Vacuum deficiency........probably (?).

[boyt911sc]

The start up for this newly rebuild engine is not going anywhere and would like to seek ideas, suggestions, tips, etc. to get to the bottom of the problem. The initial start up was scheduled in late spring and never got it running as of this writing. A few days ago, it was discovered that the new engine wire harness has a wiring defect which causes the FP not run via the AFS (air flow sensor) switch. This wiring problem will be addressed separately. By eliminating the use of the air flow switch, I could make the FP run now but found another problem preventing the fuel distributor from delivering fuel to the injectors.

Problem as observed:
The AFS (air flow sensor) plate does not move up at all during start or cranking. Due to this observation no fuel from the FD is delivered to the injector lines.

The common course of action is to test the vacuum of the system and that's what I did. The whole CIS unit was removed and pressure tested. While under air pressure, soapy water was applied all over the unit to detect any sign of air bubbles.


After the pressure test, the whole unit was carefully installed back on the engine and did another pressure test.


After everything was put together, another attempt to start the engine was made with no luck. Fuel was not coming out of the fuel lines (fuel injectors removed for this test).

Below are some of the CSV's I got from the different CIS units I purchased over the years and used some of them as replacement and spare parts.


It is very frustrating and disappointing when you fail something you do with ease and confidence in the past. Usually, I would spend several hours to get a CIS engine to run but not this time. So I contacted a few guys in this forum to help me get back on track. I am sure there is something maybe not obvious that I have over looked or missed. So feel free to make suggestions, comments, anything that could direct me to the root cause of the problem/s. Thanks.

Tony

[tom1394racing]

Tony

Does the AFM meter plate move freely by hand? With the fuel pump running, do you get fuel pressure in the injector lines if you manually lift the meter plate? Are you sure the plunger in the fuel distributor is not stuck?

[boyt911sc]

Originally Posted by tom1394racing

Tony

Does the AFM meter plate move freely by hand? With the fuel pump running, do you get fuel pressure in the injector lines if you manually lift the meter plate? Are you sure the plunger in the fuel distributor is not stuck?

Tom,

The FD plunger moves up and down freely. As a matter of fact, when you remove the FD from the metering unit, you have to pay attention that the plunger does not drop to the floor. With the FP running, lift the AFS arm and fuel is delivered to the injectors. But I could not make any fuel delivery while cranking the starter. Unlike my other car, the AFS arm moves up and down (oscillates) slightly when you crank the starter (FP relay removed). The difference I noticed between these two (2) engines was the movement of the AFS arm. The good running engine in my car shows movement or oscillation of the AFS arm during cranking of the starter while the problematic engine shows no movement at all. The AFS arms for both were tested for resistance and basically very similar in characteristics.

I would be removing the complete CIS again and test it again with and without the throttle body installed. I noticed something about the TB but not sure if is part of the problem but without testing it, I can not eliminate as a possible culprit. I have installed a second FD and still no luck. Another metering unit is next.

Do you have any other idea or thought that could be cause of the problem? Vacuum or air leak, leak down test, poor battery, bad fuel, etc. Thanks.

Tony

['78 SC]

If you open the throttle slightly while cranking, does the FD plate move? Maybe an issue with the AAV and AAR not bypassing enough air? You may want to disable the ignition for this.

[boyt911sc]

Originally Posted by '78 SC

If you open the throttle slightly while cranking, does the FD plate move? Maybe an issue with the AAV and AAR not bypassing enough air? You may want to disable the ignition for this.

I removed the spring for the throttle body butterfly just to see if opening the butterfly would affect the movement of AFS arm. There was no movement at all of the sensor plate (?). Yes, I did disable the ignition coil during some of the tests. AAR and AAV added to the list.

Another thing that came to mind were the oil restrictors on the vacuum hoses going to the tank. Thanks.

Tony

['78 SC]

This is a new rebuild, have you confirmed the motor is pumping air? Valve timing and valve lash good? Air coming out the exhaust? If it is moving air and there are no leaks in the induction system, the air has to be flowing through the FD venturi, right?

Sorry I'm grasping at straws, but you're too knowledgeable to miss anything easy or typical.

[boyt911sc]

Originally Posted by '78 SC

This is a new rebuild, have you confirmed the motor is pumping air? Valve timing and valve lash good? Air coming out the exhaust? If it is moving air and there are no leaks in the induction system, the air has to be flowing through the FD venturi, right?

Sorry I'm grasping at straws, but you're too knowledgeable to miss anything easy or typical.

Yes. The engine is newly rebuild top and bottom. I have inspected the ignition timing using an inductive timing light and the signals were spot on @ Z1 for cylinder #1 and ignition distributor rotor pointing to the scribed mark. Valve adjustments were done months ago and was rechecked again. Also did compression test for cylinders #1 and #4 @ 160 psi. One thing I have not re-checked this week was the 964 cam timing @ 1.26 mm.

I expect some sort of suction from the throttle body to get the AFS plate to move up. I am thinking of isolating the two (2) hose breathers connected to the CIS intake boot ("pope") or test the throttle body's suction force during cranking or start.

I had done numerous engine rebuilds and starts in the past. They usually took an hour or so to get it running. But this one has been on the test stand since early spring but I have been away several months too. Any suggestions are welcome. Thanks.

Tony

['78 SC]

Good compression so it's pumping air. The induction system bench tested ok so no leaks there. Something has to be open so air is getting in without going through the FD venturi. Maybe an opening in the crankcase vent system, oil breather or a missed hose connection?

Think it's time for a full-scale leak test? Here's the setup I used to locate vacuum leaks recently. I tried this after your posts here convinced me pressuring up the whole system would work. Thanks for the advice. It never would have occurred to me the whole motor is tight enough to pressurize and leak test with soapy water. I found 4 leaking injector sleeves and a mis-connected WUR vent with this contraption.

[tom1394racing]

Tony

What about disconnecting an intake runner and plugging the vacuum end of a shop vac into the open port on the air box. See if the meter plate moves under shop vac suction. Might help to isolate the problem.

[fanaudical]

That is a weird one.

EGR on this one? Is the EGR valve blown/wide open/leaking enough air to bypass the AFS?

A quicker variant on Tom's suggestion may be to connect the shop vac right to your tail pipe and crank the car over. That should definitely get the AFS arm to move...

[tom1394racing]

Have you tried to start the engine with some starter fluid spayed into the intake snorkel? It might get the engine to fire and get the AFM meter plate moving.

[boyt911sc]

Tom,

I've never used starter fluid before with the other engines but not for this one. What helps is lifting the AFS plate with the FP running for a second or two. It would backfire and stall after a very short burst of life. The AFS plate never moved a bit that shows that the FD distributor was not activated.

I will be doing the shop vac test you suggested and I really like it. Will keep you guys posted later today. Thanks.

Tony

[jrhb]

With this vacuum leak tester setup how much pressure would you use? Thx.

Originally Posted by '78 SC

Good compression so it's pumping air. The induction system bench tested ok so no leaks there. Something has to be open so air is getting in without going through the FD venturi. Maybe an opening in the crankcase vent system, oil breather or a missed hose connection?

Think it's time for a full-scale leak test? Here's the setup I used to locate vacuum leaks recently. I tried this after your posts here convinced me pressuring up the whole system would work. Thanks for the advice. It never would have occurred to me the whole motor is tight enough to pressurize and leak test with soapy water. I found 4 leaking injector sleeves and a mis-connected WUR vent with this contraption.

[boyt911sc]

Originally Posted by tom1394racing

Tony

What about disconnecting an intake runner and plugging the vacuum end of a shop vac into the open port on the air box. See if the meter plate moves under shop vac suction. Might help to isolate the problem.

Tom,

I did the shop vac test on the air box to determine if the AFS plate would move. See attached picture.



Two separate tests were done using the shop vac with zero control fuel pressure and 25 psi. Both conditions showed that the AFS plate went up during operation of the shop vac. mimicking a running engine creating suction (vacuum) at the intake.

The shop vac attachment on top of the air box was removed and used the starter to crank the engine. Both conditions with zero control pressure and 25 psi. failed to move the AFS plate even a bit. This test clearly demonstrated the lack of suction created by the engine (?). At this point, it is not evident which is the culprit and further investigation to follow.

Tony

[boyt911sc]

Originally Posted by '78 SC

If you open the throttle slightly while cranking, does the FD plate move? Maybe an issue with the AAV and AAR not bypassing enough air? You may want to disable the ignition for this.

Since I have tested both the AAR and AAV before, I was a bit reluctant to test them. But common wisdom prevailed this morning and decided to take a look at them. To my surprised, I found fuel inside the AAR!!!!! Yes, gasoline inside the AAR. In all the years I've been tinkering with CIS, I never heard of gasoline inside an AAR.

Not only was the AAR flooded with gasoline, the bottom section of the 4-point (claw) vacuum hose (see picture below) was filled with raw fuel.

.

Further investigation revealed a defective CSV (cold start valve) that was injecting a lot of fuel and not in mist spray pattern but as a jet of fuel. The combustion chambers will be inspected to determine if there are raw fuel present (?).

Work was suspended temporarily because the grandchildren were getting ready for Hallowen treat & trick with 'Grumpy'. To be continued.......

Tony

[Walt Fricke]

The problem with the CSV, plus all the sucking and blowing, could explain why fuel moved from the air box into these otherwise fuel-less hoses and tubes and places.

Doesn't explain why cranking wouldn't move the AFS plate, though.

My thought was a massive leak in the boot connecting the two sides. But that seems unlikely generally, and specifically because your vacuum test got the AFS plate moving.

What if you plug off the connection between the oil tank and the boot? Just leave the tank open to the air. Or route the hose from the tank (not the one to the crank case - the other one) to the rear of the engine so you can see what it is doing when you crank.

Is it possible that some rings are so poorly seated that a lot of excess pressure is created, and it supplies so much air that the AFS plate doesn't need to move? Or, for that matter, is positively held down?

How about doing a leakdown on all the cylinders, along with a compression test on all of them?

That is, if you didn't eat too much of your grandkids candy.

[boyt911sc]

Originally Posted by Walt Fricke

The problem with the CSV, plus all the sucking and blowing, could explain why fuel moved from the air box into these otherwise fuel-less hoses and tubes and places.

Doesn't explain why cranking wouldn't move the AFS plate, though.

My thought was a massive leak in the boot connecting the two sides. But that seems unlikely generally, and specifically because your vacuum test got the AFS plate moving.

What if you plug off the connection between the oil tank and the boot? Just leave the tank open to the air. Or route the hose from the tank (not the one to the crank case - the other one) to the rear of the engine so you can see what it is doing when you crank.

Is it possible that some rings are so poorly seated that a lot of excess pressure is created, and it supplies so much air that the AFS plate doesn't need to move? Or, for that matter, is positively held down?

How about doing a leakdown on all the cylinders, along with a compression test on all of them?

That is, if you didn't eat too much of your grandkids candy.

Walt,

It has been a while since I did a leak down test and will locate the tools and perform some measurements. Any more ideas even how wild you think it could be? I am glad you joined the discussion because you have a very creative mind and some of your analysis were amazing. You are gifted and we are fortunate to have you around. Thanks.

Tony

[tom1394racing]

Tony

It seems the CSV is spraying fuel into a reverse airflow that's sending fuel into the bypass air tubes and forcing the meter plate closed. Is it possible that the engine is actually pumping air backwards from the exhaust into the inlet runners?

What if you remove one of the intake runners and hold you hand over the intake port on the head while you crank the motor? You should feel suction. If not, then you cam timing may be way off.

[boyt911sc]

Originally Posted by tom1394racing

Tony

It seems the CSV is spraying fuel into a reverse airflow that's sending fuel into the bypass air tubes and forcing the meter plate closed. Is it possible that the engine is actually pumping air backwards from the exhaust into the inlet runners?

What if you remove one of the intake runners and hold you hand over the intake port on the head while you crank the motor? You should feel suction. If not, then you cam timing may be way off.

Tom,

I have not checked the cam timing since I did them last winter. And will do that next plus checking the intake suction at the intake runner/s. Something is very wrong or over-looked that causes the engine to loose its suction (?) while cranking and willing to investigate all sort of ideas and suggestions to get to the bottom of this weird problem. Will update you guys ASAP. Thanks.

Tony

['78 SC]

Tony, did you confirm there is air flow from the exhaust while cranking? Your compression numbers show the motor is pumping air but is it flowing the right direction? Maybe the cams were swapped? (You said you want out of the box ideas).