Another wierd one today.

nickb2

Wrench. Diagnostic Tech.
Joined
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Location
St-Hyacinthe, Quebec, Canada
#1
Make
mazda
Model
miata mx5
Year
1999
Miles
190ish k km`s
Engine
1.8l
Car came on dolly by client.

Car cranks but won`t start. Client says he replace plugs, wires and even checked compression.

Put scanner to car, check for engine revolutions, scanner shows zero rpm when cranking. I check spark quality. The spark is extremely weak at only 20 kv gap. So I get way to ahead of myself, check secodary on coils, they check fine, check primary, checks fine. Check for proper routing of wires and firiing order as I did not install these wires. They are good and properly installed. Check compression myself, 200ish on all cyl.

Next, I check gap for crank sensor, adjust it to 0.5mm. Still have weak spark. Very weak. White pale color. SO I get again ahead of myself, call for a crank sensor. It get to the shop, I have high hopes as Mitchel and alldata both say that if scanner shows no rpm, and signal and ground good to and from PCM to crank sensor harness is good, crank sensor is faulty. Well, I install the new sensor, no joy.

Next, I focus on what I should have done from the start, air spark AND fuel.

Hook up fuel pressure tester, zero pressure, check fuses and wiring, find no fuel pump relay activation clicking. I bypass relay, 60psi before regulator. Attemp to start car with fuel pump bypassed, sputters and dies. Check spark again, now it is bright blue orange and you can hear it snap. So it was a good call on the crank sensor, but something is still eluding me. Since I have the fuel filter close, I remove it, pour some gas out of it, nothing gooey pr finky, but notice it doesn`t smell right. Smells like alcohol, not that octane smell.

So I decide to do a test, cross the parking lot and put a few liter of 87 in a jug. Take out my fuel pressure injector cleaner kit. Pour in gas to my cleaner, apply shop air to cleaner canister regulator with my fuel pump bypass undone and adjust to spec. Car starts and bucks for a few seconds than purrs like a Kitten.

So next, I check if I have signal from PCM to activate the fuel pump relay, yup, I do. Pcm grounds the relay coil. So I call for a new pump relay, won`t arrive till monday. Push the car back in the lot. But on my lunch break, I check the relay, pull cap off, notice nothing out of the ordinary. Winding has 500or so ohms, coil side, and power side, I have zero ohm when contact pushed in. So I say to myself, this relay looks good, but can it be the plunger inside the coil is stuck. But at this point, I have to eat and smoke a few cigarettes and decide to wait till monday to see how the new relay will act.

So this car had three strikes against it. Weak spark due to failing or weak crank sensor. Old gas. And a faulty fuel pump relay.

What are the odds on that one.;):bat:
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
8,833
Likes
153
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Location
St-Hyacinthe, Quebec, Canada
#2
Afterthought, scanner was probably not seeing rpms revolutions as the battery was so low it was not revving fast enough to register. I did put the smart charger on it during lunch break but did not check with scanner to see after crank sensor replacement. But for sure that spark was snapping way more than before. I am convinced I did not call that sensor for nothing.

But I do hate it when I miss a step like this. I was so focused on air and fuel, I completely forgot to check fuel.

But in this case, even when circuit and pump bypassed, still had a fuel quality issue. This was a good one for a beginner back to basics troubleshooting. The apprentice next to me kept on bugging me but I had fun with him as he is eager to learn, and this miata was very clean and nice to work on for a 1999. I will let him test drive it next week as it will need a good rinsing on the highway, if you all get my drift. These are fun little cars to splash around a few bends.