M20b25 Running Rich / Failing MOT emissions test

[JakeusSnakeus]

Hi All,

I thought I'd start a thread about this as I've been struggling to make any major progress so far and any help would be greatly appreciated!

Ok so the car is an 88' 325i and as far as mods go the engine is stock.
Symptoms are bogging and hesitation from idle and at low rpm. Anything after 1000 / 1500 rpm is ok. The car starts, idles, revs and pulls well otherwise. If you blip the throttle at idle rpm's drop.
From cold the engine is much more responsive and appears to get worse as it reaches temp. All 6 plugs are black with soot after running for a short time.

The un-burnt fuel and fumes from the exhaust cause disorientation and temporary blindness lol its really bad, figures from the gas analyser:

----------------ACTUAL------------LIMIT---

CO Fail--------10.14%---------3.50 max

HC Fail--------1258 ppm-------1200 max

Idle Speed: PASS
Smoke Level: PASS
------------------------------------------------
After making adjustments to the mixture screw and re-testing it was not really any different....


Stuff I've replaced so far:

• New Bosch plugs
• New Dizzy + Rotor arm
• New Blue Temp Sensor
• Fuel pressure regulator

Troubleshooting I've done:

• There doesn't appear to be any vacuum leaks, after using a spray bottle and scannerdanners suggested method of looking listening to see if any water gets sucked in i couldn't hear or see anything...
• Measured resistance of the blue temp sensor from the ECU connector, readings look ok.
• The AFM appears smooth and electrical resistance fluctuates as it is moved
• Measured the resistance of the IAT which was 2860 ohms at an ambient temp of 15.5 deg C. I also blew hot air into the air box with a hair dryer to make sure it fluctuated which it did

Things I've noticed:

-A strong smell of petrol from the oil cap

-What is this supposed to connect to? If plugged up rpms drop and idle is lumpy.



-Whats this unused connector for? Something to do with the carbon canister? I didn't find one...



What do i do next????

[kam-325i]

The thing in the red circle should have a bung on the end.
The circled connector looks like the one for the TPS switch under the throttle body, Have you checked the operation of the TPS switch at all ?

[JakeusSnakeus]

Hey Kam,

Not tested the TPS yet I'll post my findings tomorrow evening..

I've also noticed I don't have an o2 sensor in the exhaust. The connector has a what looks like a factory bung in the end

[jimbom30cab]

Yes, your car is too old for an 02 sensor

I would also check under the throttle body. Many M20s have a port under there which would have a rubber bung on. The rubber bungs don't last long as it gets pretty hot under there. Without this bung your vacuum will be pants.

Easy to check the TPS, it should click like a mouse as soon as you pull open the throttle cable.

Whilst the Throttle body is out, check the TPS is not drenched in oil also. Give it a clean with carb cleaner

Let us know how you get on and update the thread.

[Brianmoooore]

What were the actual figures from the blue temp sensor test at the ECU plug, and which pins did you test at?
Your gas test figures indicate a mixture of somewhere around 11:1, which is seriously rich - too far out to be caused by missing rubber bungs and the like (which would actually improve the figures.)
What is the type number of your engine ECU?
Any signs of anyone ever playing with the throttle stop on the throttle body, or the CO adjustment on the air flow meter?
What state is the air filter in?

[HairyScreech]

If those gas measurements were done at idle then it can be a false rich.

Air leaks (unmetered air not from the AFM) on these things seems to cause an idle misfire, that actually tests as rich despite the reason for the misfire being a lean condition.

Is it rough at idle?

You need to get that hole plugged then pop the battery off, let the ecu discharge and then let it relearn the idle without that big leak.

If that does not cure it then the next places I would be looking is the gaskets from the inlet manifold to the head, these go hard and crack, leaking air like a sieve.

I have been through this one myself.
A big enough air leak will give a roving misfire that dumps fuel into the exhaust and tests rich.

[Brianmoooore]

If those gas measurements were done at idle then it can be a false rich.

Air leaks (unmetered air not from the AFM) on these things seems to cause an idle misfire, that actually tests as rich despite the reason for the misfire being a lean condition.

Is it rough at idle?

You need to get that hole plugged then pop the battery off, let the ecu discharge and then let it relearn the idle without that big leak.

If that does not cure it then the next places I would be looking is the gaskets from the inlet manifold to the head, these go hard and crack, leaking air like a sieve.

I have been through this one myself.
A big enough air leak will give a roving misfire that dumps fuel into the exhaust and tests rich.

I'd agree with the above if it wasn't for this: " All 6 plugs are black with soot after running for a short time."
Fully agree that a mixture that is too weak to ignite will, of course, pass straight through and raise the HC sky high, but not the CO so much, or give black plugs.
Also I'm not over looking the possibility that this car has had a problem in the past that led to lean running, for which a bodged 'cure' has been made in the past by increasing fuelling, and that the original fault has now been cured by the OP's present work, which has now left the over fuelling.

[HairyScreech]

This is true, my plugs were not too bad when I was suffering from air leaks.
The CO I honestly cannot remember.

I think it is likely that there has been some cover up work in the past.

OP - Was the screw for the mixture adjustment already exposed or was there sealant over it?

[JakeusSnakeus]

Hi Guys,

Thanks for all the posts.. some answers for you:

-TPS
I can hear it clicking although I've not had the throttle body off yet to check what state its in at the moment but i did blast it out with some carb cleaner a few weeks back

-Blue plug figures:
Grounded on pin 24 and positive on pin 45

Cold: 3280 ohms
Warm: 352 ohms

-ECU
Here


-

Any signs of anyone ever playing with the throttle stop on the throttle body, or the CO adjustment on the air flow meter?

Probably yes i cant say for sure. The screw on the AFM was quite high up originally but it was screwed down at the MOT station in an attempt to reduce the readings

-Air filter
Its quite clean and looks ok

-Idle
Idle is good tbh there is a very slight miss every so often that you cant really hear but if you put your hand on the rocker cover and feel for vibrations you get a slight random shake every now and again. This could well be the plugs though as they keep getting caked.

Was the screw for the mixture adjustment already exposed or was there sealant over it?

I'm sure it was already exposed

I don't doubt the possibility of a bodge job in the past the previous owner was far from an honest man, put it that way.

I've also recorded some video's of tick over and throttle response from cold and again from hot if you think it might be any use? Let me know I'll upload them.

[JakeusSnakeus]

Also what pins do you probe to test the IAT from the ECU connector?

[Brianmoooore]

IAT sensor is pins 1 and 4 at the AFM, and pins 44 and 26 at the ECU.
Your blue temp. sensor results look spot on, and testing at the pins you did includes the plug and socket under the inlet manifold and the earth wiring all the way to the battery terminal and back again.
Time to start checking the fuel pressure, I think. Double check that your new FPR is the correct pressure rating (marked on it), then either tee a pressure gauge into the supply pipe, or disconnect the return hose from the FPR and connect a piece of hose from it into a can, in case there is a blockage in the return pipe.
What colour are the plastic parts of your injectors?

[JakeusSnakeus]

Injectors are light grey. The regulator is a 3.5 bar. I've got two spare, a 2 bar and the original 3.5 i took off.

Do you know what sort of readings to expect from the IAT?

I'll do some testing on the fuel pressure and post an update.

[Brianmoooore]

164 ECU is correct (87-88 M1.3 2.5 litre). Any signs of it having been opened up?

My notes say IAT = 3000 ohms at 10 degrees, decreasing with increasing temp., so your figure sounds about right.

Injectors light grey or light blue? M20B25 should be light blue.

[JakeusSnakeus]

I'll open up the ECU and have a look, could have been messed with you never know..

IAT sounds good then, ill re-test at the ECU plug just to make sure.

The injectors definitely look grey...

[Brianmoooore]

See if you can read the Bosch part# of off the injectors. Your best chance is on the coloured bit of #1 injector, looking at it sideways, under the fuel pressure reg.
Number should be 1280 150 xxx.

[HairyScreech]

I have a set of 2.5 injectors here that look grey, almost like the blue has faded to a really light blue/grey.

Pn will show which they are for sure.

What plugs have you got in it?

[JakeusSnakeus]

Plugs are Bosch Super Plus

Injectors are a light blue i was looking at the connectors.. ha must of been tired. Numbers i could see where

752
280150715

either tee a pressure gauge into the supply pipe, or disconnect the return hose from the FPR and connect a piece of hose from it into a can, in case there is a blockage in the return pipe.

I've been avoiding buying a pressure tester. Having the return feeding into a petrol can isn't really viable it fills up in about a minute and a half... ill see if i can borrow a tester from someone.


Also I've opened up the ECU but haven't had time to check the eprom chip. Any idea's on what i should be looking for? does the standard chip have any markings?

[Brianmoooore]

Injector # is correct for your car, so over sized injectors isn't the problem.
Lose the Super 4s. M20s don't run well on four electrode plugs.
You can buy a fuel pressure tester that's good enough for your purposes for about £10 off of ebay.
Standard 'chip' has markings; modified 'chip' usually has less 'professional' markings.

[HairyScreech]

As above, ditch the plugs for some NGK BPR6ES plugs.

[JakeusSnakeus]

ok cool i've ordered some NGK's

I've got a vacuum pressure gauge but its not designed for liquid what did you find on ebay for £10??

[brian_s]

Watching with interest as I'm in the same situation! Hope you get to the bottom of it!

[JakeusSnakeus]

yea me too i just want to go sideways again!

Can you take the top board out of the ecu to get to the one below with the eprom on it? The top board looks like its soldered to the connector directly.

[JakeusSnakeus]

Hello.. Sorry for the delay...

Changed the plugs to NGK BPR6ES as recommended.

I've fitted a pressure gauge to the car on the incoming side of the fuel rail, pressure is quite consistent around 2.5 bar at tick over and when revving the engine it only fluctuates slightly.


Still no improvement.

[brian_s]

Damn I was hoping you had got to the bottom of it so I could copy

[HairyScreech]

What ECU number have you got in there?

BMW part number is on there somewhere. Will be either 11 or 7 digits.

[Speedtouch]

yea me too i just want to go sideways again!

Can you take the top board out of the ecu to get to the one below with the eprom on it? The top board looks like its soldered to the connector directly.

You can unclip them at one end and prize them apart as far as the ribbon cable will allow - usually about an inch or so. To remove the top board would entail desoldering the ribbon cable.

[Brianmoooore]

Has this car ever passed an MOT emissions test while in your ownership?

[JakeusSnakeus]

Numbers i can see on the ECU are

Red Bosch label
0 261 200 164

other label?
1722190 001

Picture of ECU

I also checked the valve clearances which where all within reasonable limits. I gave the rocker cover a lick of paint too.

[JakeusSnakeus]

Yes it has passed an MOT before i don't have the previous readings from the previous mot tho..

[minesapint]

Can you take the top board out of the ecu to get to the one below with the eprom on it? The top board looks like its soldered to the connector directly.

This is an ECU 073, out of 86 325i Cab, but I think the idea is the same.



This is an easy step provided you take care.
The eprom base is bottom left on the PCB, & my original chip is bottom left. Note it is 24pin & the new chip I bought from a zoner on here was 28pin, (chip on right) 28 doesn't go into 24. Beware.

Cheers

[JakeusSnakeus]

Hey man thanks for the post but i don't think my ecu is the same as that.

On mine the top board is soldered to the 55pin connector

[minesapint]

Also I've opened up the ECU but haven't had time to check the eprom chip. Any idea's on what i should be looking for? does the standard chip have any markings?

Sorry I missed showing the markings on a standard chip



Here at the bottom

Cheers

[HairyScreech]

Ok, the ecu is correct,

325i 2.5 litre (6 cyl)
87-88
Bosch Motronic 1.3

0 261 200 164

12 14 1 722 190
12 14 1 722 430

XEBM0164

[JakeusSnakeus]

Sorry I missed showing the markings on a standard chip

I found this video (although its not the same ecu) that suggests you can push the top row of pins back in to release the top board

[youtube][/youtube]

I'll have another look tomorrow to see if i can get it to come apart so i can see the markings on the chip...

If it ain't this i guess i got to pull the injectors

[JakeusSnakeus]

Ok, the ecu is correct,

325i 2.5 litre (6 cyl)
87-88
Bosch Motronic 1.3

0 261 200 164

12 14 1 722 190
12 14 1 722 430

XEBM0164

Good to know, thanks.