Engine not firing

F

flowmaster

Registered
Recent repair history: My '97 Mark III with 282K needed new rear air bags & shocks and since the fuel pump was original I decided it was a good time to do that repair also. I knocked those repairs out and discovered from reading the service manuals that the doors must be closed in order for the air compressor to engage (after 30 sec.) to inflate and to seat the new rear air bags (loud normal pop occurs). Once that was taken care I then proceeded to figure why the the car was not starting. I then realized the IFS (inertia fuel switch) might be tripped since I had the rear of the car still up in the air, once the car was lowered it fired right up and I took it for a 10 minute spin with the car performing perfectly. I then decided to go all out with rear end work and change the differential oil but I forgot to kill the air suspension switch in the trunk before I raised the rear end like I normally do. Once the oil was changed and I lowered the car and tried to start it - it would not fire up.! the starter turns the engine over fine - just does not run ... really odd.

1. I then confirmed I had no spark by spraying a few shots of starting fluid direct into the throttle body with not even a misfire on any of the cylinders.
2. Confirmed the new fuel pump was still working fine even though I could hear it engage by removing the pressure from the fuel rail shredder valve and seeing it re pressured up after a start attempt.
3. Confirmed the IFS switch in the trunk, red was fully repressed - did not move down a bit, manual says it only travels 2mm in stroke - it was firmly down ready to pop up, so it must not have tripped it.
4. Removed the negative side of the battery for a few minutes thinking it would reset the PCM (Powertrain Control Module) - no change.
5. Replaced all (8) coil packs at spark plugs about 20 months ago.

Any ideas.....?? This one has got me scratching.

Thanks,

Michael
Duluth GA
 
The most common cause for a 'no-spark' condition is usually the crank sensor. A lot of people have success simply unplugging the crank sensor and replugging it back to the harness establishing a connection.
 
JP,

I will give unplugging and inspecting the CKP ( Crankshaft Position Sensor) a try - thats the sensor that you must loosed the A/C compressor to get to, I remember now. I replaced it and the CMP ( Camshaft Position Sensor) behind the power steering reservoir about 20 months ago. The service manuals do not get too deep into the what those sensors do, but I found some interesting stuff on them. It appears the CMP enables a defined sharper dwell timing for the PCM to provide the correct voltage to the coils. The PCM uses a default value if the CMP is not functioning at the cost of poorer gas mileage. Before the repairs the engine would never start with the first try of the starter, always fired up on the second attempt. Maybe I have a bad CMP also. The engine must see a crankshaft signal from the CKP or it is totally lost as to when to provide a spark.

Thanks,
Michael
Duluth GA
 
A no-start condition with spark is going to be either the crank pos sensor or a bad PCM. If you checked the no-start condition by spraying some starting fluid into the TB, you didn't have to verify the fuel pump working or the cut-off switch being popped because you already supplied the fuel.

One was to check the PCM is to make sure your CE light comes on when you turn the key to the ON position.

If you have already replaced the crank sensor, then it could just be corroded, which is the most common no-start cause on the Marks. The pins get corroded and loose contact with the plug so the PCM doesn't get enough signal to think you're turning over the engine.

Best bet is to unplug/plug it in a bunch of times, this will scrape clean the pins and terminals.
 
The purpose of the Camshaft sensor is to provide synchronization for the fuel injection and coils on intial start up.
 
flowmaster said:
The PCM uses a default value if the CMP is not functioning at the cost of poorer gas mileage.
Click to expand...

The Cam Position Sensor is responsible for fuel injector timing.

Roadboss said:
The purpose of the Camshaft sensor is to provide synchronization for the fuel injection and coils on intial start up.
Click to expand...

The way it was explained to me was without the Camshaft sensor signal, the PCM literally guesses the firing of the injectors. As a matter of fact, as you pointed out, once running, the cam position sensor signal is not needed.
 
Wow this thread was very helpful. Never know when sommins gunna go wrong. 25 min before i had to be at work and my mark wouldnt start. hopped on the LOD and read this real quick, grabbed my chiltons book for a pic and was off in a jiffy! Thanks
 
S.o.S. same problem!!!!!!

S.o.S. same problem!!!!!!

I have the same problem.. i bought the car in tampa. i went picked it up. put a fuel system cleaner & filled up the tank. Drove it to miami with no stops. drove it around miami for the rest of the evening & it had a lil hesistation in WOT.. Then next morning I started the car. it cranked right up. I went inside for a second & when i came back outside the car had turned off. It hasn't started since. I immeadiatly thought fuel. So I went to valve on the fuel rail & it had noo preasure.. so dropped the tank, pulled the pump, they said the pump only had 22lbs of preasure. bought & installed new pump & preasure sensor on tank.. Then noticed on the message board it read; Eng. temp. data err., Rpm data err., fuel data err., trac. err.. so i connected code scanner & it will not connect to the pcm.. I checked the relay like frankie suggested I got 2 females that lite up with the key on. Swapped relay & still nothing... Now What???? PLEASE HELP!!!!!! :(
 
No firing update....

JP,

I purchased both a new Crankshaft position and Cam position sensor to tackle the no firing issue. Installed the new Crankshaft sensor first and it fired right up. Thanks for the direction there..... One note to all in removing the crankshaft sensor, be sure to remove the connector first off of the sensor before removing the 3 bolts that secure the AC compressor. Not much extra length in the wiring harness to the sensor and the weight of the compressor can stress the wires that connect into the female side (harness side) of the clip once the compressor is free.
I am glad it was not the PCM ... that would be some $$$ there.. Sensors are relatively cheap.


Michael
Duluth GA
 
Great! Didn't you try the easy fix first by unplugging and plugging it back in a couple times? The sensor was only 20 months old and should still be good as new!
 
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