Cold start problems with LH-based 928s

When troubleshooting, always start with the "easy" and inexpensive items first and work your way to eliminate problems until you end up to the difficult and expensive items. The majority of electrical problems are connection related.

If the ECU doesn't know that the engine is cold, it does not provide cold start enrichment and it will not start. Eventually after cranking enough, there may be enough "raw" fuel sprayed into the intake to start the engine. You would see smoke after starting because the fuel wasn't metered properly.

The Temperature Switch II is located in the front center of the engine just to the right of the fuel pressure damper.

1. Check the plug to the sensor, is it on tight? Are the contacts clean? If not, clean the connectors and clip it on tightly. Check engine starting now. If it does, you're done. If not got to step 2.

2. To check the temperature II sensor, you'll need an ohm meter. Remove the connector from the LH control unit. Connect the ohm meter to pins 2 and 5 of the LH connector (not to the pins on the module itself). The correct value ranges are:

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

Since your problem is cold start, you could just look for the proper resistance range for the ambient temperature of the cold engine. If the sensor is shorted (zero ohms resistance) the mixture will be too lean and the engine will not start when cold. For problems at other engine temperatures, I'm including all of the resistance ranges for higher engine temperatures. If the sensor has an open circuit (infinite resistance), the fuel mixture will be too rich, the engine will not run when warm, and will be difficult to start when warm.

If the values aren't correct, measure them directly at the Temperature Sensor II. You'll see that there are two prongs on the sensor. There are two separate temperature sensors housed in the one sensor body, one for the LH and the other for the EZK module. Note the orientation of the protruding alignment notch on the outside of the sensor. If you are viewing the alignment notch orientated to the left side, the prong closest to you is the prong for the LH controller and the prong further away is for the spark control module. Clip one of the ohm meter leads to the prong closest to you (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.

If the resistance readings are in the correct range, there is a problem with wiring to the LH controller or the connector itself could be corroded. If the resistance readings are not correct range, the temperature sensor must be replaced.

If replacing the sensor doesn't fix the cold start problem, check the fuel filter, fuel line pressure, injectors etc. Fuel injectors can be removed and tested for flow and flow pattern. There are several shops that provide this service. The problem could also be attributed to bad ground connections. Also, don't overlook potential weak spark conditions. If you've eliminated all other areas, a failing LH controller could be the problem.

Rich Andrade

 

So, new Temp II in the water bridge and readings are within range.

No continuity when inserting probes into the harness end. I think that rules out shorted wires in the harness itself.

The LH works fine on my cold 88 started right up.

I guess the next step is to check continuity from the harness end to the LH and EZK harness ends.

 

Well, if I read the wiring diagram correctly, one wire from the sensor goes to the terminal 13 of the LH and the other goes to terminal 19 of the EZK

 

You are correct sir.

That's where I'm going next.

 

Cant wait to hear the result!

 

No continuity from either side of the harness to LH or EZK harness end.

 

So were you testing from the LH terminal to the EZK terminal? THat should be about 5K cold.
What about from the sensor end to the EZK and the sensor end to the LH end?

 

Temp II harness end to LH harness(13) or EZK(19) end should be continuity, right? That's what I'm testing.

 

well, one wire goes to each ECU so depending on which wire you are on, if everything is disconnected, one wire will show no continuity to one ECU and the other will show continuity nd vice versa for the other ECU.
How about if you jump the to wires together at the sensor and then test between terminals 13 and 19? They should show a dead short between those terminals and open to ground

 

Here you go.

 

46 ohms. Might just be some wiring resistance. Will it start cold yet or still a problem?
Open circuit to ground so no grounded wires?

 

No start cold without starter fluid.

 

If you plug the connector back in on the temp II sensor and then measure the resistance from 13 to 19, you should read around 5K if the engine is cold. Try that.

 

It is very important to have WSM with wiring diagram.

I was repairing the Temp II sensor and wanted to be sure the wires were right. The WSM said they were GN(LH) and GN/RD(EZK)

Well my colors did not match. I looked at the Fuel Cannister wires and they matched.

Now I understand why the shorted wire melted the connector and Temp II switch.

I'll repair both harness ends tomorrow. Bet it starts right up.

Kevin

 

That is crazy.
Are they close enough together to mix them up? Not looking under a hood right now. to see them