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Date: Sat, 20 Mar 1999 20:53:58 -0600
From: Paul Hahn <>
To: zzz bmw Mformation <> Subject: M635 rebuild - start-up


The last time we met, I was assembling the accessory equipment on the m88/3 engine. I must admit that a few comparisons to my daily driver (an identical twin) made the job easier. The next time i do an overhaul I will make copious amounts of video tape at the various stages of disassembly. The ravages of time on my 49 yr. old memory were in full evidence. The reassembly of the engine bay components took place about 10 months after the disassembly. The job isn't too demanding , I think I got it done in three sessions of 4 hours each.

So here I go - it's the big day of a virgin engine. A pre start compression check shows even at 155 lbs across the six holes. The rings haven't seated , of course, so i'm not deterred by a low reading. My gauge is probably not calibrated for accuracy either. The important thing is that the readings are about equal. I left the fuel pump relay out of it's socket so the injectors won't squirt. I removed the 12v wire from the coil so it wouldn't develop an output voltage. All spark plugs were out and the throttle plates were wide open. The air flow meter and filter assembly was waiting to go in after the test. I ran the starter for an equal number of compression strokes on each cylinder : seven strokes and the needle quit climbing each time.

I finished the ignition and fuel components and cranked the starter. - no explosion no start no pop no anything but a spinning engine. I checked for spark at the coil by connecting a spare plug to the end of the coil wire that connects to the distributor and it displayed a nice white/blue lightning bolt about six times per two revolutions of the crank - just right. I checked for spark at the number three plug wire and got good results there. I pulled a plug and it dry - no fuel, not even a hint of fuel odor. I took my volt meter to the ECU (electronic control unit - residing in a steel can above the glove box) and after removing the 35 pin connector backing and reattaching the plug to the brain , I measured the signal from pins 14 and then 15 to ground and discovered the 12vdc to the injectors was missing. You should see a steady 12vdc with the ignition switch on (all instrument lights lit) and then it will drop to about 9vdc when you crank the starter. I had no 12vdc at all , so I followed the schematic and found a loose connector above the glove box. The 12vdc power for injection comes to the main relay (attached to ECU case) on a red wire that is fastened to the cabin side of the fire wall just fore of the glove box. This same wire has a fuse link at it's other end , the POS terminal of the battery. I had experienced an intermittent "fail to run" problem a few years ago on my car and tracked it to a loose bolt on the battery cable terminator.

With proper signals now evident at the injector control points of the ECU I turned the key again and the fires were lit!! The engine missed a few times as air bubbles purged from the fuel rail and in about 35 seconds, steadied out to a smooth 1100 rpm. I set the idle down to 1000 by adjusting the large brass straight slotted screw in the intake manifold between the number 3 and 4 hole. Smoke poured off the exhaust manifold as it came up to temp. The custom forged pistons made a noticeable amount of "growl" until they warmed and expanded. The temperature of the radiator supply hose rose as the t'stat opened and i let the new engine sit there and idle for about 20 minutes. A few blips of the throttle assembly resulted in a power promising surge of engine music. I shut it down , changed the filter and oil to an all climate 20w50 petroleum product, and then went for a test drive around the neighborhood. What a TREAT. The smoothness is there , the exhaust note is deluxe. I now have 100 miles and a thousand grins behind me. I drive with some restraint , varying the engine speed and keeping the physical load on the engine to moderate levels. My self imposed rpm limit goes up every day - I've hit 5500 and make new forays as a slow and even climb of the tach. I'll check my valve clearances this weekend and change the oil/filter at about 500 miles. At 5000 miles I'll switch to a 15w50 synthetic engine oil. I've heard that breaking an engine in on synthetic can jeopardize the ring seating process.

NOW I have a bit more motivation to sell my former daily driver. It looks like the car will go for peanuts - I've been advertising for a few months and have had no offers. Anybody want a great M635CSi for under $11,000 ?? Make me an offer and get a nice surprise!! It's a 1984 black on black with a 32k mile engine and a like new suspension. This car is better than a 32,000 mile "garage queen" because the rubber and seals are only four years old instead of 15 yrs old.

Paul Hahn

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