mx5cartalk.com

Okay I've suddenly joined the ranks of frustrated MX5 owners but maybe its something simple. The car (NA1.60 last week ran perfectly to the shops. When I came out 10 mins later it would not start - ticked over and gave one kick. After waiting five mins finally got it going. Later in the day it did it again but this time fuel guage showed empty! I put some
fuel in and got it going again. Suddenly the tank was half full so it was not a senior's moment and I had'nt run out of fuel. I replaced the main relay and its run well until this morning when it coughed twice a kay from home and now is parked in my driveway but wont start again. The fuel guage is not working even though it has plenty of fuel. There must be a connection between the two ie when the gauge is working the car is good. I've poured cold water on the cam angle sensor to no efect. Any views on this one?

I got total not starting issue form a dead main relay, but that would not explain the coughs..


You'll get your torque wrench back soon too, got the motor sitting in the car now :> (no wires, hoses or engine mount bolts!)

There are a LOT of NAs dying due to electrical problems. They must be at that age when things just start to fail.

Thanks Andrew no rush unless I use the wrench to bash the hell out of the fuel tank. Am about to see if there is any fuel in the system.

Disconnected the fuel hoses no fuel under pressure nor pumping thru when engine turned over - guess that doesnt necessarily mean pump is stuffed.

Check out the wiring diagram. I recall there was a circuit opening relay (or something like that name) that kept the fuel pump running until there was airflow after start. IIRC, it was powered via a wire from the AFM. The wire may be dislodged, the relay may have died or you have lost power to that system.

trader wrote:Thanks Andrew no rush unless I use the wrench to bash the hell out of the fuel tank. Am about to see if there is any fuel in the system.

LOL! Thanks

I think a sledgehammer would do the job better though!


Agreed with earlier poster, check all fuses and relays related to fuel. Perhaps check connections to ECU? (long shot!)

Might be the Igniion switch

An electrical problem will normally mean the engine cuts immediately, eg if the CAS fails then it's dead straight away. If it's 'coughing' then I'd be looking at fuel starvation. On such an old car the FPR normally weakens and can't hold much or any pressure. Simple to check, just clamp the return line (not completely closed) and see if that makes a difference.

HTH
Phil

To check fuel pump works:

Bridge GND-F/P in the diagnostics box
Turn ignition to on
Check for fuel pressure.

Tried to start it this afternoon. Dead as a dodo. Disconnected the fuel pump and checked power. Had power, reconnected it and low and behold it started, fuel gauge worked as well. Now looking afm and electrics but unfortunately while it is going it is difficult to track down.

Maybe you have a dodgy plug at the tank? The gauge and pump use the same plug dont they?

The symptons sound different to the normal Circuit Open Relay issues. Generally the COR issues stop the pump from running, but the fuel gauge is not affected. As Garry suggested the plug at the fuel pump might be dodgy? Might be worthwhile giving the contacts a clean.

Let us know how you are going.

There is heaps on info on the big forum about fuel pump and COR issues, to the point of brain overload.

J

Yes, the COR looks like not being the problem.

Just had a look at some wiring diagrams for the 1600 model I still have on disk.

There are two different wires for the fuel gauge sender and the fuel pump. The sender has a yellow wire in and a black earth. The fuel pump has a blue/red in and a black earth. However, the blue/red gets its power from the COR which in turn gets power via the main relay. See attached.

Thanks for that JBT - good to know what the colours mean. Just put a light on yellow and earth and had power. None on the blue/red/earth but realised I had to turn the motor over. When I did that I had power. Put the plug back and it started! Problem not resolved and need to have it stop working to do some more checks.

Dont know if the AFM switch could have something to do with it but cant get to the contacts anyway.