Britt Bolen

so I'm having some engine trouble...

I've got a US 928S 32V, and I can't get it to start because it keeps flooding. It appears that the something is causing the fuel injectors to just stick open and soak the cylinders and plugs with gas. Cranking it for 5 seconds fouls the plugs and soaks everything with gas.

Things that have been checked trying to find my starting problems...

compression - fine (except none when the engine is soaked with gas, normal after letting it dry out for a few days)
timing - fine
spark - fine
fuel pressure - fine

I'm guessing either 1) my fuel injection brain is fired or 2) there is a ground somewhere that is causing the injectors to stick open.

Are the injectors on this 928 the type that always have power and fuel, and open based on a ground signal from the brain?

Has anyone seen anything like this?

My current plan is to try and find a spare brain to swap in and see if that helps, in the mean time i'm going to try and look for bad connections, or faulty grounds that might be causing the problem.

thanks,

Britt

G Man

I came up with these ideas from doing a search

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The fuel goes from the tank to the injector rails and then back to the tank. The pressure regulator and dampners pressurize the fuel system. The computer opens and closes the injectors. If your injectors are staying open and filling the cylinders as you say, then the injection brain is faulty. Find another brain and test it.
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Stop. Take a deep breath and back away from the car.

There is another possibility that makes more sense. Your car has a pressure regulator and two pressure dampeners installed on the pressurized fuel rail. Each of these units has a flexible diaphragm exposed to fuel pressure on one side, and manifold vacuum on the other side.

What happens if one of those three diaphragms splits?

Yep - fuel pumped directly into the intake. Instant flooding.

If the pump is disconnected, manifold vacuum pulls fuel into the intake and the car runs (poorly).

Pull the vacuum line off of each of the three units and check for traces of fuel. Replace the one that leaks.
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Bill51sdr

Sounds like a bad LH computer. You have one of the classic symptoms, i.e. the flooding issue.

Lorenfb

The possibilites are:

1. fuel pressure too high - use a gauge to check
2. fuel being sucked into intake via the fuel pressure reg vacuum line -
remove the vacuum lines and check for fuel
3. temp sensor bad - check with an ohmmeter S/B < 3K ohms cold
4. bad LH unit (this failure mode is very rare) - use an injector test light to monitor
the injector pulse time (good vs bad running)
5. bad MAF - disconnect before cold start problem

Britt Bolen

Checked the fuel pressue, that's ok. There's no gas in the intake runners, so I think the vacuum lines are ok, and wouldn't a leak in that also affect fuel pressue? Also checked the temp sensor, that's ok...

thanks for the suggestions... still sounding like the brain... stupid computers, i hate computers.

Britt, computer programmer by day, computer hater by night

Rich9928p

Britt,

You didn't mention the year of your 928 - from the picture I'd guess '85 or '86. If correct it uses a 25 pin LH controller (different from the 1987 and newer 928s). Other suggestions are:

a. check the Temp II sensor. If the LH thinks the engine is cold, it will provide too much fuel.

If the ambient engine temperature is too warm to check the Ohm reading at colder temperatures (0C/32F), remove the Temp II sensor from the engine and immerse it in cold ice water. A failure mode of the sensor is to go open circuit (infinite resistance) at cold temperature. A cold test is necessary to confirm functionality of the temperature sensor for cold start.

To check the Temp Sensor II, you will need an ohm meter. Remove the connector to the Temp Sensor II. There are two prongs on the sensor. There are two separate temperature sensors housed in the one sensor body (in LH fuel injected 928s, one sensor is for the LH and the other for the spark module).

Note the orientation of the protruding alignment notch in the outside of the sensor. Prong 1 is the sensor for the Electronic Ignition and prong 2 is the sensor for the LH fuel injection. Clip one of the ohm meter leads to prong 2 (LH) and clip the other lead to a ground point. Do NOT connect the ohm meter leads between the two prongs of the sensor. Repeat the resistance measurements for prong 1 (Electronic Ignition). The proper Temp Sensor II resistance measurements are:

0 C / 32 F: 4.4k to 6.0k Ohms
15 - 30 C / 59 - 86 F: 1.4k to 3.6k Ohms
40 C / 104 F: 0.9 to 1.3k Ohm
60 C / 140 F: 480 to 720 Ohms
80 C / 176 F: 250 to 390 Ohm

If the resistance readings are not correct range, the temperature sensor must be replaced. If the resistance readings are in the correct range at the sensor, there could be a problem with wiring to the LH controller or the connector itself could be corroded. Measure the resistance from the Temp II sensor connector to the LH and spark controller connectors to confirm the circuit is good.

I aways suggest a quick verification of the Temp II resistance levels test at the LH connector. This verifies that the wiring is good and the connector is tight. Place the Ohm meter leads between pin 2 and 11 of the LH connector (see the diagram of the LH connector) and compare the resistance level to the measurement at the sensor. The readings should be very close (only the resistance of the wire is added).

b. check the fuel pressure regulator and pressure dampner. Failure of these itsm are very common and cause of rich running condition.

c. check the MAF. Unplug it, start the engine (may take a little pressure on the throttle). If the engine runs better, your MAF could be going bad.

d. Swap LHs and see if that helps - the LH in this car is pretty reliable so I'd go after the other items first.