Hi all, just been reading all the threads about crank but no start and it seems to be a common issue. Am I right in the general consensus it is more than likely either Crank Position Sensor, RCM, or Fuel Pump/Relay Issue?

My crossfire has been sitting for a while without starting (maybe 8 months) and noticed the battery was dead. Replaced the battery, but now wont start. Remote works fine, so didn't think it was a security system fault.

I don't have a merc type scan tool, just a little generic one, and shows no codes. Nothing is showing on the dash when I try to start, and I have replaced the CPS with a new bosch one I bought for the donor (eventual 5.0lts swap from my W163 ML500) which looks like it's the same part. Still no start. Also when I tried to start a couple of times, I can smell the fuel getting delivered so pretty sure the pump is working. Checked the fuses, and can't find any blown.

I haven't removed the RCM yet, or the relay, but wanted to know if there's something else I could be checking. I will check the CPS with the multimeter when I have someone else there to crank while I watch the output or remove it and check the ohms, but the only strange thing I see happen when I try to start is the light on the switch for Rear Spoiler flashes and when I replaced the battery, the spoiler raised. I know it's difficult without a scan tool, but a lot of the recommendations on here for scanners, date back to 2008.

Finally, if the CPS is sending out the correct volts (can someone tell me what should I expect from the CPS while cranking?), then should I unplug the RCM and remove and check, or is there a step between I could try? I saw a video of an slk320 not starting due to a bad Cam Position Sensor or bad connector to this. Thoughts? Oh also have the 3000+ page crossfire service manual if anyone wants it. Not sure if it's on here already.

 

Remove and open the RCM.
Reinstall.
Turn the key to the On position. The Fuel relay should close for 2 seconds when the key is first turned ON, then it will open.
The two relays shown should remain closed.
Are they?

 

There is no testing of the CPS, replace it. You will see bias voltage, but you won't see the blips as the engine turns over with any meter you can buy at Lowe's, that would take a $500 Beckman or an audio-quality oscilloscope.
I'd go with DJ's suggestion - CPSs usually fail at high temperature, then work when the engine cools down, it is not characteristic of a CPS to simply fail like that.

Do what DJ told you to do. IF the fuel pump relay closes, test for fuel pressure, you want 58psi +/- 3 psi. The engine will start on as little as 25psi, but won't run right (actually a COLD engine may not start at such low pressure). I like the OTC test kit for this, under $50 and it diagnosed my Truck when it started to act up.

The fact the starter engages narrows it down to fuel or ignition. With a car that sat that long, hard to say what you will find, but I really doubt it's the CPS. One thing you CAN do, is yank a plug cable off and see if, during cranking, the coil throws a spark, if so, the CPS is fine - the ECU will NOT fire plugs or injectors if the Crank Sensor or Cam sensor has failed. If you get a spark, those sensors are fine. Expect it to bridge only a fraction of an inch and do not hold the cable with your hands - if it is firing plugs, you will FEEL it and if you are a cardiac patient, it would be best to avoid being jolted.

https://www.summitracing.com/parts/o...RoCrdsQAvD_BwE

 

Thanks, I will check that out on Friday when I am there. I have it sorted offsite.

 

thanks pizzaguy. Yup, I was going to test spark. I can smell the fuel when I try to start a few times - like flooding so pretty sure fuel pressure if ok, but will check everything you both have suggested. Appreciate that

Does the on / off 3 times and back on (to all lights on, not actually start) with the key work on the crossfire like it does every other chrysler/dodge to display all codes on the dash? I will check that on friday if you dont know.

 

No, it's a Mercedes system, not a Chrysler system. The only Chrysler systems are the TPMS and the Occupant Restraint devices. If you have fuel, then you have ignition (or should). Now, VERY RARELY, fuse 11 blows, that is the primary power to the coil packs. It is VERY rare but that fuse has blown in the past.

 

Thanks for the reply. Yeah, I will check the spark on friday. I am thinking I am not getting spark. Checked fuse 11 when it wouldn't start. It wasn't blown, but changed it anyway. Will update tomorrow when I check the Cam Angle Sensor. Is there a fuel pump also on the engine to feed the injectors? Or is the pressure just come from the pump in/after the tank? Oh, and why would the positive lead have a lot of residual current after the battery has been disconnected? Just noticed it with the multimeter when I was testing connections the other day. Tonight I will go through the service manual, surely in the 3000+ pages there should be something.

 

The only pump is the one ahead and above the differential, the filter is also the regulator. You want 58psi +/- maybe 3 psi at the fuel rail.

I don't understand your question about the "residual current", but I THINK I know what you refer to. The document below might help.

Page 10 probably addresses what you are talking about:

 

Hi, just a quick update. So I replaced the Crank Sensor, no change. Also installed the one from my ml500 (same part) but no change. I changed the Cam Sensor with the one from my mercedes (same part) and no change. Going to test the crossfire crank sensor and cam sensors in the merc on sunday. I checked for volts with ignition on at the cam sensor wiring, and seemed ok. The cam sensor wiring plug is toast though - the clip was brittle and broke and the outer casing broke too when i was depressing the tab. Didn't trace it back to the box yet or remove the RCM, but will. Crank Sensor plug was fine though, easy to unclip and nothing brittle. Checked the 200 and 50 Amp inline fuses in the box next to the battery, and those tested fine. I don't think fuel pressure is the issue, strong smell on fuel when trying to start a few times. Didn't get a chance to remove a plug to check for spark, but will Tuesday but I am pretty confident the answer will be no spark. I did noticed after the failed start cycle, a few seconds later, an opening and closing noise emitted from or around the MAF. Going to buy a good merc scan tool, would that be the better way to go before pulling the rcm out? I thought the RCM was more for Fuel than ignition??? Oh and tested the 2 control fuses in the box where the RCM is. Those weren't blown. Being a merc motor of the same era as my ml500 just minus 2 cylinders, I would think it would come up with a start error on the dash. I have seen this before intimidatingly on the ml500 but seem to have sorted that. Crossfire doesn't show anything actually wrong. Tighed1, what does the Fuel Relay do?

 

pizzaguy, I was meaning, after disconnecting the positive battery terminal, there was 12V still in the lead that had been disconnected off the battery and not just for a split second. I mean like 10 seconds after the lead was removed from the terminal. I have been reading the service manual, so from this diagram, power goes from fuse 11 to the coils, and the pcm activates each coil as required? Could that mean that the charge is sitting in the coils and the pcm isn't working correctly, or isn't powered, or could it bad a bad earth? Is there a fuse (or 4) for the pcm?

 

tighed1 is this what you are referring to? That the fuel relay may be staying open and no power to the pcm? Because it does sound like the fuel pump is continually running when I have the key turned and all lights on dash. Not like it's just priming and stops.

 

I am very surpised that voltage holds on the battery lead after you disconnect it, this is not coming from the coils (an inductive item) but from a capacitive item. There are some capacitive items in the car, but I'm still surprised the voltage stays long enough to even measure it. But anyway, no, this is not an indication in and of itself that the coils or ECU are a problem. The cycling of the Throttle Body on a 'no start' is not abnormal. However, if you simply turn the key on, the throttle body should cycle right away, then be silent for a time, then cycle again. If it is constantly making noises, that is a problem.

I speak from experience here , we had a car in GA once that ran very rough and would not always accelerate. If you get the car sit without the engine running and key on, it would almost constantly make odd noises. Replacement of the Throttle Body fixed that car.

 

The BL/RD wire does not power the ECU (PCM) That wire is pulled to ground by the PCM to pull in the relay in order to send power to the fuel pump.
I still wonder what your fuel pressure really is.

 

Hi Pizzaguy, the noise from the throttle body isn't constant, sort of like an end of start cycle noise. I wasn't concerned. But yes, the lead having charge when disconnected was new to me to. I am going to swap the RCM out with the one from the ML as I know it works and see if that fixes the problem once I put the sensors back in the ml I removed to test the crossfire. Once I work out how to carefully remove the rcm. A new RCM is like $200-3$00 bucks in australia on ebay but will look at what tighed1 said and also resolder the back 6 contacts. Have you seen a walk through for replacing the sensor wiring plug here? I see them on ebay pretty cheap, but they dont seem to have instructions.

 

I dont have a fuel pressure gauge pizzaguy but it will be on the list if I can't get it started. Pizzaguy, you don't think it's like the issue you had with your RCM I saw in a post from 2022 is it where yours wouldn't start and you had to bridge the rcm board? I will take the RCM out and send a picture tomorrow if you can take a look.

 

Hi qldcrossfire

Where do you live? I'm in Brisbane and have plenty of spares. By the sounds of it, I'd be pretty sure that it's just your RCM. Send me a PM and I'll give you my phone number.

 

Just for completeness of this thread.

Geoff brought his RCM to my place and I tried it in my Crossfire. The RCM was OK. The issue ended up being a faulty fuel pump.

 

Newbie here! My 2005 will not start on the first crank. After a few seconds of cranking, I turn off car and re-start, Engine will start immediately. I tried to listen for the fuel pump on the initial start, but heard nothing.
What might be the problem? Where is the fuel pump relay located?-in the RCM control ubit? Thanks for your help, Bilbob

 

Bilbob temporarily close the fuel relay and see if she starts. I can replace the relay if it's bad. Email tighed1@hotmail.com for the details.

 

My Ranger was doing that. The issue was that the fuel pump was dying and needed time to get pressure up to 60psi. I'd turn the key to "ON", wait 3 seconds, turn to start and it would start right up.
If I did NOT do that, it would crank and crank and MAYBE start. Turning to OFF and trying again would usually result in a start. Went on for almost a year. Then one day, under a traffic light, it failed instantly.

DJ's suggestion about the pump relay is a good thing to try. Getting him to fix the RCM is way cheaper than a fuel pump, so try that first, the relays on our RCMs are going bad more and more as the cars age. I replaced my RCM last fall and send my bad one to DJ, so now, I have a spare.