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Discussion Starter #1
My Elantra all of a sudden refuses to start using the starter/ignition key. It only cranks and backfires, but don't want to start. When I get my two sons to push the vehicle it starts very easy not even pushing further than about 5 meter and releasing the clutch in second gear. After that when I stop the engine and immediately try to start again, the same happen again - cranking and backfiring

I already replaced the Plug wires, Plugs, Petrol filter and Camshaft position sensor (a lot of users on this forums point to hagin problems with the CPS) and timing belt. When I disconect the fuel line, and switch the ignition on a lot of fuel is pumping out of the filter, which rules the fuel pump out a possible culprit

Any other ideas where I can look at ? >:D
 

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Since your problem only happens when the starter motor is operating, I'd first carry out a voltage drop test on the engine ground wiring.
Connect your voltmeter black lead to the battery negative terminal and the red lead to the engine block. Monitor the voltage during crank and make sure your reading is less than 0.5V.

If that checks OK, next connect the red lead to the ground wires on the back of the engine below the intake mainfold. Connect directly to the wiring, not the bolt. Crank the engine again and confirm there is less than 0.5V again. If any of the voltage tests show a voltage higher than 0.5 volts there is a high resistance in the wiring.

Scottie.
 

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Discussion Starter #3
Hi Scottie
Test 1 is ok - I'm getting 0.45V between the engine block and the battery Negative when the engine is cranking
On Test 2, do I need to remove the wires from the bolt and just test between the wires and the Battery negative ? If this is correct there might be a problem because I'm getting 4.7V when the engine is cranking. When I put the wires back and attach them again using the bolt, I'm also getting between the wires/bolt and the battery negative, just under 0.5 V
Wicus
 

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Sorry, I didn't make that clear.

You want to have the wires still bolted to the engine but you need to connect the meter to the wires themselves not the securing bolt.

If those tests are OK, I'd next measure the voltage between the battery neg and the car body, looking for less than 0.5V again during crank and if that test is also OK then I'd test between battery neg and the ground wires right at the engine computer. It's OK to extend one of the meter leads using some wire if it wont reach.

The computer should be in the driver's footwell behind the dashboard. The ECM grounds are on terminals 2,3 & 31 (see attached). You want to have the connector plugged into the computer, so back probe the black wires and check voltages during engine crank. You'll need to remove the cover off the back of the connector to access the wires.

Scott.
 

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Discussion Starter #5
Thank you Scott - will test this tonight and let you know. Seeing that tests are going in the direction of the ECM, will this still be valid keeping in mind that when I push start the vehicle it starts without a problem and allow me then to drive around like normal, as long as I don't stop the engine and try to start it again.

Are there some components in the ECM which only operate when cranking the vehicle ?
 

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Are there some components in the ECM which only operate when cranking the vehicle ?
No, but my thinking is the high electrical load of the starter motor operating is having an effect on the engine ECM ground circuit. My thinking is often totally wrong though :) but it seems a logical place to start. Especially when the ECM on your engine is grounded directly onto the engine block.

Before you go dismantling the ECM connector, if you have jump leads it might be a good idea to try jumping the battery neg terminal to the engine block as a quick & dirty test. Your engine ground only just passed the voltsdrop test. I would normally expect to see the engine ground circuit have a voltsdrop of about half what your is.

Scottie.
 

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Discussion Starter #7
Hi Scottie

I tested the earths on the ECM which was exactly the same as the tests I did on the Engine Block. As a last resort I replaced the Crankshaft Censor, which resolved my problem. Car is starting without any problems. I swopped it back with the old one, and it refuses to start and also backfires like mad.

I've tested both the Crankshaft sensors and they give exactly the same readings between the three pins. The one that was installed in the vehicle is a "pirate part" according to Hyundai, because they claim to never have come out of the factory like that (Images uploaded). The one with the metal housing is the faulty one I replaced with the "plastic only" unit. I bought this vehicle new in 1996, and at those day we only got 1 year guarantee, and from there onwards I did all the services myself. Weird

At least it's going again now, with the Crankshaft censor being the culprit. (It seems that the car can be push-started without these censors working)

Thanx for all the assistance
 

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Wicus, I'm glad you got to the bottom of your strange non start.

WOW..I would never have guessed a crank sensor could cause your engines symptoms.
Every days a school day in my job :) That's what makes it so interesting.
I'll file that fix away for next time. Thanks for posting back in and sharing the outcome.

Regards.

Scott.
 

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hi Wicus, I had the same problem with my 96 Lantra, it would not start when hot but would when cold and being auto I did not have the option of push starting. While waiting a couple of days for a crankshaft sensor to arrive I poured about a litre of cold water over it (the crankshaft sensor) before attempting to start it when hot and it started every time. They tell me the crankshaft sensor fires it up and the camshaft sensor keeps it running , I don't know how much truth there is in that, but once the crankshaft one was replaced it was all good again.
 

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When they fail, the crank sensors tend to go open-circuit when hot. Hence they read fine when cold but cause the engine to randomly cut out as it warms up.
 
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