Rough idle diagnosis

[Glassdude]

Here are the symptoms. Idles rough when cold, gets worse as motor warms up. Stumlbes and misses on acceleration. I have changed the UVC harness and valve cover gaskets. Ran a CCT with AE and got code P0284 Clylinder 8 Fault/Balance. Injector buzz test was normal. Looked at PERDELS for each cyl. Cyl 3 varied between 1.2 and 2.3. Cyl 8 was between 5.9 and 7.6. Checked the Inj Control Pressure - varied between 475 - 490 at idle. Inj Control Pres volts - .78 - .90. Inj Control Duty Cycle - 9.7% - 10.16%.

I'm thinking I need a new injector. The truck has 240,000 on the clock. What else can I check other than fuel pressure which I'll get this weekend?

 

[BIG JOE]

With only 475-490 psi HPOP pressure.. sounds more like a HPOP issue (?).

A 7.3 needs a [Minimum] of 500 psi, as you crank it, and at idle.. to "POP" the injectors properly.

Low HPOP pressure could be the leading issue to all the other scan results ?

Joe

 

[Glassdude]

Could that be a problem with the IPR or HPOP? I did check the oil level and it was about 1/2" from the top. I have heard that the pressure should be 500 or above to start but there would be a drop as engine warms up. EOT was 130 when I checked the data.

 

[BIG JOE]

Those low HPOP pressures could/would be influencing what the IPR senses. The oil level in the HPOP can be where it needs to be, but it's a gear pump, if the tolerances are going= low pressure.

I'm away from home (RV'n) but IIRC.. 500 HPOP psi minimum.. is what is required to pop the injectors correctly.. cold or op temp. 150* is also the minimum temp for alot of ECM/PCM functions to come into play.. for scanning perposes ?

Anyone else ????

Joe

 

[Glassdude]

Had a new devolpment today. I was going to hook up a fuel pressure gauge and change the fuel filter. Filter only has about 3000 mi on it but you never know. After the filter change I started it up. Ran pretty good for a minute and then just died. Now it wont start. I opened the fuel bowl to see if something was wrong and the filter was dry as a bone. The fuel pump quit. I'm hoping this might be the problem. I guess a new pump and time will tell.

 

[BIG JOE]

Yep.. It's a proccess of elimination. Check yer fuses first, and under the hood relays ? The lugs on the relays & Maxi fuses can get corroded.. over time.

Joe

 

[Glassdude]

Thanks Joe I did check the MAxifuse under the hood but I can't find the relay. Anybody know where it's located in an 01?

 

[BIG JOE]

Check the fuse for the Fuel heating element.. If bad, R& R it. Then, disconnect the fuel heater @ the fuel filter bowl. Turn the key on and see if you can hear the fuel pump running. If you can't hear it.. with a test light.. see if you have 12v AT the fuel pump.

Doing this will tell you.. The fuel heating element has shorted out.. or the fuel pump has, in fact.. gone south ?

 

[Glassdude]

Replace the fuel pump. New pump has good flow judging by the amount of fuel on the ground as I realized I left the fuel bowl drain open. Now it will not start. Checking with AE I had the following readings during cranking. Power - 11.1v RPM - 135 ICP - 1.3v Fuel Pulse 3.6. I had these readings until the batteries started to tire. What else to check after recharging the batteries?

 

[Glassdude]

Finally back on the road again. Turned out the seal on the brass poppet in the FPR was torn up. Couldn't get more than 30psi. Got the rebuild kit from Diesel Orings and all is well with 60psi. Idles real smooth and runs better than it has in awhile.