Hazard Switch Blues

The weakest link in the E21 failed on me tonight. A lot of electrical components run through the hazard switch (it has 15 connections on the back). When the switch fails, it’s a brownout for your E21. Luckily I was carrying a spare.

I also have a short somewhere that pops fuse 17 and I don’t know if the failed hazard switch is related to it.

I went to dinner tonight and left the car in reverse when I parked. When I started the car it cranked longer and when it finally started the hazard lights were flashing. My voltage gauge was flickering between 10-14. Now that I think about it, the door buzzer did was not working when I opened the door (run through fuse 17).

With the hazard switch malfunctioning, and fuse 17 blown, I lost the front parking lights, turn signals, instrument cluster lights, digital clock, door buzzer, and interior lights. The headlights and taillights still worked though so I was able to make it home at dusk.

Luckily after reading the frustrations of other E21 owners I bought a cheap replacement switch to carry as a spare. I popped the new switch in and replaced the fuse and all was good. It’s easy to replace the switch from the top. I put the original switch in as a test and the fuse blew again. Problem solved? Was the switch the source of my fuse 17 issue all along?

Hazard Switch Blues

Reviving A Dead Optima Red Top Battery

I stupidly left the key on in my 323 for over a month. I don’t know how quickly the battery drained but it wasn’t completely done – the trunk light was still dimly lit but nothing else. 

This was a brand-new Optima Red Top and I wasn’t about to spend $150+ on a replacement. Unfortunately, neither of my chargers was having any success. Fortunately, the Optima website is very consumer-friendly and not only did it explain why my chargers didn’t work, it had fantastic instructions for reviving a spent battery.

My off-the-shelf, generic chargers have their own logic that will abandon the charging process if it detects battery voltage to be below a certain threshold. My dead Red Top was down to 1.5v according to my multimeter. The charger will give it a hearty try but call it a lost cause if the voltage can’t be maintained above X.Xv. 

The Optima website gave three options:

  1. buy the correct charger for an AGM battery that will not give up
  2. use the Optima as a slave to a good battery as the master (and keep the master charged)
  3. bring it to a professional shop who will do either 1 or 2

I opted for #2 because I can’t turn down an opportunity to learn a new skill. I bought a set of jumper cables (always good to have those anyway) and connected my Honda battery to the Optima. Right away I had 10.2v at the Optima. 

Then I connected my strongest charger to the Honda battery. I checked voltage every 15 minutes and in under an hour I had 13.4v on the Optima!

I then disconnected the jumper cables and put the trickle charger back on the Red Top and let it do its thing. After two hours it was still going! I had infused enough electrons into the Red Top that the charger’s fuzzy logic accepted. I let the charger work overnight and it continued to put out over 13.5v the next morning. I drove the 323 to work that day with no issues and the voltage gauge reading over 13v the whole time (between 12-14 and closer to 14).

I guess you can say “I’m charged up!”

Reviving A Dead Optima Red Top Battery

E21 Winter 2016 List

List of things to do this Winter:

Finish garage wall! Can’t do much when I have one of the walls under construction. And I need to plan the layout to allow me to work in the Winter. The original M20B23 engine is on an engine stand and more in the way than I expected. COMPLETE!

Complete the wiring for the M20 swap. It’s all there and connected and everything works. I just have to run the sheath over it and plug the metal connectors into the right places on the fuse box plug and C101 plug. I’m only using 7 pins but there are 20+ connections so I have to get it right the first time. I have a few spare connectors but it still makes me nervous. Then I have to mount the C101 connector on the firewall. COMPLETE!

I also need to connect the VDO oil pressure and oil temp sender. Edit: this is not going to be as simple as screwing it on and plugging in some wires. The owner’s original wiring is incomplete. I’ll have to re-do that too, all the way back to the gauges.

Then install the cowl cover and the engine swap should be 99.9% complete. COMPLETE!

I should set the idle speed to a more normal 750-800 RPM. It’s still up over 1,000 to keep it from stalling, but the O2 sensor seemed to take care of it. I might have to wait for warmer weather to do this though.

The temp gauge only gets to 1/4 on the gauge. I’m running the standard E30 80* thermostat and E21 fan. With a cold temp the DME richens the fuel mixture. I can adjust the fuel map but probably better to have the temp in the right place before I start tuning. First I’ll try removing the fan (done.). If that doesn’t work I’ll install a 88* thermostat. 

Other work on the engine should be: check the bottom end and make sure the rod bolts are tight and there are no spun bearings, and check for any leaks. COMPLETE! Bearings look great. A few small leaks from loose bolts and hose clamps. 

While I am around the subframe I need to replace the tie rod boots because they are ripped (COMPLETE! What a job to get the inner tie rod off!). And finish rust-proofing and painting the frame rails.

On the inside, I have a full Euro non-A/C center console to install. That will mean removing the radio (maybe a new one?) and reinstalling it in the normal horizontal position (COMPLETE! Center console is installed and looks great!). I need to fix or replace the radio antenna. I need to fix a few pieces of the center console before installing it. And I don’t have any hardware for it (COMPLETE! Hardware was sourced from Lowe’s and it looks great). At the same time I need to fix the heater controls because the temp and the vent knobs don’t move. I’m hoping I don’t break anything. And I want to check the hazard light switch because they are a known to be problematic (I bought a backup to have).   

how I want my interior to look

I don’t have the ECU mounted. It’s just dangling on the floor (COMPLETE! Mounted to the firewall. The glovebox closes too. Need to tidy up some other interior pieces and I’ll be ready). I want to try the Ostrich emulator so I can make tuning changes on the fly. And I have to recalibrate the wideband O2 sensor in the Spring (COMPLETE).

Lastly, I need to modify my battery hold-down tray so the Optima battery fits in it. It was supposed to fit but Optima must have changed the case and the battery tray manufacturer didn’t come out with a new one. 


I also installed new hood and trunk BMW emblems (roundels) and new wheel emblems.

Wow that seems like a lot! I’ll probably go down this list in order rather than pick and choose. But it all needs to be done before I can really start driving the car in 2016.

E21 Winter 2016 List