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Base timing and TDC offset not lining up

D

Dullahan

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Hi, I've been bashing my head against the wall on this and getting nowhere. The truck is a 99 Hummer, it's OBD2, new P400, new DS4 IP, the ECM has a Heath tune, and I'm using an AutoEnginuity scan tool.

I used Time Set to get the base timing set to 3.5*. I read somewhere that on OBD2 systems, Time Set doesn't work anymore and always just shows 3.5. But I was able to see changes in the base timing with small adjustments to the IP, so I gotta figure Time Set is working and my base timing is locked in where it needs to be.

The problem is the TDC offset. It's at -1.58 right now, and I haven't been able to clear it with KOKO, and it doesn't change appreciably (got -1.50 once) if I do a TDC Learn through the scanner. I'd like the Offset to be around -0.75, which is the top of the range suggested by AM General - my concern is running too hot if the Offset is beyond that since the Hummer cooling system isn't the best one ever hooked to a 6.5.

Engine temps were 170*+ for all tests, it starts good and sounds great. I can see the timing change and hear the engine response during TDC Learn so I know it's doing something. But why is the Offset so far out of the -0.25 to -0.75 range, and how do I correct it without destroying the base timing which seems much more important?
 
I may have this all backward, which would be cool as I like the "turn it 'til you get what you want" solution. Doing that would set my base timing below 3.5*, and posts like this one made me think a minimum of 3.5* was set in stone: http://www.thetruckstop.us/forum/threads/fyi-tdco-timing-the-ds4-injection-pump.11754/#post-144299

Here's the the part I'm talking about, it's a long post
PCM never commands, and the IP cannot respond to, negative advance, or retard, below actual BASE timing - 'nuther words, it cannot go below actual spec'ed BASE timing value .......unless the IP was mistakenly retarded to some degree less than oem-spec'ed minimum of +3.5*
Click to expand...

That post goes on to say advancing 5*, for a total of 8.5* base timing, will give you a -1.5* Offset. And I have a -1.58* Offset with 3.5* Base. The numbers still don't add up.

Am I wrong in thinking 3.5* is an absolute minimum for base timing? Is TDC Offset more important than Base? Is there something wacky with my setup where the Offset is more in line with an 8.5* Base than my 3.5* Base?
 
Time set is for obd1, don't worry about it for obd2. Time set was put in to set the initial timing for obd1 trucks so the timing was close enough for the obd1 ecm to find the tdc offset. Obd2 doesn't require it. That said, there is nothing wrong with a -1.50 tdc offset. Anything below -2.02 shouldn't code for an obd2.
 
I think I get it. My concern with running the -1.50 offset is that the truck would run hotter, and the Hummer cooling system has some issues. I may well go back to -1.50 after the truck has a few thousand miles under its belt and it shows it can keep its cool, but I want a good baseline to tune from. This project has taken a long time, but the light at the end of that tunnel just got a bit brighter. Thanks guys.
 
Welcome to the forum btw.
Figure I needed to leave this one to the ds4 pros.
On overheating, just say no to 220f and she will live a while. Keep it under 210 and it’ll be 300,000+.

What part of the country you in? How is your cooling stack? New p400, guessing (hoping) you just cleaned it. How old and what type of fan clutch are you running? Also which fan blade?

Stick with the AC Delco stats. Do you have Leroy’s BRF?

My plan for my 95 is to pull my optimizer (with about 70k miles on it right now and 150k on the hmco) freshen everything up, and go through the stack. Not sure yet about new factory radiator, aluminum one, or having mine rebuilt at a local radiator shop known for amazing work. No matter what radiator goes back in, it is getting TLTD coating. That increase btu output by 1/3!!!

I am also working on adapting the hmmwv fan clutch to the spin on style waterpump. The normal hummer fan clutch is only 75ish% lockup. Kennedy’s fanclutch is 85%, but need a different fan too. The hmmwv is 100% and rebuildable. I believe between the extra 15% rpm and the TLTD it will keep it good. I have been searching out variable pitch fans also. But I need to do some testing on factory fans to get base line numbers to compare. With all 3, I can not imagine anymore issues.

Are you on the hummernetwork forum? I don’t recognize the name. Sand is leading the charge over there right now on trying for the hydraulic driven fan to mount the 24” fan right next to the radiator like alphas, only hydraulic instead of gfd.
 
Hiya Will, yeah I'm on the hummernetwork forum, different name there (habit from my computer industry days). I've read lots of your posts there - great info! But I wish I read more of them before the stack went back in, my upgrade order would have been a bit different.

The good news on the overheating front is I'm way up in the rust belt (I think that's the first time I've ever used the terms "good news" and "rust belt" in the same sentence), so I don't have extreme temps to deal with. But you know better than anyone what the airflow over these hoods is like, and I've had temp issues with long grades on the interstate without a trailer, and I don't want highway towing to be an issue.

I took the stack apart when it was out and cleaned everything - it was surprising how much junk was in there, because this truck spent most if its idle time in a garage. I'll attach a pic if I have one handy. The fan clutch and fan are the ones from the original engine - my thought at the time was they had under 30k miles on them so they should be okay. That's one of the things I wish I had read more about while the stack was out. Same for the Bypass Restrictor - would have been trivial with engine out, still easy with stack out, a bit of a pain now but still a necessity. At this point my plan is get it on the road, see how it behaves, and prioritize upgrades from there.

It has the spin-on type clutch/pump, and the pump is new. Has Delco stats. Also has boost and EGT gauges so I can keep a good eye on things. I've been following the Humvee fan threads over on the hml, either one would be a cool upgrade (no pun intended).

I wish there was a decent radiator shop around here. There used to be one within walking distance, and another a short hop away, but they're all gone now. From what I hear, with so many new vehicles going with essentially disposable radiators, rad shops are a dying breed. Count yourself lucky if you have a good one nearby. My rad is low miles and looked decent so I should be okay there, but if there was a decent shop near me I'd have sent it out anyway just for peace of mind. Found a pic, here's what the mostly garaged radiator looked like with the coolers off.

DSCN0205.JPG
 
Point of fact: fan clutches loose ~200 RPM per year. At 5 years they are "junk" and need to be replaced. After all who wants a fan clutch that's turning 1000 RPM slower than new? Many get by because they don't need 100% of the cooling, but, on vehicles with marginal cooling systems from the word "go" - lets just say I have sent fan clutches to the scrap yard still bolted to the ruined engine they caused.
 
Yeah, since you are together already, run it and see is what I would try too.

But the yearly loss WarWagon mentioned - if you notice the fanclutches are always labeld “store face side down”. That’s because the fluid inside that engages the clutch seeps out the front when stored horizontally. More use actually keeps them good longer because centrifugal force keeps the fluid away from the seal at the center.

If you get into trying to improve the cooling, ditch factory clutch for a kennedy diesel spin on clutch. It is currently the best one available, and last one I bought was $175, so not bad. No clue if your fan blade will bolt up to it, hummers swapped around mounting patterns too much. If it doesn’t fit your fan, get the 01-05 duramax fan blade. You might need to trim the blade length as some hummers it fits the shroud and some dont.
AM General played with fans and shrouds trying to find easy fixes.

Imo do the BRF @ same time. Haven’t found a single Hummer user yet say it didn’t help.

And yeah, the rust belt comment got a giggle.
 
Thanks guys, the fan clutch is older than 5 years, so it'll be sooner rather than later that I get in touch with Kennedy Diesel. That Humvee rebuildable is sounding better and better all the time.
 
The only problem is there isn’t anyone yet that makes a way to attach the hmmwv fanclutch to the spin on waterpump. Hmmwvs still run the unbalanced 4 bolt waterpumps, and hence destroy the passenger side head and cylinders first.

So although the p400 has metallurgy and outside of cylinder casting problems all resolved, the 4 bolt waterpump would be a mistake to put on there.

I have only tried 1 simple design so far based off just measurements and bolt sizes into a load simulation and it did not look good. I haven’t had time to work on a couple stronger concepts I have yet using the spin on threads. Also looking at adding 4 studs to waterpump pulley to mount clutch like the other one.

All the hmmwv parts will work on hummers except solving the spin on mount, the solenoid to engage is 24 volt instead of 12volt (easily found from about any hydraulic shop or control systems supplier) and thermal sensor to feed the solenoid (easily found any place like summit racing,jegs,etc).

Then if you want a/c to kick it on, just need to add a trinary switch or tap the feed to compressor clutch & relay it. I also want a switch to engage when I choose like about to climb big hill and I want to start cooling early. Also want to power down completely for deep water fording like hmmwvs. Get the rpms high and in water it destroys fans in a hurry. Air fans dont like to be a propeller for a 10,000 lbs bottom dragging boat- haha.

I have been with a couple guys that destroyed fans crossing a river because they wouldn’t just ease into water and wait 2 minutes for cold water to “shut off” viscous fan clutch. One hummer and one jeep. The jeep with fan next to radiator actually propelled fan into radiator destroying both. We strapped his canoe to my roof and filled it with river water to keep refilling his leaky radiator on the way home. Hummer had plastic fan that just broke and lost couple blades.

No one is marketing it with huge success imo because it is an expensive system compared to a simple fanclutch. Me being broke, I only bought a used one- a company has to sell all new parts obviously costing way more.

John of Unique diesel and has it working on pickups with 4 bolt waterpump and a high end control system. He said he could do the spin on waterpump as well, but hadn’t built one when I last spoke to him about it. If you have the nickles, maybe call him up and see if he has it the spin on version Figured out.
He does has i think 2 trucks running the 4 bolt style. But even with the perfect design of the full lockup fan clutch, knowing what I do on the coolant system, I wouldn’t do it with it on the 4 bolt wether original or high output version on mine.
 
Success! For anyone down the road that has the same questions I had, here's how it went. Started with TDC Offset at -1.58 as a result of using Time Set to set base timing to 3.5*. I wanted the offset at -0.75. Did some quick math, which wasn't precise because I don't know how approximate the "1mm = approximately 2*" is, and figured I'd need to move the pump 12 to 14 thou (0.012" - 0.014").

I scribed a line on the block and IP, then scribed another on a piece of steel and measured it - the scribe mark was, coincidentally, about 14 thou wide. Moved the pump the width of the scribe mark - it was too far. Put it halfway back, and offset is now -0.78. Considering I'd probably have to move the IP a couple of tenths (0.0001") to get -0.75, and my eyesight is nowhere near good enough to see that difference, in my case -0.78 = -0.75 and job done! So the pump moved about 7 thou to get from -1.58 to -0.78.

Now the funny part - once everything was tightened up and rechecked I decided to check Time Set just for laughs. And the base timing was still 3.5*! Just goes to show what everyone mentioned above, Time Set is pretty much useless for OBD2. All it takes is some ridiculously small moves of the IP to get the offset right where you want it. Thanks again guys, it was an easy job once I had the right info.
 
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