Intermittent starting and a clicking - 7.3
Thread Starter
Joined: Aug 2006
Posts: 3
Intermittent starting and a clicking - 7.3
I have a 2000 F550 that does not start reliabily. Sometimes, when the ignition is turned on, you hear clicking from multiple relays - behind the dash as well as the IDM relay. The IDM relay is controlled by the PCM and the signal from the PCM is going up and down causing the IDM relay to chatter.
If, when the ignition is turned on, the relays do not chatter, it usually starts.
If the IDM relay is run mannually it starts fine.
The CPS tests fine - reads RPM etc.
The PCM was changed.
Currently the Manifold heater is bad and waiting for the part - but we simulated it and it did not affect the problem.
No codes are being stored.
The fuse links were changed.
The grounds have been checked and rechecked.
The various connectors have been checked and are clean and pins seems to be fine.
Help - anybody seen anything like this?
If, when the ignition is turned on, the relays do not chatter, it usually starts.
If the IDM relay is run mannually it starts fine.
The CPS tests fine - reads RPM etc.
The PCM was changed.
Currently the Manifold heater is bad and waiting for the part - but we simulated it and it did not affect the problem.
No codes are being stored.
The fuse links were changed.
The grounds have been checked and rechecked.
The various connectors have been checked and are clean and pins seems to be fine.
Help - anybody seen anything like this?
Super Moderator
Joined: Jul 2006
Posts: 7,555
RE: Intermittent starting and a clicking - 7.3
Is the PCM relay clicking/cycling along with the IDM relay? Key on power distribution for both comes through the PCM diode in the battery junction box, drawing off of the CJB PCM fuse.. Any other power distribution issues that accompany the relay functionality?
Thread Starter
Joined: Aug 2006
Posts: 3
RE: Intermittent starting and a clicking - 7.3
In answer to your question about the PCM relay - no it is not clicking, just the fuel pump and the IDM relays.
We tried replacement diodes as well.
The IDM relay gets power from the same point that the PCM relay gets power, but the ground side of the IDM relay is normally pulled low (to energize) by the PCM module.
- We measure the ground side pulsing, seemingly because of the PCM.
- we measured the voltage into the PCM and it is steady.
It feels like one of those cyclic things - a load pulls the voltage down and something drops out, when it drops out the voltage goes up again and then things look normal so the load goes on again - which causes something to drop out. Cranking is continous and seemingly normal - it just decides not to start when ever the chattering occurs.
How sensitive are these things to battery voltage? If one battery gets poor what happens?
We found two identical descriptions of like problems when we searched the forum, but there were no responses as to the fixes. We emailed the people to find out what they found - so far no luck.
Does the oxygen really help?? (on the bike)
We tried replacement diodes as well.
The IDM relay gets power from the same point that the PCM relay gets power, but the ground side of the IDM relay is normally pulled low (to energize) by the PCM module.
- We measure the ground side pulsing, seemingly because of the PCM.
- we measured the voltage into the PCM and it is steady.
It feels like one of those cyclic things - a load pulls the voltage down and something drops out, when it drops out the voltage goes up again and then things look normal so the load goes on again - which causes something to drop out. Cranking is continous and seemingly normal - it just decides not to start when ever the chattering occurs.
How sensitive are these things to battery voltage? If one battery gets poor what happens?
We found two identical descriptions of like problems when we searched the forum, but there were no responses as to the fixes. We emailed the people to find out what they found - so far no luck.
Does the oxygen really help?? (on the bike)
Thread Starter
Joined: Aug 2006
Posts: 3
RE: Intermittent starting and a clicking - 7.3 - FIXED
Fixed but I am a bit embarrassed.
The problem was the batteries and I was fooled... Next time I will check them by separating the two batteries and trying to see what the cranking voltage is on each one.
It cranked over well but during the inital battery drain as the key was turned on (to get the plugs heating) there was a problem. Apparently the voltage went too low and something stopped it from starting. There were other problems, but this was the root of the problem. Something is sensitive to voltage and it was not the PCM.
Live and learn...
Super Moderator
Joined: Jul 2006
Posts: 7,555
RE: Intermittent starting and a clicking - 7.3 - FIXED
Glad it fixed..
The PCM needs to see a 'minimum' of 100 RPM (text book is 150-200) or the IDM won't fire the injectors.. I think the 'minimum' battery voltage for PCM power up, the relays, VPWR during cranking is 8.0.. Or you'll probably get your rattle!.. Although a spec speed/IPC won't be met for start.. Odd that the fuel/IDM relays clicked/rattled, but the PCM relay was powered/energized and stayed closed.. The fuel pump relay gets it coil power from a closed PCM relay, and the 2 relays (IDM/Fuel pressure) share a common control from PCM ground manipulation as you mensioned.. PCM relay must have seen intermittent voltage which would explain the grounding/power up issue to the other relays..
This has happened to alot of folks with aged batteries when their cranking, the speed/sound seems good, but any good draw like glows, A/C, lights, kills or dips the speed below spec..
I just had one in the other day that had a 'brand new' set of batteries, and over a few days would completely drain the power.. Sometimes less.. I thought for sure it had to be a parasitic draw, (why the new batts) and started doing some looking.. found nothing, but they died out a few times while testing, and of course a few no starts for low battery voltage.. This truck also had added on 2 way radios/lights ect. But during/after a charge, found the left battery hot.. Even uncabled, a dieing/shorted brand new battery, .. Sometimes you just get thrown a curve
The PCM needs to see a 'minimum' of 100 RPM (text book is 150-200) or the IDM won't fire the injectors.. I think the 'minimum' battery voltage for PCM power up, the relays, VPWR during cranking is 8.0.. Or you'll probably get your rattle!.. Although a spec speed/IPC won't be met for start.. Odd that the fuel/IDM relays clicked/rattled, but the PCM relay was powered/energized and stayed closed.. The fuel pump relay gets it coil power from a closed PCM relay, and the 2 relays (IDM/Fuel pressure) share a common control from PCM ground manipulation as you mensioned.. PCM relay must have seen intermittent voltage which would explain the grounding/power up issue to the other relays..
This has happened to alot of folks with aged batteries when their cranking, the speed/sound seems good, but any good draw like glows, A/C, lights, kills or dips the speed below spec..
I just had one in the other day that had a 'brand new' set of batteries, and over a few days would completely drain the power.. Sometimes less.. I thought for sure it had to be a parasitic draw, (why the new batts) and started doing some looking.. found nothing, but they died out a few times while testing, and of course a few no starts for low battery voltage.. This truck also had added on 2 way radios/lights ect. But during/after a charge, found the left battery hot.. Even uncabled, a dieing/shorted brand new battery, .. Sometimes you just get thrown a curve
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