Cummins 6CTA8.3 Injection Timing

[74M35A2]

So upon reading other forums where the Cummins 8.3L is used extensively (RV motorhomes), it appears that most of them recommend the injection pump timing be advanced to about 16 degrees to greatly improve mileage, and other mods will take a much better hold.

It seems as if our MW injection pumps have oblong mounting holes, which would tend to allow some adjustment in injection timing. The pump itself appears to be very similar in layout to the more common Bosch P7100, but with a different governor.

So question becomes, has anybody advanced the injection timing on their M939 series 8.3L? If so, how did you do it, and what were the results? Did you do it by measure (#1 injection plunger height as measured via dial indicator after removing delivery valve)? I'm looking to do it via this method, but don't want to spend $500 in Miller tools to do it once. I do see P7100 injection timing tool kits on eBay for about $175 range, and can probably get the injection timing table for an 8.3 from any local Cummins dealer. I have not studied it close enough yet, but it appears there is a front access port cover to pull and re-index the injection pump gear (as done on the P7100 equipped 5.9L's in Dodge Ram trucks), if necessary.

Thanks in advance.

 

[sweetk30]

x2 ..

I got a replacement engine in the 936a2 and its running 14 or so timming . original was 8.0 tmming .

seems to be low on power / throttle response . wana know if playing with timming back to mill spec engine will work better.

 

[74M35A2]

How do you know your replacement engine is at 14 degrees? Did you measure this, the engine data plate says so, or somebody just says that is what it is at for the engine you acquired?

 

[sweetk30]

data plate .

 

[nevrenufhp]

On some data plates they state timing at the pump, not the crank. So, your 8 degrees may actually be 16.

 

[4XDesign]

So upon reading other forums where the Cummins 8.3L is used extensively (RV motorhomes), it appears that most of them recommend the injection pump timing be advanced to about 16 degrees to greatly improve mileage, and other mods will take a much better hold.

It seems as if our MW injection pumps have oblong mounting holes, which would tend to allow some adjustment in injection timing. The pump itself appears to be very similar in layout to the more common Bosch P7100, but with a different governor.

So question becomes, has anybody advanced the injection timing on their M939 series 8.3L? If so, how did you do it, and what were the results? Did you do it by measure (#1 injection plunger height as measured via dial indicator after removing delivery valve)? I'm looking to do it via this method, but don't want to spend $500 in Miller tools to do it once. I do see P7100 injection timing tool kits on eBay for about $175 range, and can probably get the injection timing table for an 8.3 from any local Cummins dealer. I have not studied it close enough yet, but it appears there is a front access port cover to pull and re-index the injection pump gear (as done on the P7100 equipped 5.9L's in Dodge Ram trucks), if necessary.

Thanks in advance.

I have also been trying to research advancing the timing. The holes are oblong on the pump but the studs are at opposite ends of the holes so to me it looks like the pump cannot be rotated. Have you made any progress advancing the gear? I have been searching for ways to continue to lower EGT's. I have done the following, air intake modification, gutted very restrictive after cooler and big air to air added. Let us know if you have made any head way.
Thanks

 

[74M35A2]

I have also been trying to research advancing the timing. The holes are oblong on the pump but the studs are at opposite ends of the holes so to me it looks like the pump cannot be rotated. Have you made any progress advancing the gear? I have been searching for ways to continue to lower EGT's. I have done the following, air intake modification, gutted very restrictive after cooler and big air to air added. Let us know if you have made any head way.
Thanks

Your charge air cooler looks great. Let us know which one it was, looks like it fits like a glove. Also, how did you attach it? Looks like it bolts to the radiator tanks, but I must be seeing it wrong. Any hood closure issues or does it fit?

On the timing, I have a Cummins dealer that says their service dept can do it. I am still torn between buying the tools myself and doing it. My next step here is to pull the tach drive flange and see if that is enough room to pull the pump gear off. I thought I have seen the MW injector pumps listed on eBay, and it had a keyed gear shaft....? In that case it must be done differently somehow. I will visit the Cummins dealership to try and get info on this, including the timing table, I'll report back with the info. If you can use the 5.9L dial indicator, which I think you can, then I may just do it myself. I will search more eBay MW pumps and check the pump shaft also. If keyed, then no use in going that way, unless you bump it by re-indexing tooth alignment.

The intake air mushroom is supposed to be restrictive also, diameter is same as M35A2, but the intake tube is larger, leaving a smaller surface area screen for inlet air.

 

[4XDesign]

Mounts for cooler

 

[74M35A2]

Got it, thanks.

 

[nevrenufhp]

By chance, has anyone called in to a Cummins dealer with their ESN to see what the factory timing is supposed to be?

 

[74M35A2]

By chance, has anyone called in to a Cummins dealer with their ESN to see what the factory timing is supposed to be?

The data plate on mine says 8 degrees. That is the same data plate that has the ESN, so I wouldn't expect a different answer unless I am missing something.

The Cummins dealership by me said they would advance the timing to the maximum amount allowed per my engine CPL. Upon calling them again and begging, they said they would advance it to whatever I specify, and charge me an hourly rate to do so. So now the question becomes is it cheaper to buy the tools, or cheaper to pay them. My target after a few hours of searching seems to be 16 degrees.

 

[fattboy123456]

Please keep us updated im very interested in this

 

[74M35A2]

I will. Was going to take it in this week, but aunt died (was not close with her). So, moved to next week Mon. I am going to tell them to assess the situation first, as if they predict more than 4 hours of shop time to do so, then I will just buy the tools myself and go that route. From what I see on eBay images for our MW injection pumps, the shaft and gear looked keyed together. The IP looks like it can be clocked some (?), so if clocking the pump alone does not reach 16 degrees, then I would think the pump and gear would have to be pulled and shifted a tooth then try again. The P7100 pump does not have a keyed shaft and gear, and therefore they just re-index the gear on the IP shaft to change timing.

Basically, if they say they will have to pull the timing cover apart, I will tell them to forget it, and I will do it myself. Usually the pump gear access hole (where the tach drive adapter is) is large enough to do this adjustment. We'll see, uncharted territory here..... Advancing timing is supposed to greatly increase fuel economy and decrease EGT's. 16 degrees seems to be the safe limit on this engine from reading posts on the RV boards where those guys are always pressing for more mileage and power simultaneously. Anything over 16 degrees over-stresses the head gasket area/head bolts/etc.... Not much power increase in do this itself, but other mods take much better hold when doing so. Again, this is just my collection of other opinions from random places. Factory timing on my M925A2 states 8 degrees on the Cummins ID tag.

 

[fattboy123456]

Im really surprised that for how common this motor and MW pump is that there is no Pictures or video detailed how to do it
I mean between RVs, military trucks, heavy equipment, and Ford trucks No one has a wright up or video.....and I have looked as well for it too

 

[nevrenufhp]

Im really surprised that for how common this motor and MW pump is that there is no Pictures or video detailed how to do it
I mean between RVs, military trucks, heavy equipment, and Ford trucks No one has a wright up or video.....and I have looked as well for it too

I should have some time starting in December, if you want, you and me can get pix and video of yours getting timed.

 

[74M35A2]

Im really surprised that for how common this motor and MW pump is that there is no Pictures or video detailed how to do it
I mean between RVs, military trucks, heavy equipment, and Ford trucks No one has a wright up or video.....and I have looked as well for it too

Not a lot of them have Bosch MW pumps. Seems to be prevalent in 939A2 series and some agricultural applications. The Bosch P7100 pump is more common I believe (much higher volume school buses and motorhomes). The MW has a very similar looking in-line pump, but governor is completely different, for whatever reason.

Stay tuned (get it?), hope to drop the truck off Monday at lunch and have some feedback or task complete by mid week. I don't have an EGT installed yet, but I will try to at least get one temp mounted to know the effect of this beyond the seat of the pants dyno.

 

[HETvet]

I just so happen to have access to cummins quick serve. Give me ESN and I'll beable to get you what ever info you want. I also have unlimited access to ISIS (international) and what ever Detroits factory info website thing is called. I also ha e connections in to cummins southern plains off of I20 in Dallas texas

 

[74M35A2]

I also have free access to Cummins QuickServe (everybody does), and I can't seem to find any useful injection timing info. They talk about IP spill port timing, and they show the dial indicator to measure plunger #1 height ion their tool section of that chapter, but there is no table or chart or how-to for this method. I was expecting to find a timing table of plunger height vs crank degrees. I have not read it in depth though, and have yet to do that. This is easy to find on the internet for a 5.9L with the 7100 pump. My ESN (Engine Serial Number) is: 44455234 (saved within and working with Cummins Quickserve), please try to find timing info beyond what I did if you can.

I bought a full size Volvo road tractor intercooler, same as member 4xdesign did. He did a fabulous job of measuring to find the best fit one, and then installation also. I am copying that. But, I want to install my EGT before I do any mods, so I can accurately report their effect. Advancing timing is supposed to reduce EGT, as well as dumping the muffler.

 

[74M35A2]

OK, so after more study of the service manual on the Cummins Quickserve portal, it looks like the 8.3 injection timing is set by monitoring flow out of the #1 injection line, while supplying 300-375psi of fuel into the injection pump. Rotate the engine until the flow slows to a drip, and read the crank timing tape. That is the basic procedure, much abbreviated.

 

[HETvet]

I've got a little bit more than free access. Glad you were able to get the information you were looking for though