Strange No Start Issue - Please Help
 

When I try to start the car the engine turns over, but i don't get fuel or spark. Randomly a couple of weeks ago when I was trying to troubleshoot this issue I accidentally bumped one of the CAS connectors with my hand. When I bumped this CAS connector the engine started trying to turn over, also the fuel injectors and sparkplugs started firing. This was all happening with me under the hood not actively trying to start the vehicle. I did notice that the key has to be in the on position for this to happen. I put my volt meter on the CAS connectors and they are both reading around 4 - 5 volts each. When I wiggle either of these CAS connectors with the key in the on position all the injectors start firing, sparkplugs start firing, and the starter attempts to turn the engine over. The FD is running a Power-FC and the engine harness was replaced with a rywire harness a while ago.

So, the key is off or out of the ignition, you bumped the CAS wiring in front of the engine and the motor started to turn over with the starter?

If so you've got something WAY goofy with your electrical system. Most likely the wheels chewed up the front fender liner and ate into the wiring harness above or some other big time harness failure.

Dale

The key has to be in the ignition and in the on position for it to occur. I will start checking that area though, I had to replace the fender liner on the drivers side because it was worn through. I didn't see any damage to the harness, but I could have missed it.

I checked the wiring harness in the fender and it doesn't have any damage. I did notice that the egi relay clicks on when I move the crank angle sensor connectors, and that is when the coils start firing, fuel injectors click, and engine tries to turn over. Key has to be in the "On" position for this to occur. Any help is greatly appreciated.

^My suggestion, do NOT get a rewire engine harness. Details in my build thread. Ray Crowe sells a brand new OEM Mazda engine harness for about $850--- the price hasn't increased in many years amazingly. If you want/need aftermarket or modified, I've heard many good things about Chris Ludwig at LMS-EFI.

Big Bad Ray can be reached via email at Crowe.Ray@aol.com or (703) 785-5554 :bubrub:

How many miles are on your chassis? Assuming your harness is original it may be time to change it out, especially with issues like you describe popping up.

I recently worked on a very nice 30k-jsh mile chassis and had the block stripped almost completely down in the engine bay so that you could see the top of the block. That harness didn't get replaced but it was pretty far from 'like new' even with such low miles.

People forget that these car were essentially rolling ovens as delivered from Mazda and most original owners didn't know any better--- kept the factory pre-cat installed and hood closed after driving. All of the under hood plastic, rubber, and wiring is predictably in sad shape in 2018.

I'm actually running a new RyWire engine harness. Could that be the problem?

Anyone have any other ideas of things I can trace down. The engine harness is new (rywire), all the connections seem solid. I feel like it is something simple, just can't put my finger on it.

Someone suggested that I log whether I am getting an RPM reading or not. I checked that yesterday and I am not getting an RPM reading (well I do when I wiggle the CAS wires, you can see it in the attached logs).

First log (1954) is me cranking it over with the key.
Second log (1957) is me wiggling the CAS wires (not trying to crank it, just moving wires).

There's either something broken with the two crank angle sensors or the wiring to them. Time to check that out.

As stated, there are a lot of issues with those Rywire harnesses, that could be most of your problem right there.

Dale

https://cimg5.ibsrv.net/gimg/www.rx7...08d210ce3f.jpg
https://cimg6.ibsrv.net/gimg/www.rx7...37f6612133.jpg
Yeah I'm thinking you're right. Shielding wire was above the cut, I had to pull the shielding back to find the cut (bottom pic). Then as I was fixing that cut I found another cut on the second wire (top pic).

D4rw1n,

Wow! Great find. Do you know what caused those cuts to the inner wires? Was the wire bundle able to swing to and fro? Will you also repair the shield?

Cheers,
George

This harness is only like a couple years old, and has zero miles on it. So this damage is directly from rywire, I am tempted to contact the company but I doubt he would do anything since it has been so long from when I purchased it. Also not sure I would want a replacement from this company anyway, guess I will start saving up for another OEM harness. Not sure what you mean by repairing the shielding, I put some heat shrink tubing (the kind with glue) on each of the cut wires. Then I pulled the raychem back up around the wires and put heat shrink tubing (also with glue) over the whole repair. Should the shielding wire be attached in some way to the other two wires?

D4r1in,

The crank angle sensor wires are shielded to keep the signal from these sensors isolated from the ignition system. An improperly shielded wire may result in that interference and may cause problems with your engine. It would be analogous to messing with your heart's electrical impulses when you get shocked. That little zap may throw your heart's timing out of whack.

Take a look at the Wiring Diagram Manual (WDM), Pg Z-34, Diagram B-1d. The far left section of the schematic shows the crank angle sensors with a shield wire tied to ground. The shield should run along that length of cable from the sensor connector to the rest of the Emissions Harness. It really shows these wires insulated all the way into the ECU, at Connector B1-01.

I was going to suggest using heat shrink tube (without adhesive) around the exposed inner wires. This would keep the inner conductor isolated from the shield. Next, the shield wire can be repaired. You can find shield wire wrap either online or at a local electronics shop (if you have one nearby). You could also search for "how to splice shielded wire". You would need to extend the wrap from the damaged area to a good area. Lastly, you could use heat shrink over the repaired shield to isolate and protect it from the environment. Would you be able to remove that glued-in heat shrink?

You should treat a broken shield is like a broken wire. It can be spliced together. Please do not replace the broken segment of shield with standard wire. That would electrically be the same because any voltage in the shield would flow to ground. However, the purpose of the shield is to protect the wires inside from any outside interference. The adhesive heat shrink you used would also not afford the same electrical properties as a proper shield. It does protect the wires from the elements but not against electromagnetic interference!

Does this better explain the reason to repair a shielded wire?

Cheers,
George

Not exactly sure where it would have been grounded before, unless that is what the cut in the plain white (no stripe) wire was for. All I did was cut a small slit in the raychem and peel it back, and then a small slit in the white sleeving to gain more room for the repair. The only spot it could have been making a connection was on that plain white wire that is cut, unless it is connected further down the harness somewhere. I may shoot rywire an email to clarify.

I emailed rywire and they told me that the shielding is grounded on the ecu side and that the wires shouldn't be cut like I found. So I guess I need to test continuity between the shielding and a ground location?

Also when I pulled back the raychem the shield wire was already exposed above the white insulator. I tried to cut down the shield wire as close to the white insulator as possible. Do you think it would be possible to put the shielded cable wrap around that repaired area and add another piece of heat shrink? As far as I know it is pretty difficult to remove heat shrink with adhesive, but I have never really tried.

D4rwi1,

Please inspect/measure resistance on the CAS wire harness to check for any other breaks.

A shield from shielded wire would normally make contact with the shell of a connector or would feed into a pin on the same connector. Based upon the schematic, the outer shield does not feed into a pin on any connector. The shield is connected to ground at Ground Point #5. That ground point is located in the cabin, next to the ECU. What do the connectors look like from your Crank Angle Sensors?

If I was to repair this wire harness, I would:
1. Insert heat shrink on the inner wire around the cut.
--Do not use a small lighter. Use a heat gun; see if a buddy has one, Harbor Freight sells one for pretty cheap. I paid $8 for it on sale. A hair dryer on high heat may also do the trick.
--Alternately, you could use liquid electrical tape so long as it is applied all around the exposed wire. However, heat shrink is the preferred method to isolate and protect the wire.

2. Insert a larger diameter heat shrink over wire harness.
--Check for proper length first.
--It may be necessary to slide this heat shrink further down the wire harness to account for the CAS connector.
--If the pins are removed from the CAS connector, as seen in 2nd photo then this heat shrink could be applied last.
--The length should cover the repaired shield, including the amount that was peeled back.

3. Cut back enough insulation, approx 1-2", to reveal the outer shield.

4. Use shield wrap around the exposed inner wire to replace the missing segment up to the CAS connector(s).

5. The shield wrap may need to be soldered to the old shield to provide an electrical and mechanical bond.
--Be careful not to melt the insulation from the inner wires.

6. Apply heat to heat shrink tube over the repaired wire harness.

7. Check each wire for isolation between one another with a DMM.

Cheers,
George

The repair is really close to the connector. Also the insulation that is around the shielding is just insulation, it doesn't appear to be connected to the wire in any conductive way. You can see the inside of the shielding insulation in the other pics. It's the white insulation.https://cimg0.ibsrv.net/gimg/www.rx7...317762ca87.jpg