ECU code 9 cam drive problem

Third Generation Honda Prelude topics

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Randal58
Prelude Enthusiast
Posts: 4
Joined: Fri Mar 14, 2014 10:55 pm
Prelude Model: None, regrettably
Location: Tasmania, Australia

ECU code 9 cam drive problem

Postby Randal58 » Sat Mar 15, 2014 12:25 am

I bought a cheap 1988 Si 4WS about a year ago and dealt quickly enough with the oil leaks, but I was left with the problem of severe bogging below 3000 rpm when the engine was warm. The fact that it ran well when cold gave me some confidence in the general condition of the engine and a compression test came up OK. Anyway, it took me months to get to the bottom of the problem, and having now fixed it I thought I'd report it in case anyone else encounters something similar on high-mileage engines.

The code 9 (cylinder sensor) appears to set when there is less than about 340 degrees (in crankshaft terms) between the CYL pulse and the TDC pulse from the distributor. That should pick up one of the camshaft pulleys being one tooth out on the belt, but that was not the issue here. I found that when i went to set the ignition timing, it would drift further and further retarded until I ran out of travel in the adjustment slots of the distributor. Being new to fuel injection systems I blamed this on the ECU and spent ages looking for faulty inputs, but to cut to the chase, it turned out to be a purely mechanical problem: the intake camshaft pulley was loose on its shaft, and the Woodruff key was flogging out the slots in the pulley and shaft. There was a good 15 degrees of play, which is 30 degrees at the crankshaft. So the main effect was to retard the ignition, but it may also be that the inlet valves were lagging with respect to the injection pulse, which i believe is triggered by the CYL sensor on the exhaust camshaft.

Now you may wonder why it was not obvious that the camshaft pulley bolt was loose, assuming that was the root of the problem. It actually took a fair effort to release the bolt. It seems that the head of the bolt was stationary with respect to the pulley and the camshaft was jerking back and forth on the thread of the bolt. With the threads being fairly dry, the resultant galling prevented the bolt from unscrewing.

This is obviously a rare problem, since a Google search didn't show up any other mentions of it. On the other hand I did come across one or two mentions of symptoms very close to mine, and it could account for obscure drivability issues in less extreme cases. The main giveaway would be the appearance of brown metallic dust on the back of the pulley (from fretting between the pulley and the camshaft) and it might also be detectable by putting a large shifter on the 26mm hex part-way along the camshaft and looking for play between the pulley and the shaft.

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spiffyguido
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Re: ECU code 9 cam drive problem

Postby spiffyguido » Tue Mar 18, 2014 9:09 am

Wow. Really great information!

Thanks for coming here to share. No doubt someone will benefit from the issue. It certainly sounds like you went all out to find the source of the problem.

Randal58
Prelude Enthusiast
Posts: 4
Joined: Fri Mar 14, 2014 10:55 pm
Prelude Model: None, regrettably
Location: Tasmania, Australia

Re: ECU code 9 cam drive problem

Postby Randal58 » Tue Mar 18, 2014 7:40 pm

Actually I have to confess that I took the car to a garage in the end. This was a blow to my pride as I had not been to a mechanic for about twenty years before that. Anyway, they had the car for about three weeks and then I had to fork out another $70 to get it towed home, so the diagnosis cost me more than the car itself! But then I picked up a second-hand camshaft and pulley that afternoon for $40 and it was running sweetly the next day, so I am happy with the result.

All this points to the value of a forum such as this. With the cars being 25 years old there are plenty of cheap parts around, but the lack of a diagnosis can knock a thousand dollars off the value of a car. Using the pooled experience of fellow enthusiasts we can swoop on these bargains and come out in front.




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