1990 740 8 valve 2.4 Bosch

Car still idles great but no go when you step on the throttle. Replaced the AMM and IAC due to codes from the computer. Replaced both fuel pumps and filter.

All four spark plugs are badly carbon fouled. I am rebuilding the injectors, replacing the spark plugs this weekend. I am going to replace the distributor cap and rotor also. Maybe the coil.

I rebuild as a hobby SB Fords so I am not a total dummy. My experience tells me that the spark is too cold. What exactly does the power stage module do??? Is it an ignition module. Does it amplify the spark?

The dumb book I have does not answer these questions. Is the coil 12v or use a resistor to use less???

Thank you!!

Went connection by connection and cleaned everything. Rebuilt the injectors and cleaned the TB and PCV. Test the coil and wires. Disconnected the cat. All okay. Swapped out the power stage module with no change. But finally I am getting a code off the ECU. 214 - crank sensor. Just maybe I am getting close????

If there's no chance that the sensor wheel could have been damaged, check the wiring to/from the crank sensor and then replace the crank sensor.

If there's a yellow stripe on the crank position sensor, replace the sensor.

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alex

To answer some of the asked questions. Fuel regulator is new and I have plenty of pressure. Temp sensor OHM'ed perfect at cold and after 20 minutes.

Since then I have dropped one of the injectors and I broke the tip. How specific are these injectors to the model year??? I went to NAPA online and found the same part for both a 1990 740 normal and a 1988 740 turbo but the part numbers are different. (I pulled a couple out of the 1988 turbo in the wrecking yard.)

Any help??? Thanks

You'll need to (or you should for best results) match the part numbers. So any LH-Jetronic 2.4 turbo (90-95 740, 760, 940, 960 turbos).

Supposedly the LH 2.4 turbo injectors flow more fuel, but I've seen some posts claiming that they had their later injectors balanced and they flowed the same 300cc/min that the earlier style ones are rated at.

In a pinch, you could replace all four injectors with your old ones. The ECU should be able to compensate for any small differences there may be between the two styles.

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alex

The power stage is an amplifier that provides the coil a square wave for firing. Usually when it fails, it really fails.
Poor plug condition can result from secondary ignition problems (coil, wires, cap/rotor) or mixture.

Sounds as though your car is running rich. Any black smoke out the back? Have you tested the fuel pressure regulator per the FAQ?

The power stage can fail in weird ways, resulting in odd running. Considering its price and ease of installation, you may as well replace it.

Rich running.. also the coolant temp sensor.

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alex

The last one I did was weird. After it heated up or under hood temps are high, it would idle like crap and die frequently. I took a water hose and cooled it down and it would idle great for 10 min+. Worth a try, just to see.

Most of the time the just seem to croak all the way, though.