bad computer?

[r2987v2]

i have a 1998 5.4 exp with 175000 on it, full exhaust, intake, dynotune
for about a year now it has had hesitation, bucking and multiple random misfires
mostly under load, the only way i can drive it is when i hold the gears longer and shift manually (this prob happened before the dyno tune)
i've changed coils plugs fuel pump cats o2 sensors every sensor except the knock sensors the fuel filter 4 times and have run 93 from several stations
the problem is worst when the engine is cold, i have no trouble codes
my guess is the computer, any ideas?
oh yeah and it also burns a quart of oil about every 800 miles, it burns more oil than the ATF burns branch davadians

thanks for any help

 

[toms89]

Vacuum leak? May be lean misfire...

Whats the plug gap?? Plug condition??

Bad tune could easily be the source of your misfire as well..

 

[daoud el-massri]

Good after noon it could also be clogged cats something like this happened to my 4.6 it was a 2000 . Ran like crap I did coils spark plugs new cats and it ran fine for a while then the motor had no compretion .

 

[stamp11127]

Troubleshoot that puppy by checking one thing at a time noting any changes. If you make changes and there isn't an improvement then return it to the original state - undo the change.

Check the plugs for which cylinders are using the oil and make sure they are correct.
As Tom stated a vac leak will cause misfire
Check fuel pressure - it raises hell if it is low
Wouldn't hurt to unhook the cats and go for a short ride noting any difference
Check plug wires for evidence of spark leakage.

 

[Brown Bear]

partiall clog in the fuel rai? injectors?

 

[toms89]

partiall clog in the fuel rai? injectors?

Its not likely your going to have problems with the fuel rail unless it has been physically damaged.

The fuel injectors are a possibility. If debris makes it pass the fuel filter it can settle in the micro filter at the top of each injector potentially restricting fuel flow.

When the engine is cold it requires more fuel so I would be looking at fuel / air delivery issues first since you stated its more of an issue while its cold.

But there are many potential causes.

What programmer was it dyno tuned with? Can it be returned to stock to eliminate the tune as the source of your issues?? I know with SCT programmers you can choose between tunes or return to stock.

 

[r2987v2]

more info

this whole problem started 2 years ago when i hosed off the engine and went to go drive it, i changed the plugs after driving it a few months with it misfiring every mile, the plugs had carbon deposits on them after i changed them it ran like new for about 5 months
then the prob came back, so i drove it another 4 months and changed the plugs again, this time the plugs looked normal, so i changed all 8 coils for motorcraft
after i did that it ran a little better but still almost undriveable

it all happened after hosing off the engine, so i'm thinking i fried some electrical connection to the ecm?
i changed everything else imaginable on this truck

i'm almost at the point of just giving in and buying a toyota truck

 

[r2987v2]

more info

the misfires started before the dyno tune, and yes i have changed the truck back to stock tune with no luck, if i'm accelerating after it's warm and it accelerates good up to 55 mph and i drive 55 for a few miles and then stop at a light, then when i go to accelerate up to 55 again it hesitates and misfires all the way up to 55 and then it still misfires

can theses 98 ecm learn and adjust the air fuel ratio on there own?

 

[r2987v2]

by the way tom i saw you expe video on you tube, holy crap i'm speechless

 

[Brown Bear]

I agree with toms89, returned to stock and see if any symptoms persist, and it doesn't hurt to remove the injectors and give then a quick clean, I did on my durango a few montgs ago spray yhem with carb cleaner and let them air dry before installing them again, imho.

 

[toms89]

the misfires started before the dyno tune, and yes i have changed the truck back to stock tune with no luck, if i'm accelerating after it's warm and it accelerates good up to 55 mph and i drive 55 for a few miles and then stop at a light, then when i go to accelerate up to 55 again it hesitates and misfires all the way up to 55 and then it still misfires

can theses 98 ecm learn and adjust the air fuel ratio on there own?

Yes. It actually does this multiple times a second based on your upstream O2 sensor readings. Vacuum or exhaust leaks, fuel deliver, misfire or multiple other sources can wreak havoc on its ability to do this accurately though.

 

[toms89]

by the way tom i saw you expe video on you tube, holy crap i'm speechless

Thanks..

 

[r2987v2]

hey tom i'm going to change the plugs and maybe clean injectors, i've had new 02 sensors for about 8 months now, is there anyway to clean the 02 sensors?