got new 306 running, but it feels like a dog. I can't seem to accelerate above 2k rpms. I have an aftermarket tachometer. Fuel system is sufficient, wally 255 and I'm sure I'm not making more than 260-280 whp. It seems to bog when I hit 2k rpms. Is this a ignition system issue? Thats the only thing I didn't really upgrade. Stock ignition, stock 8mm wires.
New 306 Doesnt Run Right, No Acceleration, Bogs
- Thread starter outdorsman
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OneWheelPeel
Active Member
Im not an expert but first Id check the timing. then check fuel pressure. Then I would inspect my plugs, distributor, and rotor. If the car was bucking and jumpy id test the tfi module on the distributor. I would also check my vacuum lines. If none of those were the issue I would then post on here too haha 
Is there any smoke coming out the back or an oil burning smell? Is in backfiring when it bogs?
Is there any smoke coming out the back or an oil burning smell? Is in backfiring when it bogs?
mikestang63
SN Certified Technician
first thing to do is check for vacuum leaks, timing, fuel pressure and then run the codes. Did you adjust the valvetrain properly?
Please post a full list of you mods, EFI or carb, if EFI, then MAF make, size and calibration, fuel injector size or color, heads, intake, cam, etc.
It is difficult to troubleshoot when we don't know what you have or if you are the one who did the work.
It is difficult to troubleshoot when we don't know what you have or if you are the one who did the work.
302 stock rebuild, bored .030 to a 306
GT40 heads rebuilt with new parts, tfs spring kit, stock ports. All done by the machine shop
Trickflow stage 1 cam, installed dot to dot
stock 1.6 rockers
Hooker super comp equal length headers
Jegs O/R H-pipe
flowmasters dumped
Electric taurus fan with flexalite vsc
24 lb injectors with matching Pro-m 75mm maf
Gt 40 intake, tapped for iac, stock ports
65mm TB with spacer
Stock t-5 with parts store clutch
fuel pressure is at 40 psi constant, I checked it and verified it. Timing is at 14* right now. I did a light pull and it pulls fine after 3k rpm. It bogs once it hits 2500-3k rpm but then resumes normal operation.
GT40 heads rebuilt with new parts, tfs spring kit, stock ports. All done by the machine shop
Trickflow stage 1 cam, installed dot to dot
stock 1.6 rockers
Hooker super comp equal length headers
Jegs O/R H-pipe
flowmasters dumped
Electric taurus fan with flexalite vsc
24 lb injectors with matching Pro-m 75mm maf
Gt 40 intake, tapped for iac, stock ports
65mm TB with spacer
Stock t-5 with parts store clutch
fuel pressure is at 40 psi constant, I checked it and verified it. Timing is at 14* right now. I did a light pull and it pulls fine after 3k rpm. It bogs once it hits 2500-3k rpm but then resumes normal operation.
Did you do the work or buy it as it sits now?
Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.
Dumping the computer diagnostic codes on 86-95 Mustangs
Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.
Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.
Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.
Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.
If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.
What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems
Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10
Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.
Or for a nicer scanner see Equus Digital Ford Code Reader (3145) Equus - Digital Ford Code Reader 3145.
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.
Dumping the computer diagnostic codes on 86-95 Mustangs
Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.
Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.
Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.
Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.
If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.
What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems
Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10
Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.
Or for a nicer scanner see Equus Digital Ford Code Reader (3145) Equus - Digital Ford Code Reader 3145.
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
I put my other 65mm tb on it with a new tps on the request of a poster on another forum and sure enough, i was able to make a clean pull from 2-4 with no bogs or sputtering. However my car does die in neutral or when I hit the clutch and let the rpms drop. I believe i need to adjust my idle?
I'll go through this first and then report.
Help me create the "Surging Idle Checklist" | Mustang Forums at StangNet
I'll go through this first and then report.
Help me create the "Surging Idle Checklist" | Mustang Forums at StangNet
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You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. 
It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 159,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 159,000 hits, which indicates it does help fix idle problems quickly and inexpensively.
