EFI experts; problem studdering acceleration... makes me wanna go carb

[Boss 351]

Hi guys!

My car will, on occasion, studder on acceleration from 1000 to 3100rpm. Above that it will studder less. This will happen when the engine bay gets hot and sometimes only when it's warm. My temp gauge reads between 1/8 and 1/4 depending on traffic.

It runs as if it's missing spark so I replaced the TFI module (on the dizzy) the car runs a little better but will still studder. Then I thought maybe it's the coil so I put in an Accel supercoil but it started to studder just the same (I admit it only did this after 25 minutes of driving in real hot conditions, normally it would do the problem after only a few minutes). The new coil was burning hot when I removed it (returned it to the store and put my old one back on).

I have problems with my IAC and TPS sensors since my engine will sometimes surge at idle and often it will stick at 2500 rpm (I quickly turn the engine off adn on to "unstick" it). I tried to connect my scantool but it keeps telling me I have a connection problem I don't have a CEL either. If I revv the engine with the clutch pushed in, it doesn't show any signs of missing spark but on idle I will hear a certain little "poof" as if one of the cylinders isn't firing.

I'm not sure what it could be, my spark plug wires (Ford Racing) and spark plugs (Stock Fords) are not old at all except for my coil wire which is God knows how old. I may get a new complete set of wires or just try and find a new coil wire to test that thing out. Also my TB was full of green and white crap, it was the gasket between the TB and EGR spacer that leaked coolant into the intake. I fixed that but I still have the problems.

Right now I'm real close to getting a performer RPM airgap intake, a double pumper 650cfm carb, Holley inline electric fuel pump, MSD dizzy, etc... to swap over to carb'd.

 

[vristang]

Bump.

After reading this I suggest starting with finding out why the code reader won't work. There is little chance of diagnosing your problem without pulling the codes.

I am not sure how to trouble shoot the code reading connectors, but jrichker will be able to


jason

 

[jrichker]

With the power off, measure the resistance between the computer
test ground (black/white wire) on the self test connector and battery
ground. You should see less than 1.5 ohms.

If that checks good, remove the passenger side kick panel and
disconnect the computer connector. There is a 10 MM bolt that holds
it in place. Measure the resistance between the STI computer self
test connector (red/white wire) and pin 48 on the computer main
connector.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine

The following is a view from the computer side of the computer connector.

 

[1fastsn95]

I had a similar problem on my 88 GT. Turned out to be a bad TPS. Replaced it, ran like new. Good luck

 

[795.0pacecar]

I had a similar problem with my car and I found out it was the red key on ignition wire that goes to the computer. It turns out that wire powers quite a few of the sensors. This probably isn't the solution to your problem though, Im just throwing it out there as a possibility. My wire came lose because I wired my car up to have fuel injection and my connection wasn't great so it came lose.

I've also heard of bad ACT and ECT sensors causing similar problems.

 

[Boss 351]

Thanks guys, I will check to see why my code reader won't work following the posted advice...

Now an update: I figure I wasn't looking at the right place and that there wasn't fuel. So I changed my fuel filter and what I saw wasn't nice. When I unplugged the old filter, dark brown gas flowed out of it. The filter was dead, torn element and even parts of element was coming out. So I put a new filter in, after making sure the gas in the tank wasn't brown and put in a can of injector cleaner.

Car runs a little smoother but will still on occasion studder like before (although more rare now). I may have to perform a full fuel system clean up.

 

[gt90stang]

A remote possibility is that the engine can get into a load condition that causes the HEGOs to report wrong information to the PCM. This causes bucking and or popping on mild to medium acceleration. I corrected this by lowering the open loop load limit vs ECT function in the PCM. This allows the PCM to go into open loop at a lower load that the stock setting of 0.77, mine is set to 0.45.

Good Luck, Don

 

[Daggar]

The HEGOs are taken out of the loop at WOT.

One other thing you may want to look into is either a vac leak or a vac/boost gauge that allows a regulated release. In other words... if you run a gauge like this, temporarily remove it from the vac system and plug it. If it cures your problem then reconnect it with an inline orifice. .050 should do for starters.