Fox Drivability issues

Maciasmarci

Member
May 19, 2021
40
1
8
26
Stockton
I have a rebuilt 306/t5 w/ used b-cam gt40 heads /upper lower intake ,19lbs injectors cold air intake, 39psi pressure timing is at 10 degrees . Replaced fuel pump , injectors, spark plugs , tfi module , iac, tps, checked resistance on wires, no vac leaks, tried adjusting tps and iac. Adjusted idle screw all the way in to keep the car from dying . Car idles at 800-900. Idles fine . Only when I drive around in the streets and try to switch gears is when it stalls on me. As soon as I press the clutch and switch to neutral the car stalls . Another issue is that when I punch the gas from a complete stop ,at WOT it does not respond immediately. It will slowly pickup speed and power. Codes are 34,44,94. I should say it doesn’t have the thermactor holes these heads so the air pump/ solenoids are inoperable. Any ideas
 
  • Sponsors(?)


General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
22,758
8,255
203
polk county florida
I would check timing and vacuum, checking with the spout plugged in to make sure computer is advancing the timing, remove spout bump timing to 12-14*, clear the computer. Test drive, I like to do some stop and go, then a few minutes of non stop at highway speeds. Check for codes.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
38,665
14,576
224
Massachusetts
If you are cranking in the idle stop screw, you are probably messing with the range of the IAC. You really need to adjust that screw with the IAC disconnected.

Pull the plug for the IAC and adjust the idle stop screw to where you want your idle to be set at. Try for 750-800RPM which will be a bit on the low side, but you want the IAC to then slightly open to regulate the idle. After adjustment, shut engine, plug IAC back in and disconnect the battery for 20 mins or so to reset the ECU. Start the engine back up and give that a shot and see if it will maintain idle.

Ensure the IAC is clean and freemoving. If it's gunked up at all it may be slow and unable to react in time.
 
  • Like
Reactions: 1 user

Maciasmarci

Member
May 19, 2021
40
1
8
26
Stockton
I would check timing and vacuum, checking with the spout plugged in to make sure computer is advancing the timing, remove spout bump timing to 12-14*, clear the computer. Test drive, I like to do some stop and go, then a few minutes of non stop at highway speeds. Check for codes.
I’ve tried the timing but will try checking vacuum.
 

Maciasmarci

Member
May 19, 2021
40
1
8
26
Stockton
If you are cranking in the idle stop screw, you are probably messing with the range of the IAC. You really need to adjust that screw with the IAC disconnected.

Pull the plug for the IAC and adjust the idle stop screw to where you want your idle to be set at. Try for 750-800RPM which will be a bit on the low side, but you want the IAC to then slightly open to regulate the idle. After adjustment, shut engine, plug IAC back in and disconnect the battery for 20 mins or so to reset the ECU. Start the engine back up and give that a shot and see if it will maintain idle.

Ensure the IAC is clean and freemoving. If it's gunked up at all it may be slow and unable to react in time.
I meant to mention that as well . I tried adjusting with the iac disconnected and it would barely idle on its own unless I turn the screw all the way I
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
38,665
14,576
224
Massachusetts
Even with the screw all the way in, your idle is pretty low. Should be able to get 1500RPM or so with it all the way in.

Have you checked for vacuum leaks?
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
38,665
14,576
224
Massachusetts
Did this combo ever run correctly or is this the first time setting it up?

What concerns me here is that with the idle screw in all the way, you can only get it to 800-900 RPM. Like said, on similar combos that should result in a 1500 RPM idle easily.

Those codes won't really affect much here. Were those codes run with the engine off? Or with the Engine running? I would suspect that you should have gotten a code 12 as well (Idle too low) since you can't get the idle much higher. If those were the engine off codes, please proceed and start the engine and run the engine running codes.

Do you suspect you are running rich at all? Does the engine stumble a bit as if it's loaded up with fuel and then clears a second later and revs? When the engine stalls out, does it easily restart or does it stumble, like it's flooded out? Sometimes running overly rich can cause the car to easily stall out. If it stalls and doesn't easily start, does depressing the gas to the floor (flood clear mode) make it restart easier?

Was the cam degreed when installed?

Does it sound at all like it has a misfire? Are you able to run the cylinder balance test procedure at the end of the code-reading process? Sometimes it won't let you if it's unable to maintain idle control. How did the plugs look when you replaced them? Did any look fouled? Were they all showing signs of even burning?

Have you run compression to see if a valve or two is being left hanging open?
 
  • Useful
  • Like
Reactions: 1 users

Maciasmarci

Member
May 19, 2021
40
1
8
26
Stockton
No this issue was ongoing prior to the motor rebuild. It does seem like there’s a misfire though because it always had an unusual engine shake. Tfi was changed 2 times and ignition coil. Plug cables are from Amazon don’t know what brand but spark plug gap is at .50. My codes were done while engine was running and also engine off ignition on. Similar codes popped up on engine running. I can check again today. I had a wideband sensor on both banks and it would read 14-15 on the gauge. While cruising guage stays at about 12 -13 ish. Compression test was made and checked out ok by my mechanic
 

Maciasmarci

Member
May 19, 2021
40
1
8
26
Stockton
No this issue was ongoing prior to the motor rebuild. It does seem like there’s a misfire though because it always had an unusual engine shake. Tfi was changed 2 times and ignition coil. Plug cables are from Amazon don’t know what brand but spark plug gap is at .50. My codes were done while engine was running and also engine off ignition on. Similar codes popped up on engine running. I can check again today. I had a wideband sensor on both banks and it would read 14-15 on the gauge. While cruising guage stays at about 12 -13 ish. Compression test was made and checked out ok by my mechanic
I’m not sure if the cam was degreed by the engine rebuild techs.
 

Maciasmarci

Member
May 19, 2021
40
1
8
26
Stockton
20C3F4B9-46CD-46EB-A109-0B482D514C01.jpeg
Did this combo ever run correctly or is this the first time setting it up?

What concerns me here is that with the idle screw in all the way, you can only get it to 800-900 RPM. Like said, on similar combos that should result in a 1500 RPM idle easily.

Those codes won't really affect much here. Were those codes run with the engine off? Or with the Engine running? I would suspect that you should have gotten a code 12 as well (Idle too low) since you can't get the idle much higher. If those were the engine off codes, please proceed and start the engine and run the engine running codes.

Do you suspect you are running rich at all? Does the engine stumble a bit as if it's loaded up with fuel and then clears a second later and revs? When the engine stalls out, does it easily restart or does it stumble, like it's flooded out? Sometimes running overly rich can cause the car to easily stall out. If it stalls and doesn't easily start, does depressing the gas to the floor (flood clear mode) make it restart easier?

Was the cam degreed when installed?

Does it sound at all like it has a misfire? Are you able to run the cylinder balance test procedure at the end of the code-reading process? Sometimes it won't let you if it's unable to maintain idle control. How did the plugs look when you replaced them? Did any look fouled? Were they all showing signs of even burning?

Have you run compression to see if a valve or two is being left hanging open?
1F958B01-E277-4EFA-B389-033EBF939281.jpeg
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
38,665
14,576
224
Massachusetts
It does seem like there’s a misfire though because it always had an unusual engine shake.

I think I would focus in on this. Is the harmonic balancer new? Have you checked to see if the balancer has slipped? Does the rubber isolator in the balancer look cracked or squeezing out at all? If the balancer has slipped, the incorrect timing could make it run the way it is.

That plug looks a little fouled. How many miles are on that? Do all 8 look the same?
 
  • Useful
  • Like
Reactions: 1 users

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
38,665
14,576
224
Massachusetts
It's not the clearest photo, but those plugs look rather dark for having only 100 miles on it.
 
  • Agree
  • Like
Reactions: 2 users