New-to-me 1992 735iL – the fun begins!

[E32FAN]

Tried to check the voltage coming from the O2 sensor but could not complete the test, I was getting 20v+ and -10v at two different pin positions. The Bentley isn't clear about the pin assignment .

B203 Oxygen Sensor is shown on Page 1360-05. Connector X6200 pinout is on Page 8500-16.

[Cactuar]

Doh, I was trying to back probe into the actual connector of the O2 sensor. No wonder I couldn't identify the pins.
I'll try again on the onboard connector (female end).

[Cactuar]

Thanks E32FAN, tonight I could see the values correctly using the yellow and black wires.
The voltage fluctuates between 0.2 and 0.8 as outlined in the Bentley manual, so all is well.

The crankshaft position sensor also tested fine at 560 ohms.
The NGK spark plugs are new and gapped correctly.
The coil primary and secondary tested ok.
The spark plug wires tested ok, a bit of deviation from spec but they are within the +/- range.
When removing the oil cap the engine wants to die, the dipstick also has an effect.
No white mayo on the oil cap and the exhaust smoke is clean. It does smell rich/funny though.
The cheap fuel pressure gauge I bought isn't working right so I need to get a quality gauge, then I'll check the fuel pressure.
New fuel filter
New fuel hoses
New fuel pump
New fuel pressure regulator
New distributor cap and rotor
New coil
New voltage regulator
New fusible links
New coolant temperature sensor (blue connector)
Tested a known-good idle air control valve, no change
Tested a known-good air flow meter, no change
Valves adjusted to spec
Changed engine oil, new oil filter
Changed transmission oil, new filter and pan gasket
New air filter
New belts
New blower motor
New vacuum hoses
New throttle body gasket
New injector o rings
New O2 sensor
New fan clutch
New water pump, new coolant
New thermostat
All quality parts
Sprayed brake cleaner all over the upper part of the engine (including the brake booster) and no change in engine speed.

Today I noticed that the hunting is more pronounced when the engine is cold. It's smoother when hot but still there.
It sounds like something is straining the engine at idle, it doesn't sound relaxed, for lack of a better word.
Other than the AC (which is always off on my car, I didn't install a belt for it yet) what else can cause a load on the engine at idle?

Here's what it sounded like tonight.
Btw I might appear obsessed with this issue, but I really want to get this engine perfect. I have a very low tolerance for NVH and this issue is really getting on my nerves!! Thanks to all of you for your help you are a patient bunch!

[a777fan]

This video sounds a lit better (from an idle surging perspective) than previous ones you have posted. Am I perceiving that correctly?

You’ve gone through and changed a lot. As I read through your list, I’m wondering if you have gone through and checked the spin resistance of all the accessories cold, and then done the same again when its hot and the surging is less pronounced. This might turn up something given the behavior changes with temp?

Apologies if someone has linked this for you before, but i found it and it seems to be a very thorough and methodical. Should be good for any motronic bmw 6 with a distributor!


https://www.hpsimotorsports.com/motronic-

[Cactuar]

Yes the idle does sound better when warm, most of the time.

When you mention the resistance of the accessories, do you mean for example that the power steering pump could load the engine?

I did find this guide before yes and tested a few things, but I did not follow it rigorously. Thanks for linking it again, I'll bookmark it and follow it.

[Cactuar]

I have a theory. Could the intake manifold gaskets expand when hot and seal a leak if there is one? Then when cold they would contract and let more air through, resulting in a worse idle when cold.

[a777fan]

Yes the idle does sound better when warm, most of the time.

When you mention the resistance of the accessories, do you mean for example that the power steering pump could load the engine?

I did find this guide before yes and tested a few things, but I did not follow it rigorously. Thanks for linking it again, I'll bookmark it and follow it.

Even without a load. If one of the bearings is going for example.

Something that may be simpler. Take the accessory belts off and start the engine. See if the surging is gone. You wont be able to run it for any true length of time of course, but hopefully long enough to determine if one of them is oddly loading up the engine sporadically.

[Cactuar]

Ok so I took off the belts and started the car... nothing. It just cranked and didn't start.
Checked everything (or so I thought), went to buy fuel because the refill light was on, jumpered the fuel pump...

Then I realized I forgot to plug back the CPS Amateur hour!

Obviously the car started right away, and even without the belts I could clearly hear the hunting of the engine.
So that rules out the water pump, alternator and power steering pump.

[theBMWbeast]

Could be your theory of gaskets expanding with the heat. Might be the next order of business, will also allow you to check the vacuum lines under there when you pull the intake. Good to hear that the dipstick/oil cap test yields positive results. That means it’s not a massive vacuum leak (although it could still have a small one).

Throttle body adjusted/ checked when you did that gasket? Interested to see fuel pressures as well. I know you did the injector orings, have you ever had the injectors themselves serviced? We’re running out of options here, which is good!

[Cactuar]

Thanks for the encouragement!
Correct I took out the injectors and replaced the o rings and did a leak test over 24h but I did not service them. It's mostly a cost issue, like the ignition wires. Both are 200+ CAD each so I'm trying cheaper options first!

The throttle body was thoroughly cleaned and adjusted to 0.002" (meaning it does not close fully) per advice on mye28.com. That adjustment made no difference.

Other than the brake booster hose all the vacuum hoses attached to the intake manifold are new. The brakes work great so I don't suspect the booster hose.
The hose going to the charcoal canister is also original but I inspected it and it's fine.

Edit: just ordered a set of Elring intake manifold gaskets.

[theBMWbeast]

https://www.ebay.com/i/401851488594?...CABEgKMTvD_BwE

I run these injectors in my car, no complaints. I understand some people want to remain stock, however $50 for all 6 brand new injectors is probably cheaper than the rebuilding of original injectors.

Yeah not too many vacuum lines on these luckily.
What specs did you adjust your valves to? Cam side or at the eccentric?

If you have a dremel and some time, you can gasket match the intake manifold when you take it out, smoother airflow and all that jazz. The discrepancy is quite high on the intake ports/ vs the ports on the head.

[a777fan]

No worries on not finding the issue with the belts disconnected, just one more possibility crossed off!

Have you disconnected the ICV while idling to see if that may be causing the surge? I believe when disconnected it stays in the last commanded position, but that may only be the later valves on the M50 and M60.

[Cactuar]

Yes I disconnected the ICV with the engine running and after the idle stabilizes the hunting continues.

I'm not a fan of no-brand eBay parts personally. I'd stick to Bosch if I need to replace the injectors.

Speaking of which, I started the disassembly to replace the intake manifold gaskets.
It's going pretty well, I just need to get some tools to get the lower nuts off as access is quite restricted.

While I have the injectors out, how can I check if the spray pattern is OK, and if the volume of fuel delivered is correct?
Would starting the car without the coil connected activate the injectors? Is there any danger to damage the starter?

[CroughtonE32]

I'm just like you. If I can get OEM, I do. When I changed my six injectors about 5 years ago, I had found that Bosch replaced the factory injector with another. I could have gone with the new ones, but I didn't like the look so I returned them to BavAuto. Then I went on a hunt looking for parts stores that might have had old stock so I could get the exact injectors we were taking out. Took a while but I found a place that had eight of them. Cost me plenty. Almost 90 dollars each. I know that's a lot and rebuilt would have been fine, and maybe even a different spray pattern for a change. But like you I wanted what I wanted so I bought them. I was very happy in the end. I just went on a search for you. Took me all of six minutes and found a shop in Miami that has more than 10 of them in stock. And for half of what I paid for them five years ago. Here's link if you're interested. https://www.ebay.com/itm/Fits-BMW-E2...SBtw#vi-ilComp

[Cactuar]

Don't tempt me Jeff I can't splurge on new injectors yet, maybe at a later time.

[CroughtonE32]

Just thought I'd show you there are still around if you looking for exactly what came in your Car from the factory. Always to good to know.

[theBMWbeast]

Nice detective work Croughton. Bosch is for sure the way to go, the ones in my car are Bosch branded, the newer style like the link I sent. Was around the same price. Those may have been knockoffs, didn’t look too hard. Same part # listed there though. Can’t help you on the injector test.

Hoping these gaskets are going to help or fix the issue, been waiting for an update

[Cactuar]

I could only take off two of the lower intake nuts tonight! I cracked one more but could not take it off fully.
BMW must have felt contempt for their techs by hiding the lower intake nuts behind a coolant hose on the M30!! What a pain.

Really need to get stubby wrenches and crowfoot adapters.

[CroughtonE32]

I could only take off two of the lower intake nuts tonight! I cracked one more but could not take it off fully.
BMW must have felt contempt for their techs by hiding the lower intake nuts behind a coolant hose on the M30!! What a pain.

Really need to get stubby wrenches and crowfoot adapters.

I believe if you lift the cooling hose there might be enough slack for it to come off the hook it rests on held on by the center lower intake manifold bolt. Might be easier to get to the bolt with the hose out of the way. That was the perfect time for me to change that cooling hose. That thing goes in all crazy directions. If you do, stay away from URO with these. Only OEM. I've heard other people have had troubles with URO hoses. Again, one of the things I returned to BavAuto and paid them more for the OEM hose. Only after posting here about what we were about to do and everyone jumped in and said send it back. I listened.

[theBMWbeast]

You should not buy URO anything. Rein works fine in this application

[a777fan]

Hmm. Now that you’ve ruled out the ICV, i think you’re on the right track with some sort of intake leak.

If you had an injector problem, I don’t think it would result in a surging idle issue like you are experiencing. You’d be rich or lean, or some variation on that theme but I don’t think you’d get the engine speed to surge. For example, what is the primary engine speed controller?

Your throttle plate! This controls the amount of air the engine can ingest. More/less air through the system, the faster or slower the engine spins. Fuel is obviously adjusted in kind, but only to maintain the proper air fuel ratio for the best power/combustion efficiency. There is obviously a limit to that analogy, as without fuel the engine would not maintain motion, but I believe its influence on this issue would be secondary, not primary.

But even this secondary influence should be unlikely: Fuel delivery volume is a function of two things 1) pressure at the fuel rail, and 2) injector open duration. That is pretty much it. If you have already confirmed that your fuel pressure is at spec and not oscillatory, there isn’t much else the injectors could be doing to contribute to an idle oscillation. Additionally, in order to do so, all 6 of your injectors would need to be malfunctioning in the exact same way to get this repetitive oscillatory behavior. Pretty unlikely IMHO.

Another thought which you might try if its easy... Unplug and remove the ICV from the system completely. I am not sure how its configured on an M30, but removing it completely and idling the engine will ensure that there isn’t something mechanically odd going on inside the valve causing the metering valve to oscillate even when unplugged.

[Cactuar]

I won't be changing the coolant hose for now, and yes I am staying away from anything URO on my car! I had good luck with Rein though.

Thanks a777fan I'll try eliminating the ICV from the system as a test, after I'm done changing the intake gaskets.

Btw does anyone have a tip on removing the lower 12mm nut on the second intake runner?

intake_nut2.jpg

It's the only nut remaining. I managed to crack it loose but just barely, there is about 3-4 degrees of rotation possible with a regular length 12mm wrench. A socket won't fit because of the coolant hose bracket in the way.
I can't reposition the box end of the wrench so I can get another go at rotating the nut, because of said bracket.
Even a ratcheting box end wouldn't work because of the thicker outer ring.

Any tips would be appreciated thanks!

[theBMWbeast]

That sucks if the gap isn’t big enough to get a socket on it. My recommendation was impact driver and a flexible extension. My car didn’t have that hook when I did my intake.

An offset boxed wrench might work here to clear that hose.
Is there a reason you can’t unclip the hose from the bracket, and give yourself more roof to work with? Or maybe a socket can be forced on if the plastic will give a little; I see an air gap top and bottom. That would be my approach, but obviously pictures are much different than being there. Maybe the offset wrench will do the trick, if you have one.

[E32FAN]

We have been very supportive of Cactuar's sleuthing of his surging cold-engine idle RPM troubles.

Now, let us do a quick Reality Check - how does your M30 cold-engine idle sound?

Me, I'm starting to thinking that (Jay Leno's phrase), "They ALL do that". My car's RPM is a bit erratic until I give it a bit of accelerator juice, and then it smooths out, just like Cactuar's car does.

So, I am wondering, is this M30 rough idle complaint really a thing?

Possibly it is just the way the Bosch DME software works, as normal.

I think we all ride with Cactuar in seeking E32 perfection. So if we are finding a few minor warts, that is fine.

Let's share our observations in this.

[Cactuar]

Thanks Mr Beast. The plastic bracket appears to be molded onto the bent metal tab, I tried to pull on it and it wouldn't move.
Pics of 11531718959 from ECS:
hose_bracket.jpg

Your idea of an offset wrench is a good one.
SK make a short offset wrench with 11mm and 12mm.
I'll shop a bit more but this might be one I order.

87761.png