temperamental 5.0

[rogerbslee]

My 92 LX has a maddening intermittent engine problem which no garage has been able to diagnose. Basically it goes great for a period of time (often several days) then inexplicably starts running as if its lost about 50% of its bhp only to recover again later. No obvious misfire or anything during its off days just runs like 2.0 not a 5.0. Has anyone experienced anything like this?

Roger

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

After you have dumped the codes and fixed them, do a cylinder balance test.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 99 for everything OK, or the number of the failing cylinder such as 22 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures. Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure

 

[rogerbslee]

Several garages have done diagnostics on the car and found no stored trouble codes....

 

[jrichker]

Several garages have done diagnostics on the car and found no stored trouble codes....

Do the cylinder balance test when the engine is running poorly. What you find might suprise you.

 

[HISSIN50]

JR is right. there is an extra step or two involved in the balance test (from just retrieving KOEO and KOER codes - i might wonder if a shop actually performed the test - very neat little test too).

also is there anything specific about the times it runs like poo, and then when it regains its composure? i.e. when the ambient temps are very hot it poos out, and when it is cooler it runs better, etc.

good luck.

 

[90mustangGT]

Run a fuel pressure gauge and put it someplace where you can watch it and see what the pressure does when the car is cutting out.

 

[rogerbslee]

Temperamental 5.0 follow up

The local expert "Indy Mustang Performance" in Indianapolis tested the car during what i considered an "off" period and pronounced it pretty good for a 5.0. They'll never convince me because I know how far short of its potential the car is running and i would love to have it dyno tested to prove my sanity but I think I have had all the frustration I can stand with the car so might try swapping the motor for a 351 to see if that makes me any happier.
Thanks for all the comment.

 

[jerry beach]

Did you know that the engine will have more power when its cooler outside? It will also have more power when the engine is cold (just been started), but it is unwise to get on it hard until it is warmed up, unless you like to damage rod bearings and such. Can you feel the power coming and going sometimes when you accelerate? If the AC is on, it will cause this symptom, the compressor is kicking in and out. I feel that big time in mine.

Also is this an auto or stick car? If its an auto the trans fluid may be getting too hot sometimes, causing your loss of power. An external trans cooler would keep the temps down in there. Good luck with it, and keep us posted if you have any new info.

 

[dastang2]

my 95 does this but it starts messing up every 5 minutes, i have a little gauge that i can pop on the fuel rail and test the psi and when it starts running bad i look at the psi and idle it stays at like 29 (bad) and when revved it drops to about 5 psi. i bought a 190lph fuel pump but it still has not come in, check your FP. also when it starts messing up, i can kill the engine and turn it back on and it will run better