I'm in the Arizona desert, so I only have my tool bag that I always travel with. Brace yourself, this will be lengthy. The engine will not start unless at operating temperature. I can get it started when I disable the glow plugs and give it a ever so tiny injection of ether. ( I know, don't even go there.) Once the engine is warmed up. It will start and run perfectly normal the rest of the day. I think because the 5v ref is low, it's not commanding enough high pressure oil when starting?

I believe I have a voltage problem in the cab? I think it's a ground or B+ issue?

The tack needle does not move when starting the engine and the OBD port is dead when starting the engine, so the PIDs can't be scanned while starting. No codes, all lights and other systems are functioning normal. New Motorcraft CPS, IPR, ICP and 2 Decca 850 cca batteries. Some desperation, (I have found that sometimes doing things not logical will work.) The engine was rebuilt 37,000 miles ago, including engine harness and all multi-pin plugs and connectors. All under hood ground points were shored up. PCM was tested and is good per Jon. The Hydra is removed. Disconnecting the ICP, does not help. All fuses, relays and the PCM diode has been tested and is good. Cam gear and crank gear are welded. (Modified HPOPs have been known to walk the cam gear.) I tested the CPS circuitry from CPS plug to the PCM plug and it's fine. I removed the CPS and waved a wrench back and forth in front of it, the misses stated the tach needle moves. Obviously there are no scratches on the CPS face.

I had it at the local Ford dealer for three days. They can not fix it! I was told it's an old truck. REALLY! I was charged $100. I thought about taking it to the dealer in Lake Havasu. Because of it's snow bird season, they do not even give an appointment. They will give you a date to drop it off and they will get to it when they git to it. Just no. Now I might need to reconsider that?

Today, I'm going to take the day off to research this and drink a few IPAs.

Tomorrow, I'm going to find all cab grounds and shore them up. Then I'm going to connect one jumper cable from the frame to a stout point on the cab.Try it, hmm? If no go, I'm going to check the B+ connection to the fuse box under the dash. I should do that anyway. My objective is to have solid 12 volt power in the cab a get the OBD port working while starting. I have noticed the cigarette lighter doesn't work if the OBD port is dead, same circuit. Nice!

What say you? Any thoughts or suggestions? I really hate using ether, but I have no recourse. I double posted this just to get more exposure.

 

Yes the power point and OBD2 are on the same fuse, which one escapes me at the moment but I'd just replace it. To many people have been bit by a fuse that looked and tested good, make sure the contacts are clean and tight then throw in a new one. The only starts with GP disconnected bit is suspicious. I would be checking that wiring very close,. Possible short robbing power?

 

Stupid question have you verified the glow plugs are functioning. This sounds like there not to me. Have u checked for voltage to them and ohmed the glow plugs. Also what yr I think 02 and 03 the tach isn't supposed to move while cranking.

 

Why do you suspect low vref? Have you checked it is it the same on all circuits or is it one individual circuit that is low?

 

Thanks for the quick reply.

I disconnected the glow plugs because their not needed when using ether and reduces/eliminates kicking. Because of the seriousness of this issue. I used my multi-meter to test everything. Double and triple checking too. I'm taking no chances.

I screwed a 1/8" drain **** into the intake wye. That makes it easy and I can use a much tinier amount of ether right before it enters the intake manifold versus by the air filters and travel through the intercooler to get to the engine.

If I was home, not in the desert. I would use my power supply to power the OBD port for diagnostics.

 

Static vref is fine. I'm not sure it is when starting and B+ is pulled down? It's one unknown that needs to be validated.

I haven't been able to check the 5v ref at the sensors while the engine is being cranked because I'm alone here in the desert. The misses is visiting family in Wisconsin. My "travel" multi-meter doesn't have record. I don't have my current clamp either. I would like to check the starter amps during cranking also.

What is the absolute minimum voltage a 7.3 will start with? I googled it and of course get conflicting answers.

 

Glow plugs are indeed working and it's a 1997.

Does anyone actually look at signatures? That would be helpful.

 

They don’t show up on mobile devices. You can get to them but it requires some dance steps.

 

Sig's don't show on mobile version of website.

If the GP's are only being disconnected to prevent preignition of the ether then that takes them out of the diagnostics. We're looking more at a short in the ignition system then. It's where I'd start at least.

 

I didn't know that about the sigs, thanks.

 

Yeah - sorry about that - it's frustrating for many of us as well. I have several links in my signature that point to helpful troubleshooting threads and info, but folks on mobile devices cannot see them, so I have to post the links over and over in each new thread, wasting time. No dark mode for FTE either.

But...still the best place to find help and contribute for these rigs - due to the people here!

 

I know on the early 99 it was undet 10.5 volts the idm wouldn't fire the injectors. I would imagine it to be the same but I can't say with certainty. I also believe the pcm requires 150 rpms to fire them.

 

10.5 volts sounds reasonable to me. Some were stating 9.5 on the web which I'm skeptical of. I do believe the problem is low volts (brown out) while starting? There is a reason why the tach needle moved when I waved a wrench in front of the CPS with no engine cranking and nothing while it is cranking.

I did some tracing on my wire schematics and verified the tach does get it's signal from the PCM. I assumed that, but wanted validation. I'm thinking low voltage is causing the OBD port to go dead and the PCM is off line, which is causing no tach needle and no codes? Is the wait to start light supposed to be on during starting?

 

A lot going on here...

Ford states a minimum of 10.2v while cranking to start the engine. We usually say 10.5v because it provides a bit if a cushion and is easier to remember.

The wait to start light comes on for a few seconds when switching the ignition from OFF to ON.

If the wait to start light dies not come on, the PCM is not receiving the required 12v power and the engine will not start.

The CPS is a hall effect sensor.

All of the above applies to a 1999 - 2003 7.3L PSD, but may also apply to your 1997.

 

Have you checked voltage at the OBD port while cranking? Does it go to nothing, or just not enough for the scan tool? Knowing specific voltages when cranking would be valuable. That could explain why ether works. That kicks the motor off and you stop cranking, letting the voltage rise. Have you tried starting it with jumper cables or a jump box connected to your pickup? And just to verify your condition...is this only happening when cold, and normal starting and operation with no chemical assistance when warm?