Mustang efi stumble and backfire

[landshark99]

I have been having an intermittent issue where the 76 will stumble then lack power and sometimes backfire through the exhaust. Happens allot when pulling away from a stop or slow rolling coast then giving throttle. Letting off and hitting the gas again sometimes "cures" it but seems to be getting worse. I check the timing last night and it was at 13 I took the timing back to 10 and doesn't seem any better.

I have been looking at posts here in CB.com and my next thought was to check vacuum then check and clean the MAF And TPS.

I saw one post where it was a bad distributer but wanted to trouble shoot before I start guessing at replacement parts.

Any other advice?

 

[Viperwolf1]

Check fuel pressure.

 

[landshark99]

Guess I could run a softline up through the driver air vent. Will see what I piece together

 

[landshark99]

I have steady 38 psi on idle and throttling it up when parked. 40psi when I shut off.

I have a steady 14hg of vacuum at idle about 17-19 with some throttle. Blipping the throttle it goes up to 20 or so.

I will see if I can put some kind of line together and make the fuel pressure gauge readable while driving.

 

[landshark99]

Put a electronic auto meter fuel pressure gauge on the rail. Getting 32-34 psi at idle. Romping the throttle will spike it to 38 or so. Light throttle cruising it hovers around 32 but drop a bit more coasting.

Seems low to me should be 38 pretty much all the time of not higher?

My next step is to check the voltage at the pump.

After that I assume drop the tank?

 

[Rox Crusher]

Since its holding 40 PSI after shutting it off, that pretty well rules out the fuel pressure regulator or a leaking injector.

I would agree that if you don't find a voltage problem, it's probably a clogged / clogging filter sock on the pump. Or maybe the hose between the pump and the pick up tube has a problem.

 

[landshark99]

I'm going to pull the tank this week

 

[CH3NO2jim]

MAP sensor

Sounds like a bad MAP sensor to me.

 

[KyleQ]

Run the codes and see what it does - mine was doing that and I had 12v going to the coolant temp instead of 5v and after that I had no issues.

 

[67EB_in_619]

Cleaned the air filter lately (k&n?) .. sounds like the issues you can have with a dirty MAF (after cleaning the k&not, the oil gets on the MAF element)... buy some MAF cleaner (don't use anything else) clean it up and give it a try.

 

[landshark99]

I had planned on cleaning the maf again here tonight or tomorrow. cleaned it not too long ago but bronco sits quite a bit - month or two at a time. Have less than 5K on it since frame off.

Ordered a quieter pump as I never liked the whine of the in tank pump anyway and will wrap it in fuel cell foam as well.

 

[landshark99]

Cleaned the MAF, act and throttle body. Will see if it makes any difference but I still plan on dropping the tank.

Everything was really clean but you never know.

 

[Rox Crusher]

Silence isn't golden........

 

[landshark99]

I was giving it a few days.

Might jinx it but stumble is gone so far after I cleaned the MAF, ACT and throttle body. Didn't look dirty but guess it was.

Not running an K&N so no oil in my filter.

 

[WheelHorse]

TPS below .98?