new member - 89 7.3 IDI timing issues

mclarkva

Registered User
Joined
Jul 20, 2018
Posts
7
Reaction score
0
Location
Charlottesville va
I am a little confused on the the timing and the advance cam on the DB2 injection Pump.

Working on a 1989 F350 that seems to have timing issues, maybe some drippy injectors, and a bit of low compression miss on cylinder 3. (Aside: I have had 2 engines fail at cyl 3 one cracked cylinder wall- a Reviva reman and another lost rod bearing -what's up with cyl 3?)

Anyway the timing seems weird - using Rutunda with luminosity (have the pulse module but the Rotunda tool is 1982 and doesnt seem to work with the pulse mudule) If i set the luminosity into cyl 1 and set the timing offset to -20.0 and then set the timing at 2000rpm to 8.5 when dropping back to high Idle (its a refer truck and idle is set to 900RPM) I see 14 deg on the Rotunda ?!

Is this right? - well the truck can barely get moving out of a parking spot set like that and very smokey. So i retard the timing significantly from this carefully adjusted point and with idle at 900rpm at no more than 10 deg the truck will move nicely but by 2000rpm the timing is less than 4 deg still smokey. To clear most of the smoke (other than the #3 miss problems) and have the truck still move but not very powerful the timing ends up near 0 at 2000rpm and about 4.5 at 900rpm idle and of course its a bit harder to start.

I dont understand this IP timing behavior - is the IP advance cam gone wrong? it does seem to move the plunger ok from the outside view.

I have a rebuilt IP in a box and a reman set of 8 injectors and a pop tester at the ready, ive also arranged for a reman engine so i can pull this one to work on Cyl 3 but the refer truck is in use almost daily and we dont want to take this delivery truck out of service so I would like to get this running better until we can swap the engine - I am just obsessed with understanding why it is doing this and what I am not understanding - school me please!
 

bbjordan

Snow Monkey
Joined
Feb 24, 2011
Posts
1,421
Reaction score
393
Location
Ashern Manitoba
That actually make sense. Using the luminosity probe, the timing spec is 2* ATDC +/- 1 *

One other thing to note, the "Advance" cam is actually a retard cam.


Edit: Welcome to Oilburners!
 
Last edited:

mclarkva

Registered User
Joined
Jul 20, 2018
Posts
7
Reaction score
0
Location
Charlottesville va
Ok so I'm the idiot using pulse numbers with a luminosity probe!

So the retard cam and the internal pump piston itself both retard as rpm increases?

At what point should I set the face cam by rotation on its shaft? ...should I set idle timing 1.0 BTDC and then go back to 2000 rpm and adjust the face cam to achieve 3.5 ATDC?
 
Last edited:

mclarkva

Registered User
Joined
Jul 20, 2018
Posts
7
Reaction score
0
Location
Charlottesville va
I've seen these from Snap on MT480 luminosity


1.0˚ BTDC @ 700 rpm
2.0˚ ATDC @ 1400 rpm
3.5˚ ATDC @ 2000 rpm

I was way advanced using the 78-0100 rotunda with 8.5 BTDC at 2000 ... No wonder it was smokey and could not move...started easy though!
 
Last edited:

bbjordan

Snow Monkey
Joined
Feb 24, 2011
Posts
1,421
Reaction score
393
Location
Ashern Manitoba
So the retard cam and the internal pump piston itself both retard as rpm increases?

The cam retards the timing as the fuel demand is increased. The internal piston advances the timing as the fuel pressure in the IP case increases with higher rpm.

The "Light load advance cam" is set when the IP is calibrated on the bench, and generally should not be touched, unless you know what you are doing. That being said, I believe @Macrobb has experimented with the cam and probably has some insights.
 

Thewespaul

Supporting Member
Supporting Member
Joined
Jul 27, 2015
Posts
8,796
Reaction score
8,058
Location
Bulverde, Texas
I’m working on some adjustments, it’s actually referenced as the “face plate” in pump shop lingo, but advance cam is what it’s referred to here mostly. I like to set it so at idle it’s just below the start of the ramp on the cam, this makes for a bit snappier throttle response and can help get a worn pump closer to original performance. You can completely remove this part and the advance arm and the truck will run fine, but will have very little timing change throughout the fuel curve. I am using this on the shop truck to make my own timing curve
 

mclarkva

Registered User
Joined
Jul 20, 2018
Posts
7
Reaction score
0
Location
Charlottesville va
Thanks!

Yes I operated with the shaft clamp screw loose but didn't fiddle at all with the painted set screw at the plunger ... effectively removing it from the system. This is where I saw my IP continue to retard at higher rpm and began to think the IP was bad.

I gave it a little Gap till maybe 1100 to 1200 rpm before the face ramp started to take effect as you mentioned. And that does seem to get a bit more snappy throttle response. This truck is heavy around 16000 with the refer box and engine driven Thermo King compressor in addition to my AC ...it's not a hot rod!

I am intending to swap out this motor but have to get the truck to another Saturday Farmers market tomorrow at 5am.

I settled on ( however accurate or repeatable this Rotunda Lumi meter is) on about 6.5 BTDC at idle and near 0 at about 2000 rpm continuing to retard to maybe 2 ATDC at 3000... I wasn't going to hold the throttle and stick my head under the hood for that. I never saw the pump advance at all even with the face cam out of service. Only advance was electric cold start.

You think this IP is worn out...since I never see advance at higher rpms?

I've not yet tested the injectors but in the past and on other 7.3idi that I have checked at this age the old injectors open way before 1900 psi maybe even begin weeping at 900 to 1000 psi
 
Last edited:

mclarkva

Registered User
Joined
Jul 20, 2018
Posts
7
Reaction score
0
Location
Charlottesville va
It running nice enough now I'm questioning my decision to pull the motor ...
Still smokes at times a little blue so another compression test ...and injectors are still suspect as a few random knocks come and go like intermittent leaky injectors...
 

Latest posts

Forum statistics

Threads
91,217
Posts
1,128,473
Members
24,044
Latest member
Mnlx

Members online

Top