1979 Other BMW Models BMW 633csi Cold Running Issue

Try replacing the coolant temperature sender.

[quote:f72f8dfe79="Dr. Hagerty"]Try replacing the coolant temperature sender.[/quote:f72f8dfe79]

Thanks for the quick reply!
Isn't there a way to test the coolant temperature sender by looking at resistance?

It is a negative coefficient type sensor and I dont know the parameters. It will also need to be accurate at the "brain" not just the correct resistance at the sensor, inspect the wiring and the connectors.

[quote:0012320ccd="Dr. Hagerty"]It is a negative coefficient type sensor and I dont know the parameters. It will also need to be accurate at the "brain" not just the correct resistance at the sensor, inspect the wiring and the connectors.[/quote:0012320ccd]
Ok, thanks!

I think a "hot" resistance of about 80 ohms was normal for that sensor, try substituting a carbon film resistor in its place.

[quote:f67ef95ce1="Dr. Hagerty"]I think a "hot" resistance of about 80 ohms was normal for that sensor, try substituting a carbon film resistor in its place.[/quote:f67ef95ce1]

I was actually looking at this sensor earlier today, and it seems like if I was looking at the right one, there was only one electrical connection on it. Is that right? I'm looking at a sensor going into the coolant housing/passage at the front of the engine, close to the radiator. There was a second wire very close by, but nothing to connect it to.

It will be a sender with a single lead that goes to the L-Jetronic brain. I will call my sources in San Diego today to see if I can get more info to you.

[quote:c4a2d7ea28="Dr. Hagerty"]It will be a sender with a single lead that goes to the L-Jetronic brain. I will call my sources in San Diego today to see if I can get more info to you.[/quote:c4a2d7ea28]

ok, that would be great!

Sorry I haven't got back sooner. My source was not available and I will try again tomorrow, stay tuned.

[quote:bf7e9fdb46="Dr. Hagerty"]Sorry I haven't got back sooner. My source was not available and I will try again tomorrow, stay tuned.[/quote:bf7e9fdb46]

Ok, I replaced the coolant temp. sender, and there doesn't seem to be a difference.
What should I go after next?
Also, the "reactor" and "egr" test panel lights are on... could either of these cause the cold running issue?

The reactor and EGR lights can be reset from under the car. Follow the speedo cable to the box with two "buttons" on it. Push to reset. The cold start issue could also be the cold start system is inop, does the Thermal time switch have power to it? Has the cold start valve been tested?

[quote:f19ab29602="Dr. Hagerty"]The reactor and EGR lights can be reset from under the car. Follow the speedo cable to the box with two "buttons" on it. Push to reset. The cold start issue could also be the cold start system is inop, does the Thermal time switch have power to it? Has the cold start valve been tested?[/quote:f19ab29602]

Ok, I'll reset the lights, but could the EGR system have an effect on the cold running problem?... I've heard EGR valves aren't supposed to open when cold.
I haven't tested the voltage on the Thermal time switch or the cold start injector itself. However, I disconnected the fuel line to the cold start injector when I turned the car off one day and the cold running issue remained next time I started it up (fuel line still disconnected from cold start valve).

EGR does not usually show up as a cold start issue. Cold start requires the cold start valve has fuel pressure and a signal to work correctly.

[quote:c8b6f095da="Dr. Hagerty"]EGR does not usually show up as a cold start issue. Cold start requires the cold start valve has fuel pressure and a signal to work correctly.[/quote:c8b6f095da]

I know that it has fuel pressure, but I don't know for a fact that it has a signal. However, the car has no problem starting up when cold, it just runs very rich when it does (seems like lack of cold start signal would cause it to run too lean at first). Plus it runs poorly for much longer than the maximum 30 seconds or so that the cold start injector would be doing a job.
Seems unlikely to me that it's the cold start injector, I'm just not sure what it could be.

Well you have a 30 year old car with worn parts and a cold running issue, short of replacement of all the possible components including harnesses, there is one thing to keep in mind, how much is this car worth to me? I am not advocating crushing the car, but if there is an emotional attachment here, you may need to do some soul searching. I have worked on older BMW cars and the first thing I tell the people is that this can become very expensive very quickly. If the air flow meter is bad, if the harness has an internal issue, if they have to spend several dollars more than the street value of the car, then they need to know that so that an informed decision can be made and once that decision is made, then a plan can be formed, do we have a plan? Is it complete with every contingency thought out? If not then I can try and help you find one. Lets start with the basics like a baseline of the condition of the power train and engine management systems.

[quote:2ad7d988d8="Dr. Hagerty"]Well you have a 30 year old car with worn parts and a cold running issue, short of replacement of all the possible components including harnesses, there is one thing to keep in mind, how much is this car worth to me? I am not advocating crushing the car, but if there is an emotional attachment here, you may need to do some soul searching. I have worked on older BMW cars and the first thing I tell the people is that this can become very expensive very quickly. If the air flow meter is bad, if the harness has an internal issue, if they have to spend several dollars more than the street value of the car, then they need to know that so that an informed decision can be made and once that decision is made, then a plan can be formed, do we have a plan? Is it complete with every contingency thought out? If not then I can try and help you find one. Lets start with the basics like a baseline of the condition of the power train and engine management systems.[/quote:2ad7d988d8]
That makes sense, the car isn't worth particularly much and I don't want to just sink money into it. I plan to sell it at the end of this summer. I bought it as a project for $400 (without an interior) and I've been transferring the interior from a parts car into it. Naturally, nothing on these cars are in perfect shape, so it's no gem. The car drives and shifts well, but it has a slight steering pull, the cold running issue, and some little things that need attention - tires, oxidized paint on the hood, etc.
However, it's a good looking car with a lot of replaced parts, including tuned suspension, cold air intake, strut brace, and so on.
Basically, I'm reluctant to spend a bunch of money to replace all the worn parts, I'm just looking for an basic idea of what I should be checking into next on this problem... I'm generally more willing to spend time on it than money. I appreciate all your help.

Thank you for sticking with this project. Lets see if we can do some good. Valve adjustment, spark plug gap, cap and rotor, wires, can all be contributing factors, as can throttle plate adjustment and warm up regulator, plus all the plumbing, how does this stuff appear?

[quote:f0d5af4269="Dr. Hagerty"]Thank you for sticking with this project. Lets see if we can do some good. Valve adjustment, spark plug gap, cap and rotor, wires, can all be contributing factors, as can throttle plate adjustment and warm up regulator, plus all the plumbing, how does this stuff appear?[/quote:f0d5af4269]

I just adjusted the valves a couple days ago, including tightening a loose (but still connected) banjo bolt.The valves made it run a little smoother, but the cold running problem persisted. I also replaced the spark plugs, cap, and rotor. I haven't replaced the wires, but they look like they've been replaced relatively recently. It seems that the warm up regulator is probably fine... it gradually brings the idle down to 950 rpm when warm (I adjusted the idle control screw since I originally posted this query). I've looked at the throttle plate and it seems to close completely. In addition, I set the timing a few days ago.
As for plumbing, there were a few problem areas that I've worked on, including a disconnected vacuum line going to the fuel pressure regulator (fixed now), and the leads to the electric valve control on the vacuum advance are broken off (I'll replace this soon from my parts car). I've experimented bypassing this valve and I couldn't notice any difference. Otherwise, I've taken a look and I can't find any gaping issues with the plumbing... vacuum lines seem relatively new and crack free.
As a side project, I'm working on removing the exhaust reactor and replacing it with a non-reactor manifold from a 630csi.

Those thermal reactors are trouble, save them for the future. The spray pattern from the injectors can be an issue or just the fact that it is a 30 year old car with antiquated injection can be an issue.

[quote:048e30145a="Dr. Hagerty"]Those thermal reactors are trouble, save them for the future. The spray pattern from the injectors can be an issue or just the fact that it is a 30 year old car with antiquated injection can be an issue.[/quote:048e30145a]

Well, I've sent through 2 doses of techron injector cleaner in hopes of improving the spray pattern or unclogging injectors, but it didn't seem to make much of a difference. I could take each injector out and look at the spray pattern, but that would be many hours of work because they are so inaccessible, and it seems unlikely that they are bad considering the cleaner didn't make a difference. What do you think?
I have done a fuel pressure leak down test and determined that the injectors are not leaking.

The air flow meter can be a source of this issue, is the AFM original to the car?

[quote:1a24e0b706="Dr. Hagerty"]The air flow meter can be a source of this issue, is the AFM original to the car?[/quote:1a24e0b706]
Sorry for the delayed response.

Well, I installed an air flow meter from my 630csi parts car, and I believe it didn't change this issue (but I changed it in at the end of summerl, so as you can imagine I didn't have much of a cold running issue at the time)
I might try switching to the old one again to make sure switching them didn't CAUSE the issue.

Another thing I haven't mentioned is that the oil level rises the more I drive it and seems to smell like gas. I figure this is just because gas leaks by when it runs insanely rich at cold startup. I think the rings aren't too bad because the compression was high (120 psi or so when specs say around 114).

I'll let you know if the AFM changes anything.

I had what sounds like a similar problem in my 6... It turned out to be a cracked hose from the air box to the AFM... it was on the bottom and we couldn't find it... It rotted from age I guess.
I am fairly certain that was the problem. The only other prob. I had was with my Cat..... knock on wood.

My car has a cold air intake installed... but I seem to remember there is a slight crack where it connects to the air flow meter. Wouldn't this only mean that a slight bit of unfiltered air could get in the engine, but it wouldn't affect driveability? are you sure that's what was wrong with yours?

By now, I've finished the EGR/Reactor removal and I've tried both of my AFMs in the car, but it still has this cold running issue.

You know the early L-Jetronic was so archaic by today's standards that we sometimes forget to check the basics. I cant say I remember the cold start set up procedure but if I had to do a little digging it probably wouldn't kill me, how shall we proceed Captain?

onward march!
I appreciate all the help I can get

also, I read this on the internet...

"Initial Driveability
Model:
1982 633CSi/733I, 1983 533i/633CSi/733i, 1984 533i/633CSi/733i
Complaint:
If the engine is cold or warm, the vehicle will emit a hesitation or have poor throttle response during the first few minutes of starting. This is due to the internal re-programming of the Motronic Control Unit was not able to compensate for the elimination of the external 560 OHM resistor.
Remedy:
Install an external resistor in the NTC line."

I'm not sure which resistor they're talking about, but it sounds like a similar issue on a similar car.

This is a reference to the coolant temp sensor that tells the "brain" the engine temperature. The early M-30 motors are L-jetronic not motronic.

ok, well scratch that.
what should I do as a next step?

Also, is there a way that I can test for sure whether my AFM is working right, especially with regards to it's temperature sensor?

hey... still haven't figured this out.
any ideas?

their are other repairs that can be checked and eliminated in your quest to making this vehicle run efficiantly, In 1986 bmw came out with a campaibn to correct this problem and there were many repairs on this correction list ntc sensor resistor install , carbon blast on intake valves , vacuum pod in air box , carbon canister update and a few more , I made a lot of money that year because of this fix and it spands out to several bmw"s 318,733 so consult in your nearist bmw dealer because this info is free for piece of mind!

I ended up finding the problem with my car... Some water had leaked into the ecu and caused damage. I replaced it and it ran great after that.