The king demon of all 3.8 5 speed mustangs.

[Tyler vanderpan]

First id like to say this is the demon hellspawn 98 ford mustang 3.8l 5 speed
Just multiple issues... seems like when one gets taken care of another arises..


Ok hello all im new really could use some more ideas as im kinda out of them at the moment. So when i first had the car brought to me it was running rough at idle and under load. My first assumption was the vaccum lines and or IACV. It has sluggish acceleration rough idle. Now let's keep in mind that the plugs, wires were done within the last 6 months. The fuel filter was done in the last year. We checked the vacuum lines for leaks.

Initially my father thought it had a blown head gasket. So i performed the compression test. The motor passed within spec. Since i was pulling all the plugs went ahead and cleaned them all. Replaced them all and plugged the scanner in. The scanner initially came up with o2 sensor codes and whichever is the driver side system bank lean. My buddy whose been a mechanic for years pretty much told me to find the fuse for the heated o2 circut and pull it since it still had voltage with every thing off. So i pulled fuse 10 and disconnected the o2 sensors.


It had a few fuses that were blown and had copper wrapped around the blades of the fuses. I naturally pulled them and replaced them. No real change. There was extra air being allowed in from the pcv line that goes to the snorkel by the MAF. Again fixed it and no real change. So by this time i was thinking the MAF since the voltage wasnt in spec. So i went to the junkyard and grabbed three or four of them to make sure i had one that would work. With the maf changed it started to run better but then wouldnt stay running.

I figured that this might be the IACV. So this one i actually went and got a new one of. Because honestly i thought i ruined the old one when i pulled the throttle body and was cleaning it some of the gunk i thought had gotten into the diaphram making it stick and not work. Little did i know my father had broken the clip. So back to the junkyard i went to get s clip for the IACV and a few others just in case.

Well in the process of pulling the throttle body a vacuum line that was now hard plastic got broken. Yay another junk yard trip lol. Grabbed vacuum lines as well as a couple of new TPS. At this point it started to run great so we put every thing back together and were gonna be done with it haha. He goes out the next morning to start it and it would not stay started.

So i finally got my scanner back from a friend nothing fancy but enough to diagnose codes clear them and view live data.

So far the most recent code we pulled was p1506 which is something to do with the IACV which we arent really too worried about because wr dont think it has much to do with some of the major drivability issues we are having. Some of the main codes wr are worried about are p0174 and p0171 which is bank 1 and 2 too lean. Which again to remedy to try and diagnose we unplugged the o2 sensors. Seemed to run fine but then we got a p0301 code. Which im sure we all know is the cylinder 1 misfire code. So i swapped 1 and 5 at the ignition coil to see if the wire was bad. Still threw it on cylinder 1. So we pulled the plug again and cleaned it again and it seemed like there was oil on the threads which my guess was from the o2 sensor being plugged in and then the o2 sensors throwing a code from being bad. I tead somewhere when they go bad they usually throw a lean code therfore cause the pcm to continue adding fuel. It got to the point where the short term fuel trim was +30-70 and the calculated load was up in the 90s all the way up to 98 with barely even moving. So again we unplugged the o2 sensors hoping we could gain some drivability back and it really didnt seem to improve much...

So really looking for ideas on where to go with this demon mustang. We are also looking for dynamite at this point just for some satisfaction. If you have any ideas please feel free to throw them out i will respond as quickly as possible. I may have missed some info but my head is all over the place swimming with infomation on where to go with this and what to do next. Hoping tomorrow is a nicer day because this cold air sucks.. mainly in a rush /dire need to get this running right for a florida trip next week please help hahah.


Oh almost totally forgot to mention the previous owner cut the catalytic converters off and straight piped the exhaust. Only has the pre catalytic converter o2 sensors. No rear o2 sensors.

 

[6 Shooter]

Do you hear a tic tic tic noise coming from around the headers which would suggest an exhaust leak? Check first on the lean side of the motor.

 

[Tyler vanderpan]

Do you hear a tic tic tic noise coming from around the headers which would suggest an exhaust leak? Check first on the lean side of the motor.

Both sides are lean with o2 plug in changed manifold gaskets 6 moths ago

 

[Phil II]

Doesn't matter if the gaskets were changed 6 months ago or yesterday. You need to actually verify the flanges are sealed. Perfectly possible there is a gap to due warpage or a nick from an errant tool.

Why not replace the 02 sensors instead of unplugging?

If the MAF is unplugged does the engine still run lean on both banks? Or does the ecm use the failed MAF table and run a bit rich?

What color are the spark plugs?

 

[Tyler vanderpan]

Thank you for the reply I haven't fixed the O2 sensors because kind of tight on money are you talking about if I have the O2 sensors plugged in and the maf unplugged or the O2 sensors unplugged in the maf. unplugged I have not tried the opposite way around the only way I have tried is to unplug o2s with the new maf plugged in. I will clear the codes plug do o2s back in and unplug the map and see how it runs and report back. I know yesterday when I was driving I have the others plugged in and the math plugged in the car I was reporting on the short-term fuel trim extremely high etc running really rich the longer I drove it the worst it got and going up hills was definite no-go

 

[Phil II]

Ok. When the ecm had both the maf and o2 sensors reporting its possible for the ecm to operate in closed loop. Then adaptives are effective.

Specifically running the car without the maf forces the ecm to use the failed maf table. It's a very conservative fuel trim. Your car should definitely run rich in this state.

Have you pulled the spark plugs and noted the coloring? Black indicates over rich. White is lean. Brown or dirty white is just right. You need this to verify the validity of your error codes.

You might be able to score some new to you 02 sensors at the junk yard. Much like you're earlier venture for MAFs.

 

[6 Shooter]

White is lean. Brown or dirty white is just right.

White ceramics can also indicate a coolant leak into the cylinder.

 

[Tyler vanderpan]

Unfortunately wasnt able to score any o2 sensors at the junk yard. I just did a fuel pressure test and its within spec but barely. its running 32 or 33 psi while idling then kinda goes up as the acceleration is hit. the spark plugs are a different story just because i think there might be failing rings because we pulled one and it looked as though the oil was on the threads. im going to plug the o2 sensors back in and unplug the maf and see how it runs then. i was basically told the opposite that if i unplug the o2 sensors and pull the fuse to the heated o2 circut then it was revert back to a data table for the failed o2.

 

[Tyler vanderpan]

Do you hear a tic tic tic noise coming from around the headers which would suggest an exhaust leak? Check first on the lean side of the motor.

no tic tic tic id have heard that one.

But this mustang is ridiculous cant climb any hills absolutely no power left in it hah. its bad to drive and unfortunately have to keep driving. i think 3 times i was close to what was wrong with the damn car and it ran fine for about 15 minutes then keeps reverting back to this bullshit lol.

 

[Phil II]

What was your cranking pressure when you checked head gaskets? That would indicate of the rings aren't up to task anymore.

 

[DanF]

Only thing I can say, is kinda had the same problem in my 98, I got the safety star bit's, cleaned my MAF with alcohol, and my Problems went away,,I live in Florida, on the Atlantic, I guess salt air takes it's toll..LOL..good luck to ya..