I have a '91 4.0 and have been trying to run the self-tests. The KOEO come up with an 11 and nothing else. The engine running gives a 13 and 77. Then I tried to do the cylinder balance test and got nothing. How long should it take? I waited over ten minutes and didn't get any codes. Am I doing something wrong or is there a malfunction?

 

Hi Gumboot:

Welcome to our FTE forum

 

hhmm...
from the ford service CD...

DTC 13/411 indicates that during Engine Running Self-Test, engine rpm could not be controlled within the Self-Test lower limit band.

Make sure your not randomly pressing the gas pedal while your van is concentrating on the test it's trying to preform. There are 8 other listed reasons for this code but that's too many to list and they seem somewhat unlikely. If the code doesn't go away I list the 8 other possible reasons from the ford cd.

DIAGNOSTIC TROUBLE CODE (DTC) 77/538: SYSTEM FAILED TO RECOGNIZE BRIEF WOT(wide open throttle).
OTE:
A brief snap of the throttle may not be sufficient to pass this test. Be sure to go to WOT and return.

I believe you have to stomp on the gas for a brief moment when the computer tells you too. If you’re using the flashing check engine light to get your codes stomp on the gas after you see a single flash all by itself. I think the single flash comes after the 3 flashes which mean you have a 6 cylinder engine. Also after you stomp the gas press the brake pedal once. Some cars want you to do this so they can see if the brake on/off switch is working. Some cars want you to do this so they can see if the brake on/off switch is working. Also maybe turn the steering wheel to the left a little and to the right a little and then back to the middle. Turning the steering wheel is only needed if you have a power steering pressure switch. I don't know if aeros have those or not. I think you might be able to ignore the steering wheel step.

 

Yes! there is power steering pressure switch on all the aeros made after '88....

 

I tried it again today and made sure to get enough throttle to start the engine running test. This time it gave code 11 so that part seems to be good. I'm using the CEL to get the codes. The cylinder balance test didn't seem to work. After I tried to start it the RPM went up for a short time but then nothing seemed to happen after that. I waited 12 minutes and had no indications that the test was working. It's already running a bit rough at idle so it's hard to tell if the test is doing anything.

gumboot

 

the '91 4L Aero ECU does not support cylinder balance test....it does not use sequential fuel injection but instead uses bank injection....3 injectors/cylinders at same time

 

That is certainly a good explanation for why it doesn't work. Thanks for the help.

gumboot

 

that 4L should be as smooth as silk at idle

do the normal maintenance/service items listed on the Aero forum...do a search for details

how many miles on plugs/wires? pull all plugs and look for burned/worn electrodes, cracked insulators and carbon buildup....replace all if 1 is bad...use only double platinum Autolite or Motorcraft with antiseize grease on threads....if wires show signs of breaking down, replace with only Autolite or Motorcraft...use plenty of silicone dielectric grease on both ends wire connectors and spark plug boots....

clean/soak MAF

replace O2 sensor if more than 50k miles or unk/old rusted and corroded contaminated sensor tip

clean/soak IAC....Fords says not cleanable but many on list have some success...test center piston for free movement....pull electrical plug on IAC while idling, if IAC is working correctly, engine will stop....

run a bottle of Chevron Techron Concentrate or Gumout Regane in gas to clean injectors, intake valve tulips and combustion chambers....your bank injected 4L is worse than the newer sequential injected 4Ls for intake valve tulip fuel deposit buildup and combustion chamber carbon buildup

 

I just had the heads replaced and it isn't idling as smoothly as before. The combustion chambers and valves should be clean (less than 300 miles since replacement) and the plugs are new. I'll check the other things and see what I can find. Thanks.

gumboot

 

look for a vacuum leak in intake manifold/plenum gasket, throttle body ends, air tube to MAF...
use a spray can of carb cleaner/throttle body cleaner with tube nozzle...spray suspect areas....increase and smooth out of idle=leak pinpointed....

another test with at op. temp engine at idle.
connect a tach....pull 1 plug wire at a time....look for short duration rpm drop=100% cylinder, no drop=weak cylinder.....ECU thru IAC and injector timing will try to maintain programmed idle speed so rpm drop will be short duration....analog gauge type of tach the best.....loosen one plug wire boot at a time to test....
can also be done with fixed d.c. voltage to IAC to simulate fixed idle and ECU connector disconnected

were the injectors professionally cleaned and tested while heads off?

also suspect a leaking intake valve...happens on rebuild/regrind...valve into mismatched hole, weak valve spring from overcompression....valve stem at tulip bent....springs switched...etc...do a compression test