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1989 mustang running rough and loss of power

2031 Views 9 Replies 3 Participants Last post by  87frankenstang
ok so i have been working on this for a couple of days now and i think i need some help. so i found that when it is idling it runs fine but when i put it in gear it and give it a decent amount of gas(not full throttle) the car slows down but when i give it full throttle it gives it enough gas to accelerate but no where near as fast as this mustang normally accelerates. so i looked at plugs, wires, cap, and rooter and not knowing how long ago they have been changed out(i bought this car a year ago used) i replaced that and it help out a little bit but still ran really rough. changed the fuel filter and then it ran great again but only lasted for about 2 days before all the problems came back. replaced the fuel filter again to find the new one i just put in was clogged up again but unfortunately this did not fix the problem. tested the fuel pressure yesterday and found it idled at 35 psi and ran at 40 psi and i think the number are good.? i rechecked the firing order and all the parts i just replaced to make sure there was no where and everything check out good. ran the check engine codes yesterday and it told me that there is a problem with the mass air flow sensor, and the oxygen senors. don't really know what to do about the oxygen sensors yet but i did clean the mass air flow sensor and cleared the code but it just came right back. im up to any suggestions on what to do next i have ordered a new mass air flow sensor to hopefully fix it.
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You said a NEW fuel filter was clogged within 2 days?

Well the only place that crud came from in the tank, so think about. That means the fuel pump had to pass that crud through it. Maybe the fuel pump is going out now? There is also a filter screen on the pump itself inside the tank maybe the larger partcles are now clogging that up.

When I bought my Mustang the fuel pump died randomly when I was driving...that turned into me replacing the entire tank along with the pump due to rust...That tank was about 100$ from advance, they literally had one on the self right there. So prepare yourself for that if you decide to go into the tank...expect to need to replace it, especially if you clogged a new filter. That would be rust, or your getting gasoline with dirt in it or someone is putting dirt in your tank. The most likely one is rust from the tank...

Measure your fuel pressure again except this time look at the guage you use, and have someone else quickly give the car WOT, like mash the gas and quickly let off. The fuel pressure shouldn't plummet when this is done, small fluctuations are fine but there shouldnt be a huge drop. If there is your engine is fuel starved and its time to replace that pump and in all likelyhood the tank too.
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Didnt see your sentence about the bad MAF sensor. If your check engine light is on, and the code is for a bad MAF sensor then thats a huge part of your power problem..No/bad MAF means poor running and no power
I'm also gonna say maybe the fuel tank I just had to replace mine do to rust as well and either way clogging a filter in two days I say drop the tank and take a look.
ok thanks for the suggestions here is an update for what has gone on so far I have replaced the Mass Air Flow sensor with a new one with no change in state it still runs really rough. one thing I did notice is after I drove it is I went to check the oil just to make sure it still had some in it and noticed after I took out the dipstick out of the tube came white smoke. I am thinking next thing I will do is to change out the O2 sensors because I have an error code on that as well and hope that helps. also how hard is it to drop the tank to see its condition or is there something I can put in it to see what it looks like inside?
also one thing I forgot to mention while checking the check engine lights it did give me a code for the EGR valve being closed. im wondering which one might be a more promising fix the O2 sensors or the EGR valve or is the problem a combination of the 2.
And egr valve that is stuck open will make your car run rough as hell and pretty much like how describe. Worth looking into...
looked at the EGR valve and all looked good then reset the computer and drove it around some and it still is just as bad. I did another check engine light test an got code 12 and 91. I also ran a cylinder balance test ran it 3 times with varying results. the first time it told me just cylinder 5 was bad. the second time it said cylinder 5 and 6 and the third time it said 8,6,5,3, and 2 where bad. this seems odd to me but am now going to look at the timing to see if that is still good.
got a timing light and found the timing was off redid the timing and now it runs great. looks like the timing was just off.
"After the first cycle of the Cylinder Balance test the EEC-IV will then perfrom the Cylinder Balance test again. The test will continue to cycle at twice the threshold of the previous test until the engine is shut off. Each time the EEC-IV finishes a Cylinder Balance test cycle it will display codes to your reader. "

That is why your cylinder balance test seemed to get worse and worse as you did the test....each cycle is more critical then the last to determine the weakest cylinders in the engine... looks like cylinders 1,4 and 7 are the strongest...and cylinders 5 and 6 are the contributing the least amount of power in the engine.

That being said, glad you figured out the root issue.
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