Head scratching timing issue

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CarlosA
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Head scratching timing issue

Post by CarlosA »

So I got my new engine back from a builder, and installed.

Jeep runs great at all times except:

In closed loop at idle.

I observed the following data:

Vacuum is 10 inches at idle - waay too low at my elevation of 500 ft on a nice day
Fuel trims at idle are negative 17,20,21% - it is pulling fuel so hard that it tries to die at idle or when slowing to stop
Compression is 135-150 PSI at 150 miles...
It has great power, good fuel trim numbers, smoothness, and economy at all other driving speeds

Cam sync was set with a DRB III and made no change. All sensors have been carefully tested - MAP, IAC, TPS, IAT, and Temp sensor are all functioning properly. New APP 985 plugs. Crank position sensor was changed for a new OEM Mopar unit to solve a different problem I had (random misfire). I also installed some 4 hole injectors because I had a couple cracked Siemens injectors. I also have spares of all the sensors on my XJ and was able to swap a few relevant ones with no improvement. Swapped coil rails. New upstream o2's, to protect the brand new pre-cats I installed.

Any ideas? If the timing set was installed being one tooth off would it still run great? It sort of has to be a timing issue, but I just feel that if the timing set is off a tooth it wont run at all. I`ll be pulling the timing cover off this week, but wanted to check in and see what everyone thinks. Further ... if the rebuilder used some mystery cam/crank is there a chance that the marks would never line up properly? Can anyone point me to ways to manually verify these things?


drb-trims.png
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SkylinesSuck
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Re: Head scratching timing issue

Post by SkylinesSuck »

Which injectors exactly do you have?

And please tell me more about the DRB III emulator you took a screen shot of.
CarlosA
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Re: Head scratching timing issue

Post by CarlosA »

I used some Bosch injectors from ebay (issue was there before also):

https://www.ebay.com/itm/SET-OF-6-BOSCH ... 1118209815

DRB III Emulator was a bit of a nightmare to get working but it is illegal chinese cracked stuff .. so if anyone gets uneasy about me linking to it, please edit this post and remove. If anyone wants to know MORE about it, and my long road of getting it working .. I can start a thread.

http://blog.obdii365.com/2017/12/02/set ... emulation/

Mine is a slightly different version than what is shown here, but they shipped it to me in 3 days with DHL, works great.
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Re: Head scratching timing issue

Post by SkylinesSuck »

I doubt anybody on here will care about cracked Chinese software if it can get them DRB III functionality on the cheap! Please start a thread when you get the chance.

What year is yours? Not saying it's your issue, but those injectors look like stock sized replacement units with the only difference bring they are 4 hole and thus would be too small, at least at WOT.

Do you have a wide band? How do the plugs look after letting it idle?
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Re: Head scratching timing issue

Post by CarlosA »

Mine is 2000. I tried those injectors and also some 28 lb 12 hole injectors. I don't have a wide band that I know of, not even sure what that is. I'm new to diagnostics and do have quite a bit of software but not a lot of experience using it.
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SkylinesSuck
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Re: Head scratching timing issue

Post by SkylinesSuck »

28 lb injectors are too large....maybe. Depends on the fuel pressure they were meant for and what you're running. But don't certainly way too big anyways.. A wide band O2 sensor will tell you the air/fuel ratio you are running and should be considered an essential item IMHO.

Let it idle then pull the plugs and tell us what they look like. Black? White? Brown? Wet? Don't drive it, just idle where the issue is.
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Re: Head scratching timing issue

Post by CarlosA »

Here is a pic of the plugs after idling for about 30 minutes. They were a little wet as always too, which is likely from the extra fuel at idle. These are with the standard 4 hole injectors. Lower right plug shows a decreased gap, I dropped it ... so ignore. All others are correctly gapped at .035"
plugs.jpg
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CarlosA
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Re: Head scratching timing issue

Post by CarlosA »

SkylinesSuck wrote: A wide band O2 sensor will tell you the air/fuel ratio you are running and should be considered an essential item IMHO.
Will look into these later, I can move my new ones downstream.
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Re: Head scratching timing issue

Post by SkylinesSuck »

If your plugs are wet from fuel, that says way WAY too much fuel to me. That can do real engine damage by washing down the cylinder walls. Do you still have the stock injectors? I would also check the fuel pressure. That's easy with a cheap gauge on the fuel rail.
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Re: Head scratching timing issue

Post by CarlosA »

SkylinesSuck wrote:If your plugs are wet from fuel, that says way WAY too much fuel to me. That can do real engine damage by washing down the cylinder walls. Do you still have the stock injectors? I would also check the fuel pressure. That's easy with a cheap gauge on the fuel rail.

The first 149 of the current 152 miles on the new engine were on the stock injectors, the problem started with those. The reason this is pulling so much fuel is because the low vacuum makes the MAP sensor believe that its under load, when it is not. As soon as you rev
off idle, vacuum goes to normal and all is good.
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Re: Head scratching timing issue

Post by jsawduste »

What camshaft and LSA numbers are ground into the cam ? What timing set ?

Your low vacuum and cylinder pressure is suggesting the cam is not degreed in properly.

The MAP in a standard cal likes 13 inches or more. Like you say it is seeing a low vacuum and increasing the injector duty cycle.

112 to 114 LSA seems to generate enough vacuum to keep the MAP happy in most applications.
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Re: Head scratching timing issue

Post by CarlosA »

jsawduste wrote:What camshaft and LSA numbers are ground into the cam ? What timing set ?
These are most likely stock pieces from the 2000-2003 era. My previous engine was a stock 2003.

I'll pull the timing cover asap and try to see what is going on there, it's been many years since I've done a mechanical time.
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Re: Head scratching timing issue

Post by SkylinesSuck »

Ahhhh, okay. Starting to put the puzzle together. Unless you have an adjustable timing set, just make sure the dots are lined up. You think it's a stock cam on a stroker build? Who put this together?
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Re: Head scratching timing issue

Post by jsawduste »

Using the dots on the timing set is folly. The only real way to know if the cam is installed/timed correctly is to degree it.
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Re: Head scratching timing issue

Post by SkylinesSuck »

For his purposes, the dots should be fine. At least as a starting point to see if it's a tooth off or something which is the only way I could see it being off enough to cause his issue. And if he had a stock cam and non-adjustable timing set it's a moot point anyways.
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