Air Fuel Mixture Logic

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jstric01
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Air Fuel Mixture Logic

Post by jstric01 » Sun Dec 28, 2003 9:57 am

Hi All:

I am in the process of fixing all the teething problems of bringing up a new engine for my Federal 82 Vanagon (2.0L type IV engine). I am still in the process of trying to get the engine to idle well and set the air fuel mixture. I am looking for some suggestions or comments on
my reasoning process.

Current situation:
- the FI system checks out and fuel pressure is to specification.
- valves were readjusted (after they pumped up) and compression is now 110-120 in all cylinders,

Problem: Can't get the car to idle well enough to set the timing using a timing light or the mixture using a O2 sensor.
- To start the engine I have the timing statically set at 7.5 BTDC.
- Idle mixture screw 8 (half turns) open and the CO mixture screw mostly closed. These were the settings from my old engine.
- The car will immediately start but will need the throttle to be held open to continue to run (at about 1500 rpm). If I do not hold the throttle open the engine will die. Vacuum at 1500 rpm is about 15 InHg.

By my reasoning, I am running too rich so I need to give the engine more air. I have tried opening both the idle screw all the way and
leaning the mixture at the AFM. This improves thing slightly, but still requires more air (by opening the throttle). If I now vary the timing I
can get the engine to idle (poorly), but the timing must be advanced around 16-20 to get this to happen. Vacuum decreases when I do
this.

By opening the throttle I am also delivering more gas. So maybe it is not the mixture at all but something to do with the injector spray pattern. I have not checked this since the old engine was removed, but a year ago they gave me a nice conical pattern. They were stored dry as not to gum up.

So what does the community think the initial problem is? Any ideas on how to proceed?

Thanks for the help in advance.

Regards,
--Jeff Strickrott
82 Westy, South Florida

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raygreenwood
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Post by raygreenwood » Sun Dec 28, 2003 12:14 pm

A lot of things to check. First...what is your fuel pressure. You have a vacume assisted rising rate regulator. If there is a single vacume leak anywhere...you will be running very rich. Check everything for leaks. Runner boots, injector seals, TB to manifold seal, valve cover gaskets, oil breather gaskets, PCV...if you have one. Check your vacume hose routing. It should be at 28-32 idle fuel pressure and about 36 when the throttle is opened. Also, check the reistance on the cylinder head temp sensor. Ray

jstric01
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Post by jstric01 » Sun Dec 28, 2003 7:39 pm

Fuel pressure is 36 psi when the vacuum hose is disconnected, 29-32 when the engine idles. As I rev the engine fuel pressure becomes 29 psi.

I have removed/plugged the air lines for aux air valve, the deceleration valve, PVC valve, and brake vacuum line. Again everything else is new, hoses on manifold, air boot to throttle body, injector seals, up to including the shaft seal on the throttle body. Squirting WD40 on the injector seals and intake manifold indicating no leak there (so much for the clean paint job).

When I set the timing by ear and by what provides the best vacuum (13 InHg), I still end up with timing that is too advanced from what it should be (7.5 BTDC), greater than 20. The engine dies if I ever try to set it near 7.5 BTDC. Vacuum gets around 15-17 InHg when I rev the engine to 1500 rpm.

So I have low vacuum for a new engine (assuming no other obvious leaks) and I need the timing advanced for the engine to idle. Any idea what is wrong? Valves have been adjusted to 0.006" per Bob Donald's page on hydraulic lifters. Compression cold was 110-120, warm it is around 130-140.

My next check is to test the spray pattern on the injectors. AFM passes the test along with head temperature sensor.

Regards,
--Jeff Strickrott
82 Westy, South Florida

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raygreenwood
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Post by raygreenwood » Sun Dec 28, 2003 7:54 pm

The answer to your problem is in your post. The fuel pressure vacume line is attached to the wrong point in the manifold. When the engine is idleing, it should be at the 29-32 psi figure. When you rev it...it should go to 36. You listed that revving it makes it go to 29. That is backwards. It means hat at idle you are horribly rich. No amount of idle compensation will correct for this amount of fuel. When you rev it up....it leans out because vacume is drawing on the diaphram...causing it to pull against the spring pressure that allows higher fuel pressure. So...when you rev it...it runs lean. That will act just like an advance problem when you are not suspecting a fuel pressure problem.

The regulator works by having high vacume draw the diagram back against the spring at idle. This causes the pressure to drop. When you open the throttle, the vacume goes to near "0". This causes full spring pressure to be exerted on the diaphram...which has a polished plate that covers the fuel inlet to the regulator. Its like putting your finger over the end of a hose...the pressure goes up. Ray

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amskeptic
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Post by amskeptic » Tue Dec 30, 2003 12:54 am

The answer to his problem is also in his original post. When you close the CO screw you are enriching the mixture. That CO screw is merely an air waste gate around the airflow metering vane. As you close down the screw( i.e. right CW), the air is directed fully to the vane richer. Turning *out* the CO screw allows air to bypass the vane undetected, this will lean it out. Also, the fuel pressure regulator does not give you a black/white measurement if you attempt to check it under running conditions. It will only give you 36 psi under full throttle under load. Fast low-load engine operation will have too much vacuum and will moderate the pressure to the readings you observed. Pulling the hose off was the correct test, and your regulator responded appropriately.
Colin

danfromsyr
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Post by danfromsyr » Tue Dec 30, 2003 12:12 pm

another answer that is also in your post.
you have the decelleration valve blocked.. but did you also eliminate the hose from the air intake to engine breather tower?

mine was leaking and capped by the PO the breather tower to air intake hose is >after< the air flow meter, so that hose diameter is preprogramed and will run rich w/o being hooked up.

it's likely a combination of the above mentioned issues. as usually any just 1 wouldn't cause more dire richness issues.

GL
Dan

jstric01
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Post by jstric01 » Tue Dec 30, 2003 11:39 pm

Thanks for your feedback so far.

To recap:

1. The pressure regulator was connected to the air box (not the throttle body) per the FI diagrams and does regulate as required. If the engine had 15 InHg or more of vacuum at idle then the pressure regulator would deliver fuel at 29 psi, but as the best I can get is 13 InHg of vacuum, the manifold pressure is not enough to completely control the fuel pressure.

2. All the extraneous hoses (aux air, deceleration and the case breather vent) where removed and blocked to see if they were the cause of the low vacuum. This was not the case as vacuum remained constant at 13 InHg. I did not think they would be the source as everything rubber is new and these components worked fine in the old engine. Plus, the new engine runs the same with the hoses blocked or connected. The air box and manifold connections passed the “WD40 test” and no large vacuum leaks were detected.

3. Cylinder compression is 135 (engine warm) in all cylinders. Valve lash is set to 0.006” (even though the valves are hydraulic) to help work out any of the air that is in the lifters. Preload will be applied after no more noticeable compression on the pushrod is detected (see www.bostonengine.com for procedure).

4. In order for the engine to idle at 900 rpm, I need to have the timing advanced to 28 BTDC, the idle screw 12 (1/2 turns) open and the CO valve closed. I can run the engine at a higher rpm with these conditions changed (how I ran the engine during cam break-in at 2000 rpm), but I cannot get it to idle in any other situation.

My two questions are:

1. Why is the timing so advanced?
2. Why is the engine vacuum so low?

For background on the engine:
1. It has new AMC head with new valves.
2. New Mahle pistons and cylinders.
3. New lifters and stock hydraulic grind cam.
4. Every seal/gasket or anything else rubber has been replaced (including the seals on the throttle body).
5. New O-rings on the PVC vale (so it does not leak).
6. A good OEM oil pump, no scoring on the case or gears.
7. No leaks at any seals/gaskets.
8. New oil cooler.
9. All my aux air valves are reconditioned (valve functions smoothly, no rust or dirt). All other FI components check out to specification.

I have verified my cam/crank timing and it is in correct alignment. The distributor drive gear is where it should be. I am using the stock OEM vacuum/mechanical advance distributor. The injectors do not leak and have a “fairly ” conical spray pattern. I say fairly as I have never seen an ideal cone from an injector so far. I have two good (never modified, good resistors paths) AFM’s and I get the same response from both. And yes I have connected the plug wires to the right locations. I am running a Pertronix Ignition system, so the point gap is not an issue.

What I will do next:

1. To solve the criticism of having the fuel pressure regulator providing too much gas I can just connect it to a vacuum source to get 29 psi and see how the engine performs at idle.

2. I will perform a leak down test to see if anything unexpected is leaking (manifold, air box, heads, etc.). But other than these simple steps I am at a loss as to what to try next.

Can anyone explain why the timing must be so advanced? What would you try next?

TIA
Regards,
--Jeff Strickrott

Volcano
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Post by Volcano » Wed Dec 31, 2003 7:29 am

Hi Jeff; The vac hose for the reg goes to the throttle body not the air box.Dist. also.Check out your timing light.Mine has a knob on the back.Make sure it's at 0.Just a thought.Regards

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amskeptic
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Post by amskeptic » Wed Dec 31, 2003 9:19 pm

jstric01 wrote: Can anyone explain why the timing must be so advanced? What would you try next?
--Jeff Strickrott
Camshaft incorrectly indexed to the crank? Low vacuum and goofy compensated timing would be a result. . . .
Colin

jstric01
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Post by jstric01 » Fri Jan 02, 2004 2:57 pm

I verified my crank/cam alignment by seeing when #3 exhaust valve just closes and #3 intake just starts to opens. This happens when #1 cylinder is at TDC. From my calibrated eyeball this is about 1 degree off of where I have marked TDC on the flywheel. I had determined TDC when the engine was out.

According to Bentleys, the fuel pressure regulator and deceleration valve both get their vacuum from the air box, not the throttle body. But thanks for the suggestion.

The only time that the engine runs at idle close to spec if when I inadvertently had the AFM harness connector disconnected. Thus with low/almost zero fuel pressure, as long as I did not touch the throttle the engine would idle close to 10 BTDC.

So does this mean the engine is running way too rich when I have the AFM in the loop?

With a 15 InHg vacuum source connected to the fuel pressure regulator (that is fuel at 29 psi), I still have the same symptoms (will idle only with advanced timing and as much air as I can give).

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amskeptic
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Post by amskeptic » Fri Jan 02, 2004 8:09 pm

Your symptoms are not adding up to any logical conclusion. I would set your valves to .000 which isn't quite where the lifters want, but it will improve your intake efficiency a bit. There is no reason for your engine to be so anemic, with the compression figures cited and your allegations of correct valve timing. I would like to reiterate that you lean the mixture out by *opening* the mixture screw on the airbox, that's counterclockwise as you face the screw. Find a vacuum source at idle, anything under the throttle plate but the brake booster, and pull it off. Does the idle speed up? Turn that screw out until the pulled hose trick causes the idle to lope or even drop a little. If your idle keeps speeding up when you add air, even when the mixture screw is wayyy out, then you may have that unusual condition where the big spring on the flapper has caused the plastic wheel with the indentations to sort of strip and unwind the spring like a busted old alarm clock. Test with a different air box to see if your mixture/idle improves with a different airbox. You might very well have a problem with the airbox, which also houses the ambient air sensor which can go south and assume every day is below 0*. That'll make it run rich also. Other than that, I'm stumped and ever more grateful for my elegant and simple original equipment dual Solex carburetors.
Colin :D

regis101
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Post by regis101 » Sat Jan 03, 2004 1:51 am

Chimin' in. Fuel , fire, and mechanical. You seem to feel confident about the fuel system. You stated that the engine is new and you confirmed the valve timing. That leaves the Fire. With or with out the vacuum hose(s) hooked up properly, I would think that it should still run decently. You have not discussed the condition of the dizzy. Have you checked it for shorts, or binding? Was the pointless pick-up installed during the old engines life? Have you ohmed out the coil. Or better yet, varified that the black wire is on terminal 15 and the green wire is on terminal 1? Pertronix? Red to 15 and black to 1, if memory serves. Just some thoughts

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raygreenwood
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Post by raygreenwood » Sat Jan 03, 2004 5:32 pm

Don't worry about what the vacume gauge tells you right now. Its not that important. It will also read slightly different than some cars, because there is a lot of overlap in stock FI cams. By the way...what cam is installed? Also you MUST use a timing light to set the timing on type 4's...period. They should be set at 27 BTDC @ 3500 rpm. Do it with hoses disconnected...but then check it with hoses connected to be sure it does not go too far. Also...are you using the dual advance unit? If so, be sure that the vacume and retard sections are hooked to the correct area of the manifold.

The pressure regulator MUST be connected to the center plenum. It usually tee's in between two of the runners. You do not have options on where you take your vacume from. Its source is specific. If its taken from the wrong area, the fuel pressure will be highly variable. It must also not be Tee'd into other units, like the vacume advance/retard or the deceleration valve.

The previous information about valve adjustment is quite importanat. You shouldhave no gap set on your hydraulic lifters. Look for other posts on adjusting them. The book adjustment is 100% wrong for these. That is a universally held and proven opinion. But...having a gap of .006 will seriously mess with your vacume readings and timing. Ray

jstric01
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Post by jstric01 » Fri Jan 09, 2004 1:08 pm

Hi All:

Thanks so far for all the advice and an update from the trenches on what I have done and where I am.

Timing:
I wanted to be really sure about the cam timing, so I degreed the cam to see when the valves open and close. I have included an image at (http://www.cs.fiu.edu/~jstric01/images/Valve.jpg). If I use 0.015 for when the valves open I get: Intake Opens at 28 BTDC and closes 70 ABDC, Exhaust opens 68 BBDC and closes at 18 ATDC. That gives duration between 266 and 278 with an overlap of 46 degrees. Remember this was done with the engine and the lifter in the car, though I picked up the outside of the lifter body to avoid errors due to lifter compression, so it is probably not that accurate. Accurate enough I hope to indicate that the valve timing is close to where it should be; that the cam is not off one tooth.

Image

Vacuum:
I took the induction system off and found that one of the injector seals was leaking (the new paint on the intake runners caused a bad seal), and the new air box/throttle body gasket did not seal as well as I though it should. Form my collection of new gaskets I found one that fit the best and used Blue RTV to make sure it did not leak. Before installation the complete induction system would hold a 15 InHg vacuum until the duct tape on the intake manifold leaked (5-6 minutes). During stages of reassembly I was able to pull and hold a vacuum (for 30-40 seconds). When completely installed with the intake boot plugged I could achieve (using the starter to turn the engine over):
· 15-17 InHg with aux air valve, deceleration valve and all vacuum lines connected but with PVC and brake booster plugged,
· 13 InHg with PVC connected but brake booster plugged.

Ignition:
I have two rebuilt distributors, new ignition coil and Pertronix electronic ignition. Plug wires are new. I do not detect and binding or other sticking with the distributors.

FI:
- Cold start valve works (does not leak),
- Aux air valve works,
- Wire harness and grounds in good shape (buzzed out from ECU connector),
- Cold air timer (real name?) works,
- Injectors: 1 leaks but is within the 2 drips per minute test, all spray conically and put out approximately the same amount of fuel. Now I have read that the spray pattern is supposed to be very fine (misty), but mine appears to not be. So injectors will be added to the things to get list.
- AFM passes the simple test in Bentleys.
- Both temperature sensors read within their respective ranges.

Valve Lash (history):
After running the engine for 20 minutes (during the first part of break-in) and 5 miles, I adjusted the valve cold for 0.006” (per Boston Bob’s hydraulic valve procedure at www.bostonengine.com). #1 and #3 cylinders reading around 90 psi on compression prompted this. After the adjustment, compression read 110-120 psi cold and 135 psi warm. I figure that as the engine had sat for 1 ½ months before installation that the lifters had bled down and trapped air. After I run the engine more then I will adjust the preload on the valves.

Status:
After all of this work the same symptoms exists:
- By ear the engine runs best with timing between 20-28 BTDC (measured with timing light),
- It is not possible to set timing anywhere near factor spec of 7.5 BTDC.
- I can achieve a bad loping idle (800-850 rpm) with the idle screw all the way open and CO screw all the way closed. Engine runs better with the throttle held slightly open.
- Looking at the plugs they are black with carbon after just a short period of running, indicating that the mixture is too rich or spark too weak. I am running the recommended Bosch plugs of W8CC.

When I contacted the engine builder and told them of my findings, they stated that the vacuum is normal (13 InHg at idle) and they think that my problem is with the AFM; that I need to adjust the spring tensions. I am hesitant to do this as my AFM’s (I have one California and one federal version) still have the original silicone rubber sealing them shut. The federal version worked fine on the old engine until I dropped a valve seat. Both AFM’s behave exactly the same when installed.

I still don’t really understand why a rich mixture would account for the timing needing to be so far advanced? Could it be that the installed cam is not the correct profile for my FI system?

The builder could not tell me what the cam profile should when I called and the only information I have for the stock hydraulic grind is from CB performance (IO 26 BTDC, IC 54 ABDC, EO 60 BBDC, EC 20ATDC, duration 260 and overlap 46). My curves are similar and I hope that the differences are due to errors in measurements.

I have not yet done the suggestions with removing a vacuum line to add air and see what happens suggested by Ray. I will try that this weekend when I re-install my rockers. The original fuel pressure regulator was sharing a vacuum source with the deceleration valve (they were T’d), but I will disconnect the deceleration valve for now. The vacuum source comes from the air box between two of the intake manifold runners.

I have a third federal AFM that needs to be rebuilt (worn resistor tracks) and I will experiment with changing the spring pressure on this one and see if the engine performs any better.

Ray: regarding adjusting the hydraulic lifters, what do you run and what is your adjustment procedure? I have read everything from running 0 lash to 1½ turns. The opinions seem to vary wildly. What is the best adjustment for longevity? When degreeing the cam, the lifters still feel spongy so I am sure that they have some trapped air.

I will get back with more status information on Sunday.

Regards,
--Jeff Strickrott

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