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****************** I posted the following on Aug 22, ****************
I'm looking for some expertise/experience in diagnosing what's causing my daughter's 1988 900S with A/T nad 220k miles to run poorly. Unfortunately it's a bit hard to describe the symptoms. It starts fine cold and hot. When you "goose" the throttle in neutral, the engine accelerates like it's missing on a cylinder., but smooths out at steady rpm. Gets better as engine warms up. In gear and taking off from a stand still, the engine misses on a cylinder or two. Daughter says it "chugs".
So far here's what I've looked at and done...w/o improvement. Installed new plugs, plug wires, and rotor, altho they all looked/measured good (except as noted below). Fuel pressure ok. Fuel injectors look as clean as new. Fuel injectors "click" and resistance correct and voltage to injectors is correct and increases with rpm and opening throttle quickly. Injector o-rings replaced. Spark appears strong. Signal from Hall sensor to EZK control module correct. Engine temp sensor reading correctly both at sensor and at LH ECU.. No vacuum leaks at hoses. O2 sensor giving proper output signal. Air mass meter "burn off" cycle operating. Compression pressure was 170-200. Timing chain tight and came in proper time.
I only found two questionable things...the plugs in cylinders 3&4 seem a bit cleaner than 1&2. The ignition timing at idle was 9 instead of the 14 it should have been and the advance seemed erratic. I reset the timing to 14, but this didn't help the erratic running. As a result of the timing being off I replaced the EZK control module with another used one...no help.
********** Here's a follow-up, which I hope will be helpful***************
The car continued to run poorly...until today (10/03/02)!!! After writing the above post I tried a rebuilt air massflow meter and used engine control module...neither made any significant improvement. I also was finally able to find the connector that allow you to read off any diagnostic error codes using the Check Engine light. Error code # 12111 showed up...O2 sensor self-compensating circuit problem (incorrect air/fuel ratio whil driving). That didn't seem to be of much help, as the O2 sensor seemed to be working and there were no apparent vacuum or fuel leaks). Finally I decided it was time to take it to a dealer to see if their experience might be able to better identify the problem and/or they could hook up the car to an ocilliscope and maybe determine which cylinder was the weak one. Well...ocilliscopes are apparently "old tech" and all theirs had been scrapped! But they did think that one cyclinder was missfiring when cold and could be due to a bad injector, but they didn't know which one (all "clicked" and all had the corect resistance and voltage to them). Another possibility could be carboned up intake valves causing rough running when cold. They suggested trying a bottle of fuel system cleaner (which Id tried before) and/or obtaining a "good" injector and using it to replace the old injectors one at a time until the bad one found. So...I ran three bottles of fuel system cleaner thru the car...no help. In the mean time I obtained 2 used injectors. Installed them today in place of the old ones in cylinders 3&4....and now the car runs fine!!!!! :) :)
Not sure which one (or both) was bad...and at this point I don't care, just glad it's running good again!
Incidently, when you pull the injectors out of the manifold, you can use a flashlight to look down at the intake valves to see if they are badly carboned up. These didn't appear bad, but one valve in each cylinder (why only one?) had some deposits of a soft, shiney variety. I used a long thin screwdriver to remove a bit off one valve in cylinder 3. I don't hink this was the cure of the poor running, but....
posted by 64.12.96...
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