Need some help from Stangnet's best

[1987stangman]

Ok guys. I can usually figure out my own car problems pretty quick, however, I have an issue that has so far stumped me with my 96' GT. The car has a full PI engine of 04' vintage. The swap was done by me around March and has a custom SCT tune and has been running great since last Thursday when I got in it to go to work. Started the car and it's got a noticable engine miss and is really noticable when driving to the point I turned back to the house to park it and drove my other Mustang to get to work. I didnt mess with it until Saturday. I changed the plugs since they were the factory ones (engine I put in had 67k) abd I bought news ones some weeks ago. I figured it wasnt the issue but I did it anyway. I also did a compression test 150-160 accross the board.

The worst part about this is I am getting no CEL at all. Nothing. The ECM is pretty good about picking up miss fires not this time. I have brand new FRPP wires on it and new 24lb injectors. I have check for vac leaks, loose grounds and even returned the car back to stock via the SCT.

I had my two old camshaft and crank shaft posistion sensors from my old NPI engine so i installed the camshaft posistion sensor with no change. Ran out of time tonight for the crank sensor. Like I said car was running perfect until Thurday morning. I know it's hard to answer a question like this but I'm stumped as hell on this one!

EDIT: The car is running rich too

 

[joshjwc9]

Can you plug in a OBD2 reader to see if there are any stored codes? Also, is the car tuned for the 24lb injectors?

I don't know much about your swap but I'm trying to start small and work from there. I would guess since your not running COP's it could be a coil or wire is bad. If it is noticeable at idle, try pulling wires to see if the misfire gets worse, if it doesn't then there is the problem cylinder obviously.

Good Luck!

 

[wmburns]

How's the fuel pressure? Is the intake vacuum reference line connected and leak free?

 

[1987stangman]

How's the fuel pressure? Is the intake vacuum reference line connected and leak free?

Yes, I should have added that in my post. FP at idle is 32 and with the regulator vac line disconnected its 40. All the vac lines are new and I checked them twice.

joshjwc9:

I used my SCT tuner and my OBD2 scanner to check for stored codes and nothing.

Disconnecting plug wires on each cyl creates a miss in each one.

This why this is frustrating.

 

[wmburns]

Have the alternator tested for correct output and excessive AC ripple. A bad alternator diode will interfer with the cam sensor signal. This will cause the PCM to fire on every stroke. Excessive fuel could be an expected result along with misfires.

Are the battery terminals clean, tight, and corrosion free? Does the battery hold a charge?

Monitor EGR flow. Excessive EGR flow can cause poor running. IMO, this is likely in your case.

How many miles? What is the condition of the fuel injectrors? Consider an injector cleaning and flow test service such as injectorrx.com. Once cleaned and flow tested, the injectors are as good as new.

Monitor LTFT bank 1 and 2 at idle and under load. I'm interesting in seeing if there is a change from idle to load.

 

[1987stangman]

Have the alternator tested for correct output and excessive AC ripple. A bad alternator diode will interfer with the cam sensor signal. This will cause the PCM to fire on every stroke. Excessive fuel could be an expected result along with misfires.

Are the battery terminals clean, tight, and corrosion free? Does the battery hold a charge?

Monitor EGR flow. Excessive EGR flow can cause poor running. IMO, this is likely in your case.

How many miles? What is the condition of the fuel injectrors? Consider an injector cleaning and flow test service such as injectorrx.com. Once cleaned and flow tested, the injectors are as good as new.

Monitor LTFT bank 1 and 2 at idle and under load. I'm interesting in seeing if there is a change from idle to load.

Engine had 67k on when it went in place of the NPI. Battery is about a year old but has new terminal connectors and everything is clean and tight. The battery does hold a charge, however, the alt is as old as the car is. I did check the output using a DVOM on the battery at idle and it's around 13.99 to 14v. Its easy enough to pull off so I will do that when I get off work later.

Injectors are brand new, so is the fuel filter. I changed that last year when the rubber grommet on the gas tank started leaking.

As far as monitoring goes. Can I use SCT's live link to do this? I

 

[wmburns]

FWIIW, Excessive AC ripple will not show up on a multi-meter set the DC. It may show up on the AC scale. However, different meters will measure an odd AC waveform differently. It mainly depends upon how good your meter is.

The SCT live link is a great way to data log. You should be able to download to a spread sheet and create graphs if so inclined.

 

[1987stangman]

FWIIW, Excessive AC ripple will not show up on a multi-meter set the DC. It may show up on the AC scale. However, different meters will measure an odd AC waveform differently. It mainly depends upon how good your meter is.

The SCT live link is a great way to data log. You should be able to download to a spread sheet and create graphs if so inclined.

It's a pretty good meter. I use it when I'm diagnosing a/c systems on the property I work on. I will try using the A/C scale for fun.

I played with the live link software a couple times. There is a ton of stuff you can monitor and I was not real sure what to specifically monitor.

On the bright side on this. My Fox has had a chance to get out of the garage for the first time over a month.

 

[1987stangman]

Just to update. I pulled off the alt and had it tested and tested good. I also OHMed out the coil packs and they checked out good. If it doesnt rain tomorrow afternoon I will hook the PCM up to live link and see if I can get any ideas because at this point I'm stumped.

 

[flstang65]

Just because you aren't throwing a code or have a stored code, doesn't mean that you still don't have a misfire. Better scanners can check for misfires specifically. I still would have checked everything else that was suggested though. That's my .02. Let us know what you find.

 

[1987stangman]

Fixed it!

I fixed it fianlly. Cyl#4 had a bad injector.

Runs perfect now.

I just want to thank everyone who took the time to help me out. Just goes to show that even new parts that anyone could have shruged off a new part as good could be bad.