Q: '72 Mach 1 with 351C. Runs, idles, revs in park. Sputters, chugs and coughs in Drive. Any suggestions?

asked by on

Engine idles and revs in Park with no problem. When under a load (in Drive) in sputters, coughs, chugs and backfires. Have rebuilt the carb and checked for vacuum leaks. Any suggestions to trouble shoot?

My car has 36000 miles.
My car has an automatic transmission.

Check for proper advance of ignition timing. In particular, verify that advance curve you observe matches factory spec. Measure fuel pump output/pressure against factory spec. If engine compression is good and balanced, apart from timing check and fuel pressure check, you have to diagnose the fuel (carburetor) and ignition systems and the fastest way to do that is put the engine on an automotive scope to look at secondary firing patterns in all cylinders. Even though you have rebuilt the carburetor, faults in the carburetor are still a very plausible cause. I remember as a teenager rebuilding a carburetor (66 Falcon) and the engine then ran just as you have described. I took it to a shop, they put it on a scope and told me to buy a new carburetor. Problem solved. If you desire a diagnostic, the service to request is poor operation/sputtering diagnostic. If you request that service, the responding certified mechanic will get this taken care of for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. '72 Mach 1 with 351C. Runs, idles, revs in park. Sputters, chugs and coughs in Drive. Any suggestions?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: How do I remove the key fob from the ignition switch?

Removing the key from the ignition switch is very easy. First, if your vehicle has an automatic transmission, make sure that it is in PARK. Then, turn your key fob counter-clockwise to the farthest setting, OFF. Then pull the key...

Q: Q: My car is rattling while accelerating

A stretched timing chain, worn timing chain tensioner, or timing chain guides can cause a rattle. It would be heard more at the front of the engine. Besides a visual inspection or using a mechanic's stethoscope to isolate the noise,...

Q: Oil pressure dropped and the engine is trying to stall but only when the transmission is in gear and at operating temperature.

Hi there. Check the oil pressure sensor on the engine. Look at the wiring harness to the sensor and see if harness is burned or loose. If the harness looks normal, then you would need to take a mechanical oil...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...