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eddie
what are your thoughts about the exhaust e21 6 cylinder system or a custom made system perhaps?

Just posted a thread asking exactly that question!

http://www.bmwe21.net/forum/viewtopic.php?f=3&t=22361

It's been too long since an update, been very busy with the car and a new job.

It's a bit of a mixed bag at the moment. The engine runs very smoothly, no lumpiness or misfiring any more, but unfortunately it's revving very high, and I'm not talking a little bit high, it sounds like it's 3k+ and slowly climbing.

This high idle could be cause by the lack of back pressure, as there is not a complete exhaust at the moment, something I'm in the process of sorting. After a chat with Jord, we think it might be injector related, as I had the injectors doing this after the engine stalled:



So I did some reading and it turns out that there were some very early, high impedance injectors, mainly Jetronic. The later cars all had low impedance injectors. The readings for the two types of injectors are as follows:

HI: 14.5 Ohms - 17.5 Ohms
LI: 2.5 Ohms - 3.0 Ohms

I tested the resistance of mine tonight, circa 16.0 Ohms. So it might well be that mine are somehow the wrong ones. The part numbers do vary it would seem, so I'm going to try a set of later ones, and see if the resistance is different, and if so, swap them, if not, back to the drawing board.

I have a very helpful breaker from E30Zone who is helping me no end with spare parts, and trying to find the issue.

ICV might well be at fault, but I'm not convinced it could cause such a high idle. The important thing to remember is the idle is smooth, not lumpy at all, suggesting it's not an air leak, as I believe a massive air leak would cause crappy running.

We tried blocking various things up to see what does what, and the only way to bring the idle down was the block the ICV, and open the hole in the rubber boot between the AFM and the TB that the ICV was in. When we did that, the engine idle dropped, ran rough, then died.

Had a look at the AFM tonight, and it seems spanking new inside, all clean and looked fine. Same story with the Throttle Position Sensor, which was perfect inside, no gunk or crap which is commonly found in there.

Next step is sort the exhaust so I have adequate back pressure. Then go from there.

AFM and TPS measured correctly? Temp senders for intake air and coolant also?

Still need to run a multimeter over them both.

Same goes for coolant temp sensor, but I didn't know anything about an air intake temp sensor?

Intake air sensor is integrated in the AFM's housing. Hard to diagnose from a distance, but either one of these components could cause this. Best place to check would be at the Motronic's connector so you can also exclude any issues in the wiring loom. Still, the fuel injectors are worth a check as well, knew there were versions with different capacities, but I never heard about differences in impedance. Always something to be learned!

So, the high idle is sorted!

It was the simplest, and most obvious thing it could have possibly been! I actually felt pretty stupid once I noticed it!

Anyway, I'll explain myself:

So I looked at the realOEM drawings for the brake booster vacuum hoses and followed them. Anyway the rubber boot I bought from BMW had an outlet on the right, which matched the drawings, so I hooked it up as per the drawing.

I've illustrated it below:

14168432057_35605a7a70_o by Eddie the Kid, on Flickr

Blue line is air passing up the boot to the throttle body.
Purple is throttle body.
Red is air passing up the boot and through the ICV.
Yellow is air passing up the boot, through the brake booster hoses, and in behind the throttle body.

So obviously air was getting in, unmetered, causing the idle to shoot up. Such a simple mistake to make, but at least I've found it.

As a note, the injectors are spot on, and the various other sensors seem okay, although I want to do some more electrical tests.

Anyway, with the idle now at an acceptable level, we noticed that when the throttle was opened, there was some hesitation and slight misfiring, certainly didn't sound good. So we took the spark plugs out, and they looked like this:

Untitled by Eddie the Kid, on Flickr

So yeah, pretty disgusting, so I've already ordered some replacements in the form of some NGK's, which are recommended.

Hopefully that will get things sorted.

New spark plugs arrived today, so got them fitted, old on the left, new NGK's on the right:



Slightly different fitting on the connector, but it seems to be fine. Idles well and revs up as it should.

Slight issue with the idle dropping lower than normal when I drop the throttle all the way off. Idle drops down and coughs a touch, then comes back to normal idle. I'm sure I've read about this somewhere before, so it should hopefully be a straightforward fix.

Also went up to Topgear in Stockport to collect my new Y-pipe. This will collect the gases from the two 1.5" downpipes into one 2" pipe that will head off to the backbox.





Plenty to be cracking on with over the next few days and this weekend.

Right, the exhaust is on now. It's blowing slightly, but it's on. Firstly, it sounds immense! Such a lovely noise, it's maybe a bit louder than I would like, but I'll run with it for now.

Firstly, cooling system. I need to get it bled properly. Problem is, I don't have any bleed screws or anything so I'll have to bleed it through the expansion tank, something I'm not massively familiar with so I need to figure that out.

I'm worried (I like to worry) about the temperature of the coolant. The gauge is saying it's fine, but it's a 38 year old gauge and frankly I'm not sure I trust it. I need an aftermarket temperature gauge really, something I can fit and it can give me a readout in the car, and I'll just tuck the new gauge away somewhere nice and hidden. I'm open to suggestions for this though.

Next up, with the throttle open and the revs high, there's a fair bit of blue and black smoke, although mainly blue. So it's burning oil. I did a compression test and got the following:

Cyl 1: 148
Cyl 2: 142
Cyl 3: 152
Cyl 4: 155
Cyl 5: 148
Cyl 6: 162

So they seem "okay". That was on a warm engine, with the throttle closed, and all spark plugs removed. I've not done a wet test to compare, so I can't completely eliminate the piston rings. Might well be valve stem seals, it also might just be because it's not been used in a long time, and it just kicking old oil out, I don't know at the moment.

It's very close to being driveable though, when it is, I'll be taking it to an exhuast shop as it 100% needs something better making than my attempt.

Valve stem seals would be my guess as well. Rest looks good!

So the time has come to button the car back up.

Engine wise, I'm happy. Coolant system needs a bleed, and I probably should replace the 'blue plug' (coolant temp sensor for the ECU) but that's it.

So yesterday I got loads done, it looks like a car again!





I really love how the engine sits in the bay, looks so at home and I think it really suits the car, appearance wise.

that looks beautiful man,a real credit to you

very neat and tidy, your car looks new!

drool once again!

Looks amazing!