3387066_PTGairfuelcontrolfptroubleshooting

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FOREWORD

Troubleshooting the PT (Type G) AIR FUEL CONTROL FUEL

PUMP can sometimes be quite difficult, so we've made a sincere

effort to make this job a little easier.

We've discussed the most common complaints related to AFC

fuel pump. Then we've explained the step-by-step procedures

involved in the investigation, analysis and corrective action

necessary to put an AFC fuel pump back in satisfactory operating

cond ition .

Use this program in conjunction with PT (Type G) Air/fuel

Control fuel Pump Calibration, Bulletin 3387049, and PT (Type

G) Air/fuel Control fuel Pump Theory and Operation, Bulletin

3387050.



This program is designed to familiarize you, the

technician, with some of the techniques for

troubleshooting the newly designed PTG-AFC fuel

pump.

1

2. Basic steps should be followed whether you are

troubleshooting a fuel pump or any other engine

component. Listen to the complaint. Talk to the

driver and find out what the problem really is. Get all

the information. Although many complaints can be

satisfied very quickly and simply, all technicians can

recall instances in which the first conclusion

reached did not cure the trouble. In these instances,

some important item of information was not

obtained, or was disregarded.

3. When you get a complaint, make sure it is a fuel

pump problem. Also make sure the driver

understands that an engine with the AFC fuel pump

performs differently than a non-AFC engine, due to

the emission control requirements of the engine.

Here are a few things that give the same symptoms

as the fuel pump.

Troubleshooting the AFC (Air Fuel Control) portion

of the fuel pump falls within two basic complaint

areas --driveability or fuel leakage.

4.



5. Fuel leakage is defined as fuel running out of the

vent capscrew, or around the no-air adjustment

screw. Let's start with fuel leakage. This can be

caused by the AFC barrel being out of location or

damaged "0" rings on the barrel, which will cause a

heavy fuel leak at the vent capscrew. Check the AFC

barrel retaining ring to see if it is in place.

6. If it is not, remove the AFC barrel and install a

(139585) torque spring behind the barrel. Reinstall

the barrel with new "0" rings and flat retaining

ring (8-16240). Make sure the retaining ring locks in

position. The reason for installing the torque spring

is to eliminate the possibility of the AFC barrel

moving in the pump housing.

7. Before reinstalling the AFC barrel, determine

whether it is cast iron or steel. Since the steel barrels

have proven to be more reliable than the cast iron

barrel, you should always use a steel barrel. The cast

iron barrel has no identifying mark, but is slightlydarker gray than the steel barrel. There are two

vendors of the steel barrels. One has a groove cut in

the top of the barrel. The other has an "S" before the

part number stamped on the top of the barrel.

8. If there is a light leak at the vent capscrew, check the

glyd ring and "0" ring for any damage. Also checkthe plunger seal groove concentricity. This can be

done by setting the plunger in a set of "V" blocks,

with an indicator set in the seal groove. Then rotate

the plunger. Read the total indicator run-out.lt must

not exceed .0005 of an inch.



9. When installing the new "0" ring and glyd ring use

the Glyd Ring Forming Service Tool. Make sure al

parts are clean and lubricated before installing.

If you find the plunger and barrel scratched o

damaged, check the vent capscrew media. If the

media moves in the screw, replace it with a newvent

capscrew.

10.

If the vented capscrew is in a dirty environment a

better filter arrangement should be installed. A field

fix is available as a kit to replace the current AFC

breather capscrew. The benefits this will give are a

larger capacity filter, less chance of the filter

plugging, and a greater included air volume. This iintended to prevent damage to the AFC plunger glyd

ring by air-borne moisture and dirt. The kit may be

ordered as an assembly.

11

12. A new breather arrangement is now being

developed at the factory to eliminate the breather

problem. It will most likely look something like this



13. Using a clean cloth, wipe all fuel from the glyd ring.

Then, with good lighting and a magnifying glass,

visually inspect the ring for wear, scratches or

improper installation.

14. When checking the AFC barrel inside diameter a

polished appearance is normal. However, deep

scratches will cause leakage even with a new glyd

ring, and the barrel must be replaced. The AFC

plunger will show a polished appearance. Light

scratches are normal, but severe scratches require

plunger replacement.

15. A fuel leak at the no-air needle valve can be caused

by damage to the pump housing or the "0" ring on

the no-air needle valve adjusting screw. Check the

"0" ring for any damage and check the valve bore

for burrs or damage. Replace the "0" ring andremove the burrs as necessary.

16. When installing the "0" ring on the no-air adjusting

screw use the "0" ring Installation Service Tool.Make sure all parts are clean and lubricated. Then

reinstall the no-air adjusting screw. The no-air

setting must be made on the fuel pump test stand.



Let's take a look at some of the complaints you hear

about driveability. This breaks down into two

general areas each with separate complaints.

17.

18. Hard starting or engine will not start. A possible

cause is the no-air needle valve is shut off, or set with

too much fuel restriction, which wiU not allow

enough fuel to flow between the no-air needle valve,

and its seat to allow the engine to start.

This can be checked by applying 25 psi air pressure

to the AFC unit. Caution: excessive air pressure

will rupture the AFC bellows. If theengine starts, the

no-air needle valve needs to be readjusted. If the

engine does not start, the AFC is not at fault.

19.

You should also check for the possibility of a short

AFC plunger. This will allow the fuel to dump aroundthe end of the AFC pi u nger i nstead of goi ng th rough

the no-air needle valve passage. The overall length

of the plunger should be 3.340 to 3.360 inch.

20.



21 The AFC cover center die depth may be too deep, or

the AFC barrel metering groove lower edge is too

deep, which will also allow the fuel to dump around

the end of the AFC plunger. From the gasket face of

the cover to the bottOm of the die hole should be .190

to .200 of an inch.,

22 The distance from the top of the AFC barrel to the

lower edge of the metering groove should be 1.615

to 1.635 inch.

23. Excessive smoke can be caused by the fuel pump

flow exceeding the calibration specification. This

can be checked by connecting a pressure gauge to

the pump shutdown valve. Apply 25 psi air pressure

to the AFC unit. Take a snap pressure reading, andcheck the pressure against the calibration

specifications. If it is above specifications, adjust

the fuel pump on the test stand.

24. The wrong AFC spring, AFC plunger setting or no-

air setting being out of specifications can all causeexcessive smoke. Check the AFC plunger and no-air

set ti ng on the test stand. Check the color code of the

AFC spring. Adjust the AFC plunger or no-air needle

valve to the proper specifications.



The no-air setting can be checked by disconnecting

the air line from the instake manifold to the AFC unit,

and plug the line. Connect a pressure gauge to the

pump shutdown valve. Idle the engine, then snap the

throttle wide open. Compare the psi reached to the

no-air snap rail pressure in the calibration data. If

the pressure is low, the no-air needle valve is setwith

too much fuel restriction. If the pressure is high, the

no-air needle valve is set with not enough fuel

restriction, and must be reset on the fuel pump test

stand.

25.

26. Engine will not accelerate properly. Possible cause

is the air line to the AFC unit leaking, plugged or not

connected. Check the rubber grommets for

damage, and replace or tighten any loose lines or

connections.

27. A ruptured bellows will also cause acceleration

problems. The AFC bellows can be checked by

applying 25 psi air pressure to the AFC unit. An air

leak will show at the vented capscrew if the bellows

is ruptured.

Also check the vent capscrew for operation.

Temporarily remove the vented capscrew and check

the operation of the pump. If this corrects the

problem, clean or replace the vented capscrew.

28.



29. A sticking AFC plunger will also cause acceleration

problems. The AFC plunger can be checked by

removing the cover and plunger. Check the plunger,

barrel and seals. Be sure to check for dirt.

30. Slow acceleration may even be caused from the

wrong AFC setting. The plunger setting should be to

the specification. Also the no-air needle valve could

be set with too much fuel restriction. In both cases,

they will have to be reset on the pump test stand.

31. Let's look at some causes for air leakage at the AFC

vented capscrew. A damaged AFC bellows is

normally the cause of this type air leak. The AFC

Service Tool or the cover being overtightened will

fray the edges and elongate the holes. M isuse of the

AFC Service Tool can stretch the bellows. Always

index the AFC Service Tool sockets over the lock

nuts. Tighten the lock nuts and the cover mounting

capscrews to 30 to 35 in. Ibs. Before installing a new

bellows always check it for bubbles, cracks or fiber

showing through the rubber. If you find any of these

conditions, do not use that bellows.

Small air leaks can be caused bytheAFCseal gasket

(cork) missing, damaged or not compressed. Check

the gasket and replace it if needed. Tighten the nut

on the piston assembly to 30 to 40 inch Ibs.

32.



33. Small air leaks can also be caused by the teflon tape

not sealing between the plunger and nut. The

threads on the AFC plunger must be retaped if this

condition exists.

34. A low power complaint can be caused by the AFC

plunger if it is stuck in the starting position. This can

be checked by applying 25 psi air pressure to the

AFC unit and check the snap rail pressure. If the

pressure reading is the same as the no-air snap rail

pressure specification, it's a good sign that the AFC

plunger is stuck in the starting position. Remove and

check the AFC plunger and barrel for cleanliness

and damage to the seals.

35. Low power can also be caused bya ruptured

bellows, the wrong AFC spring or plunger setting.

Check the AFC spring for the proper color code.

Adjust the AFC plunger setting and change the AFC

spring or bellows if needed.

36. If the filter media becomes plugged in the vent

capscrew, a low power or sluggish accelerationcondition can occur. If the media becomes plugged

it will not let the air that is trapped behind the AFC

bellows to be relieved through the vent, and must be

cleaned or replaced .



37. If power falls off rapidly near torque peak, the AFC

plunger may be closing early. Check the AFC

plunger setting. The closing should occur at least

100 RPM below torque peak.

38. A fall-off in poweror sluggish acceleration can also

be caused by a moving AFC barrel. The barrel

should be removed and inspected for signs of

movement. If it has been moving install a new barrel

and "0" rings with a (139585) torque spring behind

the barrel, and a flat retaining ring (5-16240). This

barrel has the imprint of the retaining ring around

the edge of the barrel.

39. Now let's look at some adjustment problems when

adjusting the fuel pump on the test stand. If the AFC

doesn't repeat within the recheck limits, it is

because of high plunger-to-barrel seal movement

resistance. With the AFC plunger set to itsspecifications (:1: 3 psi), increase the air pressure to

25 psi, and then decrease the air pressure to the set

value. The difference in the fuel pressure should not

exceed 15 psi. If it does, work the AFC plunger back

and forth in its barrel several times and then

recheck.

40. If the resistance is not corrected by worki ng the AFC

plunger back and forth, check for dirt in the AFCbarrel, the condition of the glyd ring on the AFC

plunger and the surface finish of the barrel and

plunger. Replacement may be necessary if they are

in bad condition, as this plunger shows.



The no-air will not set to its specifications (:t 2 psi)

This could be caused by trying to set the no-ai

setting before the AFC setting has been made

Always set the AFC setting first and then the no-ai

setting.

41.

42. Hopefully the troubleshooting techniques outlined

in this program will aid you in locating and solving

the possible problems of the PTG-AFC fuel pump

This has been a profit from knowledge presentation.3.

3387066_PTGairfuelcontrolfptroubleshooting

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