Engine/Transmission (1998.5 - 2002) 99 When at operating temp, engine hard to start

[Diesel David]

Code P1693 --- PCM ? Would like to know what the most complaints are for --with this code.

 

[KATOOM]

The p1639 code is a "companion code". When this code pops up, there is supposedly another code inside the PCM which requires a decent scanning tool to retrieve. If no code is found then it could merely be generated by a glitch in the system from electrical interferences of electrical components working out of parameters, like a dead battery cell or an alternator issue. Other than that, lets address how and when your truck hard starts.

Does this ONLY happen when its hot and when you momentarily shut off like at the gas station or store, only to come back to a truck which doesnt want to start very easily? Or.....does it hard start at ANY OTHER TIME. Thats important to know.

 

[Gary - K7GLD]

You have to wait for the complete error codes cycle, after doing PCM and ECM check, with any resulting codes, the readout will return to registering miles - until it does that, the check isn't complete. The 1693 by itself is sorta meaningless - it's the following codes that tell what's wrong.

 

[Nigel]

Next time it doesn't want to start. Open the hood and disconnect the temp sensor by the thermostat and try to start. If it starts right away the problem is probably in the VP pump. I had this happen on 3 24 valves and the only cure has been to change the pump. I think it is in the electronics. By the way it will throw a code when you try this but it will go away after a couple of starts after you plug the sensor back in.

Nigel
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[KATOOM]

Next time it doesn't want to start. Open the hood and disconnect the temp sensor by the thermostat and try to start. If it starts right away the problem is probably in the VP pump. I had this happen on 3 24 valves and the only cure has been to change the pump. I think it is in the electronics. By the way it will throw a code when you try this but it will go away after a couple of starts after you plug the sensor back in.

Nigel
.

In all the years I've been part of many Cummins forums, I've never heard that unplugging the thermostat temperature sensor did that. Where did you hear this? Not saying its wrong but just really odd that this would do anything since there is no reason the VP would have PSG issues which relates to the thermostat.

Now unplugging the "fuel pump fuse" is a common trick for determining excessive fuel pump pressure during engine cranking.

 

[Nigel]

When it first started happening to us we observed that it always started perfectly when cold. So when it wouldn't start warm we thought is there a way to trick the truck to think it was cold. So I unplugged the temp sensor to try, not idea if it would work but knew it couldn't hurt. What do you know the engine lit up instantly. So then we tried the same thing on my friends truck he was having the same problem and his started instantly. I don't know enough about the pumps to explain why it works. This was back around 2000 both our trucks were 99's out of warranty and the dealers were not much help in diagnosing the problem at the time. My current ruck did the same thing about four years later.

Nigel

 

[NIsaacs]

The best thing you can do for a VP truck is run on the top half of your fuel tank and on a hot start, hit the start position instantly, don't let the lift pump run.

Nick

 

[Gary - K7GLD]

Not sure on trucks other my '02, but there is an overheat engine protection Limp Home function of the ECM that will shut down half the engine - in other words, only fire on 3 cylinders in an alternating firing order as a Limp Home feature - never actually heard on anyone experiencing that, but seems if the ECM was seeing what it thought was excessive coolant temperature, and was in that limp home mode, might be hard to start - and unplugging the temp sensor could fool the ECM into thinking temp was OK...