Fuel Mileage VS Timing

[Kalashnikov]

Well, I put new injectors, turbo IP, and electic lift pump in my 89 N/A back in August. I was running 40s for a while with stock 3.55s and I was getting what I thought was about 9-9.5 MPG doing probably 60/40 highway/city. I run a 50 gallon tank in the bed and I had only run it completely full to empty once. I did the 40s not long after the new stuff so I never got a mileage reading before. I was getting 17mpg on the old a pump last year.

I this last tank I got 426 miles running 33s. It reads about 2.3% low on mileage but still, that's under 9 mpg! I think I might be forgetting something I calculated wrong last time because I only got 375 miles from full to empty with the 40s. EDIT: I forgot to factor for bigger tires! I got aprrx 452 miles/50 gallons with the 40s.

I never timed the IP, just lined up the marks. A couple hundred miles ago I adjusted the timing a little. Apparently I was slightly retarded to the mark on the timing cover so I went a little advanced. It help some but not much. I can get some smoke to puff without much pedal but it still is never "turn the day to night" amount. About the same as the old turned up pump, maybe a little more.

Now my 93 turbo was definitely retarded. It did not smoke at all even after turning the pump up like 1.5 turns. I did find a crack in the pass manifold just before it blew the oil cooler line and locked up. I was getting about 10-11mpg with the same driving. IP was right on the timing gear mark but never actually timed. This was with new injectors and IP as well.

Seems weird that retarded it was smoking a lot and now advanced it's less on the 89. I would've thought it was too advanced at first causing smoke but then I saw it was retarded to the timing gear mark so I advanced it. I'm going to order a Ferret because both trucks needs to be timing anyways.

For now which way would be better to go with the timing in the 89? I don't mind getting 12mpg but 8 is just ridiculous. 10 was bad enough in the 93. Wish I was getting 17+ like before of course.

 

[icanfixall]

Please take this for face value.. Those "timing marks" your looking at really don't mean anything about advance or retarded timing. Every pump that installed after it has been rebuilt has a differant timing set point. So trying to adjust the timing with any pump OTHER than what came on the engine will tell you nothing. The marks are a wild ass guess WAG and thats about all they do for us. Now if a person really knows what a correctly timed and running engine sounds like they can get close timing by ear... But not even I can time by ear and I have done plenty of these engines timing. Mel admits that only once in his many years and many timing clinics has he ever got the timing by ear at 8.5 btdc. He even said he got lucky. Our engines needs to be timied by a meter to get them correct. Then they can stay timed for many thousands of miles..

 

[79jasper]

^^^^ What Gary said. To the "T"

 

[Kalashnikov]

That's what I was figuring since both trucks were opposite in regards to timing when set with the mark.

 

[chris142]

Mine was very retarded too and it really smoked. I bought the tool and adjusted the timing. Got rid of 90% of the smoke but MPG did not change.

 

[idiabuse]

I drove to Ala from Miami then let it sit 4 days without starting, I cranked it up in the cold and elevation was 500ft higher than my home, noticed a whole lot of smoke at idle. Decided to loosen pump and crank it toward the passenger side a bit. actually lined up the marks. Smoking settled down, starting is much easier, but power is down I think I have lost an injector.


Javier

 

[Kevin 007]

And when regarding the "fuel mileage vs timing" I have always found that when the timing is slightly on the retarded side; the fuel mileage is a bit better then it would be if the timing was on the advanced side...like 9.5BTDC or so.

 

[rockbender]

So Kevin007, you're suggesting that the 9-9.5 btdc may have a slight power advantage and 8.5-9.0 btdc may have a slight economy advantage?

 

[justinray]

If it's of any value, I'm running 9.2*, checked and changed ever 2 oil changes, and get 16-19mpg, since my drives are inconsistent.

And that's pushing 33X12's, with a currently poor alignment, and 4WD weight..so you should be able to get similar.

 

[Kevin 007]

So Kevin007, you're suggesting that the 9-9.5 btdc may have a slight power advantage and 8.5-9.0 btdc may have a slight economy advantage?

Yes, in my opinion anyways. Not too sure why, Just seems to be the case. I have noticed that with VW 1.6's also. I would set them at .095mm obosed to .100 as most shops like them. I got better mileage that way, easier starting and less black smoke.

 

[Black dawg]

From what I have seen, the shape of the injectors makes all the difference in fuel economy in a diesel.

In my truck I usually set timing at 5-6deg, I have had it set anywhere from 2-12, with no measurable change in fuel economy.
Anything over 6 deg, and black smoke (non gated turbo) becomes obnoxious before the turbo spools.

with a healthy engine and fuel system, you usually dont get white smoke problems until timing is less than 2 deg.

Also, there is a big difference in the timing of the actual combustion event with timing set at 8 deg (pulse timed) with perfect injectors
and at 8 deg with worn injectors. This is where timing by ear/feel comes in.

 

[justinray]

From what I have seen, the shape of the injectors makes all the difference in fuel economy in a diesel.

In my truck I usually set timing at 5-6deg, I have had it set anywhere from 2-12, with no measurable change in fuel economy.
Anything over 6 deg, and black smoke (non gated turbo) becomes obnoxious before the turbo spools.

with a healthy engine and fuel system, you usually dont get white smoke problems until timing is less than 2 deg.

Also, there is a big difference in the timing of the actual combustion event with timing set at 8 deg (pulse timed) with perfect injectors
and at 8 deg with worn injectors. This is where timing by ear/feel comes in.

This is true, if finances allow, I find it best to have injectors pop tested every other oil change, and reset timing. It really isn't that big of a deal, and I find that IP's and Injectors last longer, and I get much better mileage, so it pays for itself in many ways over time.

 

[smokinpipes]

Just adding my .02 dollars worth:
My 1-ton dually was getting usually 8-12MPG (towing / non towing) I thought I had it fairly close when I changed the IP a few years ago and plopped in some new injectors.
I, a few years later, had it timed in an impromptu timing clinic at the IDI Rally last summer, found that even though it was about a quarter thickness towards the passenger side (advanced), I was still only at 4* advanced. We bumped it up an additional 5*, and I'll admit, I was a bit skeptical at the number, and being told that running my 3.54 rear end, and a C6 trans, I should get about 15MPG... I'll be a son of a gun if that wasn't true. (Thanks again Cory!)
My truck is only 2WD, but being a crew-cab 1-ton, that alone if a bit extra weight, and I have a 105 Gallon fuel tank in the bed that is always full. So, add an additional 700-800 LBS of fuel...

 

[Kevin 007]

This is true, if finances allow, I find it best to have injectors pop tested every other oil change, and reset timing. It really isn't that big of a deal, and I find that IP's and Injectors last longer, and I get much better mileage, so it pays for itself in many ways over time.

Do you really have em tested every other oil change?? Thats a lot of wrenching and tuning!!!

 

[justinray]

Every other, unless I'm out of town working at the second, then I do it at the third, I have 2 sets of BB's, so I pull one out and put the other in, and have the out set tested and adjusted, and engine timed at the same time, then just flip flop sets when the time comes again.