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6Bucs, Ford Senior Master
Category: Ford
Satisfied Customers: 872
Experience:  Ford senior master tech, 18 years experience.
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I am trouble shooting a hesitation upon acceleration on a

Customer Question

I am trouble shooting a hesitation upon acceleration on a 4.6L, 95 Ford Thunderbird LX. The symptom includes intermitten back fires, bogging out, no acceleration or slow acceleration as if restricted in gas. I introduce a secondary source of fuel (carb cleaner) while accelerating and it seemed to react to it. In other words it accelerated fine. I checked several components including mass air, vacuum leaks, coils, crank sensor, cam sensors, codes, tps egr and spark plugs, vacuum, calatlytic converters and all checks out. The problem is consistent while it is cold or hot, but I did notice that upon start up the acceleration is normal for about the first two accelerations. After it just gets worse. the can does not shut off but does get a bit shaky. I also noticed that if i turn the ignition switch off and on the acceleration is normal for the first couple accelerations and back to bogging out. Everytime I close the switch and open it, the acceleration returns and goes away. Any suggestions or questions on a solution for this strange symptom?
Submitted: 1 year ago.
Category: Ford
Expert:  6Bucs replied 1 year ago.

Hello and thank you for your question. My name is James.

Given the symptom and behavior of the vehicle, have you had a chance to check the fuel pressure yet? Low pressure will cause what you describe. You'll want to see 33 psi minimum. We can chat back and forth here until we get to the bottom of it.


Customer: replied 1 year ago.
Excuse the delay, there was a problem with the response system due to internal mix up. Yes, the fuel pressure checked, with additional 10psi resoponse from Fuel Pressure Regulator when vacuum removed. That was one of my thoughts as well. Psi would also spike upon acceleration. It would never go passed 45psi. I also removed vacuum from regulator to increase pressure but the symptom was still present.
Customer: replied 1 year ago.
I kept an eye on the short term fuel trims while attempting to reproduce the symptom. They showed a good air/fuel mixture of 1% to 2%. While accelerating gradually the trims did begin to compensate for a "lean condition" of about 19%, but when the symptom began the trims went to -9% on both banks and stood there until symptom went away once I released accelerator. At times it would just continue throughout an extended time period or until ignition was cycled.
Another theory of mines led me to determine if an alternator interference was present, so I removed the belt and disconnected regulator and power cable, But still with same Symptom.
Expert:  6Bucs replied 1 year ago.

Ok thank you. Can you tell me what mass air flow sensor readings you found?

Can you also look at the BARO reading and let me know what it is?

Customer: replied 1 year ago.
MAF: .79v idle and up to 4.v wot no drop outs.
BARO: 157.6Remember, with engine running with symptom present, If I cycle ignition from off to on, symptoms are no longer present for the following 3-5 seconds.
Customer: replied 1 year ago.
I also disconnected battery to clear any memorized compensating conditions. Another, way I eliminated the possibility of MAF failure, was by turning ignition off and disconnecting MAF, starting engine and seeing if symptom was still present but all remained the same with the same symptom.
Expert:  6Bucs replied 1 year ago.

Okay thank you. The Baro reading indicates a geographic elevation of about 4600 feet above sea level. Does this sound correct for your location?

Customer: replied 1 year ago.
That is off by about 4500, 6Bucs, Where did you get those specs from? The elevation of the vehicle is about 72' above sea level. Which would put 157.6Hz at proper Baro pressure-(Read more at:
Customer: replied 1 year ago.
Can there be some internal (vacuum) leak causing these lean like conditions? Ever heard of any such things? I asked the owner if he had done any work on his car prior to present symptom and he said that he had his transmission changed out 7 days before. I don't see any connection there but thought I should mention it. Awaiting your response.
Customer: replied 1 year ago.
Hello and thank you for your question. My name is ***** ***** . We can chat back and forth here until we get to the bottom of it."Hey James I am not sure what happened but I never received a response after the last message I posted. Did you opt out?