car died on freeway, now wont start

[RagtopE30]

P.S. if you decided to drive the car with the relay jumped remember to unplug the wires going to 30 when you park or you will kill your battery or worse.

[Reeves]

Awesome thanks. why can I only bypass the main relay for a short time though? Am I in danger of frying something?

[jlevie]

The only caution about jumpering the main relay is that, as RagtopE30 says, you'll have to install the jumper when you start the car and disconnect it when you want to shut off the engine.

If a jumper on the main relay allows the the engine to start and run and if a new (and correct) relay is in place, the next thing to check will be to see if power is present at DME pin 27 with the ignition is on. That is the START input to the DME and is what tells the DME to close the main relay. Usually if there is no power at the START input the coil won't have power either and both are on the same circuit.

[Reeves]

Thanks a lot, I'm pretty confident I can figure this thing out now.

To clarify, if the main relay is not working, there will be no power to the fuel pump relay regardless of whether or not it is jumped?

And I'm assuming when checking dme pin 27 it is with the ecu unplugged? (Dme is the ecu, correct?) What would it mean if it had no power?

[RagtopE30]

Jumping the main relay is a temp. fix. The relay acts as the weakest link, much like a fuse. So if you use the jumper long term there is no weakest link. Relay=cheap, DME=$, ICV=$, Fuel pump=$ etc... I recommend not using the jumper for daily driving and only as a diagnostic tool.

I think what jlevie is saying is, if you jumped the main relay and the car starts then you replace the main relay but the car doesnt start again. You would need to check for power at pin 27 at the DME(ecu) with the key in on position. This will tell you if you are getting a signal from the ignition switch. But it is more likely that the main relay went bad, once again it is the weakest link.

[jlevie]

To clarify, if the main relay is not working, there will be no power to the fuel pump relay regardless of whether or not it is jumped?

Correct. if the main relay doesn't close, no power will be provided to the fuel pump relay.

And I'm assuming when checking dme pin 27 it is with the ecu unplugged? (Dme is the ecu, correct?) What would it mean if it had no power?

The easiest way to check pin 27 is with the DME disconnected. Unless there is damage to the engine wiring harness, it will suffice to check for power at the coil positive. If there is no power there, there won't be any at pin 27. If pin 27 isn't powered, the DME will not command the main relay to close.

[RagtopE30]

When I bought my cabrio the PO couldnt get it to start. It would crank and all the lights would come on, everything looked normal from the drivers seat. No power to the fuel pump or the coil. After troubleshooting the problem I found I had no power to pin 18. The cabrio has the front mounted battery and the constant hot to the DME had corroded at the terminal. These no start issues can be a pain, but fortunately they are fixable.

[Reeves]

Went to the junkyard and picked up 3 main relays, a fuel pump relay and a feeder pump.. with the main relay in I can hear the icv buzzing like crazy, and with it disconnected I can't hear it buzz at all; so I'm thinking the main is working fine as well as the dme.. but I still am not getting power to the pumps even if I bypass the fuel pump relay..

Ideas?

[r3d e30]

I am having a similar problem, but my seems to be cause by too much fuel being dumped into the cylinders. What could cause that. I did the test in the bentley's but it just confirmed that I am getting fuel.

[Reeves]

Well it turned out my problem was the crank position sensor. Back up and running now

[tjmonsen5]

im having the same problem. I am getting 1-1.5 volts at pin 30 of the fuel pump relay. Does power flow through the CPS before it hits the pin 30?

[matt0300]

if your cps is bad your not going to get fuel or spark.

[1fastETA]

Check the sensors that are under the intake manifold. They are for the tranny! I hav had the same problem and I figured it out this morning! I had checked everything else, both fuel pumps replaced, all hoses, relays, new spark plug wires, fuel pressure regulators, cleaned out fuel rail, and injectors and fusible link. Check these out, and good luck!!