fuel requirements changed on rebuilt engine

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kaeman
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fuel requirements changed on rebuilt engine

Post by kaeman »

I am wondering about something, I had to rebuild my engine, and I rebuilt it with the exact same parts as the old one, ie same cam, pistons, crank rods...heads etc. just new rings, bearings, camshaft(lifter failed ate other camshaft), I used the old tune, but change my cam sensor trigger tooth so I had to change the poll location. But the engine is hard to start.... it dies several times when cold but once it has run about 45 seconds it clears up and stays running, but my afr readings show way rich compared to the old engine. I am using the exact same tune the ran well and started easy on the old engine. I am loading my msq and a couple histogram pics. I would love to get your opinions before I change the tune a bunch. I ran the ve analyzer in megalog viewer HD and it wants to remove fuel from lots of cells in the ve table.
histogram new engine.png
histogram old engine.png
new engine full sequential 2017-04-29_17.07.37.msq
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
slow_hemi6
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Re: fuel requirements changed on rebuilt engine

Post by slow_hemi6 »

How is the engine vacuum (map) now compared to the old engine. I have pulled the top end from mine before and fixed a vacuum leak that I didn't know I had. That threw my tune out.
Find the Manuals up top under Quick links: Manuals. :RTFM:
Cheers Luke
billr
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Re: fuel requirements changed on rebuilt engine

Post by billr »

Maybe the old cam had been "eaten" on more lobes than just the one that obviously failed?
kaeman
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Re: fuel requirements changed on rebuilt engine

Post by kaeman »

I am going to say that the vacuum seems to be about the same, the old engine wasn't worn out, just had a roller lifter fail and I didn't trust that the filters got all of the metal out of the oil galleys, I didn't want to put new cam and lifters into something that might have metal shavings in the oil galleys. I will have to compare several old logs with the new ones, but on the gauge I think that the vacuum is the same or maybe a bit more, like 15 inches rather than 12 or 13 inches. I just kinda figured the refreshed engine would maybe need more fuel not less.
Bill, I would have expected that if the camshaft was bad it wouldn't breathe as good and would therefore have required less fuel...
Slow, I will check the logs made earlier and compare the cruising maps, to the one I just made and see if there are any big differences.

Thanks for looking at this it just seems odd that an engine with more friction(freshly rebuilt) would take less fuel to keep it turning, it could be that I fixed a vacuum leak that I didn't know I had, when I rebuilt the engine.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
Yves
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Re: fuel requirements changed on rebuilt engine

Post by Yves »

just to make sure, you didn't change anything with regards to fuel pressure or ignition timing ? TDC was correctly determined ?
kaeman
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Re: fuel requirements changed on rebuilt engine

Post by kaeman »

yes tdc and the rest of the timing is spot on,

After looking at and comparing older data logs and the new ones, the old engine at 2750 to 2800 rpm averaged 45.7 kpa the new engine is showing an average of 52.4 kpa at the 2750 to 2800 rpm range.

The old engine is showing a lower kPa ( more vacuum) than the new one does across the rpm ranges,

I will have to search for a vacuum leak, recheck the valve lash or I might need more break in time, the engine only has about 45 minutes of drive time on it.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
Yves
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Re: fuel requirements changed on rebuilt engine

Post by Yves »

A leak would require you to add fuel imo
kjones6039
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Re: fuel requirements changed on rebuilt engine

Post by kjones6039 »

Yves wrote:A leak would require you to add fuel imo
Agreed!

Ken
1979 Corvette - 383 CID SBC w/ Holley Pro-Jection 900 CFM TBI, 4-85 lb lo-z injectors & Walbro 255 pump
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kaeman
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Re: fuel requirements changed on rebuilt engine

Post by kaeman »

yes, I am thinking a vacuum leak would lean it out, this is running rich.... I guess that the Megalog viewer will just have to do some analyzing and I will have to do some retuning. like they say no 2 engines are alike even if they are built the same. I will just retune and enjoy my hotrod.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
slow_hemi6
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Re: fuel requirements changed on rebuilt engine

Post by slow_hemi6 »

Did you read what I wrote. I did not say he had a vacuum leak. I said I fixed a vacuum leak, ie made an improvement, so it needed some fuel taken out.
Kind of like going from an engine with issues to fresh rebuild, as is the case here.
Find the Manuals up top under Quick links: Manuals. :RTFM:
Cheers Luke
kaeman
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Re: fuel requirements changed on rebuilt engine

Post by kaeman »

I read what you wrote, Slow hemi, and I am thinking that the difference in the rebuild has probably changed the engines needs. After comparing my old logs to the ones I made with the fresh engine, I am finding the new configuration is running just a little higher kpa than the old one(about 5-7 kpa higher). I will let megalog viewer analyze the latest log and tune, then install the analyzed tune this weekend and do some more logs, and get it back to where it was just before the lifter failure..... I am hoping that taking some of the fuel out will make it start easier, when its cold.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
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