Cat 3126 B won't start ****HELP***

The sensors are under the high pressure pump assembly, mounted in to the front cover. Do not bent the bracket. You need to remove the bolt that holds the bracket and you will be prying up on the bracket to un-clip it from the bottom sensor leaving the bracket on the upper sensor. You can fish out the lower sensor, unplug it, change it with the new one and reinstall with the upper sensor still in place. Now remove the upper sensor with the bracket installed, it with fish out, abit tight but will come out. Unplug and install new upper sensor with the new bracket. Install the upper sensor, now with two pry bars you hold the bracket against the lower sensor and push in on the bracket, this will clip the bracket back on the lower sensor. Try to clock the lower the sensor so the bracket will hit the right spot. Take a look at the new sensor, you will see what I mean. The bracket has to clip on to the sensor in the right spot.

 

Its going to be hard to change that sensor in a RV, even if you have done them before in a regular cab config. Yes, a weak number two engine speed sensor will cause an intermittant no start. I have had engines with no codes have a failing sensor with a no start. The engine can not find top dead center and will not fire the injectors until it see,s it. The sensor is weak so when you fire it with starting fluid, you speed up the rpm and the sensor picks up a signal.

 

You will not be able to loose the air compressor that easly. There is a support bracket at the rear of the commpressor, you will need to pull the power steering pump to get at the bolts. That bracket must be torqued back up properly, or the front cover can crack.

 

if your still having the problem check this, injection actuation sensor on your 3126 it will be on the left side of the engine towards the front top next to the valve cover. Unplug this sensor if it starts then thats your problem, replace it and your good to go. It is extremely common, just happened to my 2000 F750 mechanics truck today, happens to CAT excavators quite a bit. alot easier then reaching behind the air compressor for the primary and secondary speed sensors.

 

I have a 1998 FL70 with a 3126 and I'm fixing to replace both sensors tomorrow when they get here. Are there any tricks or things I should know about before hand?

That space looks pretty tight in there.

Thanks for any advice.....

 

I have a 2003 GMCT7500 Pole Digger with a Cat 3126 which has thw same cold starting problem. I have replaced the fuel pump, IAP sensor, fuel pressure regulator and both speed.timing sensors. However it still only starts with starting aids if it is left for more than 3 hours. Any ideas?

 

Tallboy......I'm going through this myself. I've replaced both speed/timing sensors, fuel pump solenoid, new fuel lines, fuel check valve on back of head. I just got some injector o rings and will try that before I replace anything else.

I've read where a cracked injector o ring can create a no start (leaking fuel).