1990 316i (M40B16) Issues

[omera60]

Hi All,

I've been lurking around here for some time and decided to join in. My name is Omer and I'm from Istanbul/turkey. I have a 01/1990 316i Saloon Auto Non-CAT 61000km's on the odo. I've been having some issues with it that I need to ask your opinion about. The car runs great in terms of feel when it's hot but when cold starting if I give it gas it hesitates but just briefly after 1-2 minutes it won't do it again. I2ve been all over the place including my very friendly dealer who allowed me to work in their workshop with all their equipment, after some testing and diagnosing I saw that some of the values that BMW provides in their repair manual don't match up with my car, this is what I got so far:

Load Signal tL should be 2ms but I get 1.65-1.85ms
Injection time tl should be between 2-3ms I get 4.35ms
AFM Up/Uv voltage ratio should be between 0.200-0.300V, I get 0.175-0.194V
FPR when checked shows 2.1 ish bar at idle, if I disconnect the vacuum line it rises up to almost 3 bars

When I took these values the engine temperature was 93C, BMW states these values are true for engine temp above 80C.

The rest of the values are spot on (except O2 sensor as it is not present in my car)

The idle is somewhat steady as it idles around 800rpm's, sometimes dips down to 760rpm. The list of things that I changed/done to amend the problem, unless stated otherwise all parts are brand new from BMW, all of them were ordered with chassis so all part number have been checked and are correct:

-New TPS
-New CPS
-New ICV
-New Injectors (Bosch)
-New FPR (Bosch 3bar)
-New vacuum lines
-New fuel pump (Bosch)
-New AFM
-New Exhaust
-New Spark plugs (1k Ohm)
-New Cap
-New Rotor
-New Coil
-New Battery
-New relays for DME and Fuel pump
-New valve seals
-New Air filter
-New fuel filter
-Used known to be good DME
-New Belt and pulleys
-New temp plug (blue plug)

Performed numerous smoke tests without detecting any leaks, the throttle plate adjusted accordingly. Checked for signals from wiring to DME socket, all values are correct and as should be. Did compression test, all cylinders are between 10-11bars. Checked CO, it is in spec according to the repair manual. Fuel delivery from the pump is correct. CPS sits at 0.9mm from the damper.

Some pictures:

BMW Values from the Repair Manual:

IMG_3025.PNG

Fuel Pressure on the rail:

IMG_3341.jpeg

Engine vacuum at idle:

IMG_3093.JPEG

Any ideas on what may cause this? Hope to hear your opinions from you guys...

Best,
Omer

[Brianmoooore]

Have you checked the camshaft timing? This could account for the none too great idle vacuum.
Dowel in flywheel and straight edge on square section of cam. M40 cam pulley isn't dowelled to the camshaft.

Fuel pressure on gauge minus vacuum shown on the other gauge should equal the pressure written on the fuel pressure regulator. I.E. The vacuum in the inlet manifold is equal to the difference between the fuel pressure with the regulator reference pipe connected and disconnected.

[omera60]

Have you checked the camshaft timing? This could account for the none too great idle vacuum.
Dowel in flywheel and straight edge on square section of cam. M40 cam pulley isn't dowelled to the camshaft.

Fuel pressure on gauge minus vacuum shown on the other gauge should equal the pressure written on the fuel pressure regulator. I.E. The vacuum in the inlet manifold is equal to the difference between the fuel pressure with the regulator reference pipe connected and disconnected.

Thank you very much for the prompt reply

This is where I have my doubts, although I have a great mechanic team with me, and the person who changed the belt is an old bmw technician who grew up with these cars I’m not sure if it is done properly. He used the special tool to lock the camshaft and crankshaft in place and then adjusted the belt accordingly but he told me that if he does it the bmw describes it on the repair manual the belt wouldn’t fit over the Cam sprocket. I will double check this with someone else just to be sure but as a side note, the DME shows the timing as 17°

Do you think there is less vacuum on the manifold then there should be and thus this is causing low fuel pressure via the FPR?

[omera60]

Brian,

I will have the timing belt checked as soon as possible but would you have any more suggestions for me regarding the issue? I really appreciate your knowledge and help

[Contours]

I have a similar issue with my 316i which hesitates on taking boot at immediate start up --very much like a vacuum leak. The car also shows a poor vacuum reading at idle. After this initial stumble it will fly for the rest of the day, never cut out and good enough power (for a 316). I think I read somewhere that some engines do not show good vacuum because of their layout so eager to find out also what Brian thinks.

[omera60]

I have a similar issue with my 316i which hesitates on taking boot at immediate start-up --very much like a vacuum leak. The car also shows a poor vacuum reading at idle. After this initial stumble, it will fly for the rest of the day, never cut out, and good enough power (for a 316). I think I read somewhere that some engines do not show a good vacuum because of their layout so eager to find out also what Brian thinks.

Exactly what I am having as a problem if I put aside the numbers etc. The car will run great, will go flying down the road no problem besides the occasional issue of it cutting out while reversing up a hill and I let go of the throttle quickly. From my data gathering, I see that something's upsetting the engine and it's trying to compensate by adjusting the values but not too much that it won't run. The main issue that led me to believe it's a vacuum problem is that the idle vacuum can't even pull the AFM flap to the correct position thus the low variable voltage signal.

Just to confirm I did a smoke test at my dealer with my friends and it seems that there are no leaks. The issue I am currently focusing on is the wrong adjustment of the camshaft sprocket while tightening it thus leading to a somewhat of "wrong" timing. Since the numbers, I am chasing are so close to each other. I am looking for something very tiny

[Contours]

Does feel and behave like a vacuum leak which is compensated for as the engine warms up. It is such a very temporary and minor issue for me that I have not invested much time in solving it. I can see it being a problem if you had to accelerate quickly into traffic in town maybe following a cold start. There is 350k miles on my original engine so bound to be some wear and tear whether that is contributing factor or not. Apart from spraying carb cleaner in the various ports and outlets I haven't found a vacuum leak either. Maybe, there is a leak under the manifold or the throttle position sensor or AFM needs adjustment. As you say it is something minor as the car behaves impeccably after this initial hiccup.

[omera60]

Hi,

So I checked my timing belt and made a small adjustment. I don't feel a major difference but will report back again after a cold start and then check the values again. In the meantime, if you guys have any suggestions I am all ears...

[omera60]

Update; The issue has not been resolved. What do you guys think I should check now?

[Brianmoooore]

What was your CO level at idle? You said it was within spec. but didn't give an actual reading.

[omera60]

What was your CO level at idle? You said it was within spec. but didn't give an actual reading.

Hi Brian,

When I last set it not too long ago it was 0.7% vol. But just to be sure I went to my MOT exhaust test which gets the device calibrated every month by the government, and to my surprise even though no one touched it (CO Potentiometer setting was 2.8V as per BMW repair manual) the test came out as follows;

CO: 0.26% vol
CO2: 16.39% vol
O2: 0.00% vol
HC: 133.00 ppm

So while it was hooked up I made the required adjustment with the AFM screw and the new values are;

CO: 0.74% vol
CO2: 17.17% vol
O2: 0.00% vol
HC: 192.00 ppm

Although I can't test the cold start now the hot idle seems a lot smoother. I went to my BMW Service to hook it up to ISTA to get the latest values off DME and here they are:

IMG_3408.jpg

IMG_3409.jpg

IMG_3410.jpg

As you can see there are some improvements and some step-backs such as the injection timing going down which is good to Up/Uv variable voltage dropping even lower than it was before. The good news is I also crossed checked the vacuum leak theory as the O2 on my exhaust test came 0 which means I don't have any, conclusive with the smoke tests.

[Brianmoooore]

CO: 0.26% vol
CO2: 16.39% vol
O2: 0.00% vol
HC: 133.00 ppm

Not surprised it's idling a bit rough. Those figures are only just shy of what's required to pass a UK emissions test for later cars that are fitted with a cat.
Set the CO a bit above the centre of the range that BMW specifies. Closer to 1% than 0.7%.

[omera60]

CO: 0.26% vol
CO2: 16.39% vol
O2: 0.00% vol
HC: 133.00 ppm

Not surprised it's idling a bit rough. Those figures are only just shy of what's required to pass a UK emissions test for later cars that are fitted with a cat.
Set the CO a bit above the centre of the range that BMW specifies. Closer to 1% than 0.7%.

I did a cold start but the issue is still persistent.

I wanted to ask you about the throttle stop, I believe it has been tampered with before and we corrected it by using the value on the wiki, is this value correct for M40B16 or is there another way of correctly adjusting it?

The surprising thing is that after tampering with it some of the values changed for good some of them worsened. Is it better to run the engine richer than specified? I need to go back to the station to adjust the value again.

[Brianmoooore]

There's no official measurement for the throttle stop. It's set by replacing the ICV with a BMW special tool, consisting of a dummy ICV with a fixed orifice, and then adjusting the throttle stop for a specified RPM.
In the absence of the special tool, I block off the ICV completely, and adjust the stop for a VERY lumpy idle just above the point of stalling the engine.
The engines are specified to run as lean as possible without misfiring at idle to keep emissions down. Sometimes slightly too lean, so upping the CO a bit from the specified level, but still within spec. makes for a smoother idle.

[omera60]

There's no official measurement for the throttle stop. It's set by replacing the ICV with a BMW special tool, consisting of a dummy ICV with a fixed orifice, and then adjusting the throttle stop for a specified RPM.
In the absence of the special tool, I block off the ICV completely, and adjust the stop for a VERY lumpy idle just above the point of stalling the engine.
The engines are specified to run as lean as possible without misfiring at idle to keep emissions down. Sometimes slightly too lean, so upping the CO a bit from the specified level, but still within spec. makes for a smoother idle.

I performed the throttle stop procedure, I had to put some in to keep the engine running otherwise it would stall. I also increased the CO to 1% vol. You were right the idle is incredibly smooth now, I just came back home now I will do a cold start to see on how the main issue is, however after making the adjustment to the throttle screw I noticed that the Up/Uv signal went up to 0.194v.

What else is there to perform/check now?

[omera60]

Well, the issue is not gone but considerably better. The readings are still out of place but there is a general improvement in them. Quick question, what may cause a low manifold vacuum if there are no vacuum leaks and compression on all cylinders is perfect as well as good timing?

[omera60]

Small update;

I got myself a NOS throttle body and replaced it, reset the DME adaptation values by removing negative battery terminal for more than 10 minutes. Bad news is although it was slightly better afterwards the issue is still present. Any ideas on how I should proceed?

[omera60]

After driving around for sometime and it seems to be really good. I hope this is permanent. The manifold vacuum is good now after the throttle. I haven’t hooked it up to ISTA yet nor I didn’t check if there is any change in CO department. I don’t plan on hooking her up to ISTA as she drives ver good now and I don’t want to get upset but I feel like a CO test might be in order to monitor the situations and make sure she isn’t running rich or lean (After this throttle replacement and reset I feel like it is a bit more thirsty then she usually is).