engine pulsing

[scotts93sho]

The first time it was a fluke, the second interesting and now the forth is worrying. The symptom is the engine pulses/revs on its own. The first time I was trying to accelerate up a small hill and I had very little power to make it up the hill. The car felt like a bucking horse. I was able to coast into the nearest parking lot and by the time I stopped and popped the hood, the car was fine. The check engine light was now off. This was about one month ago. Tonight on the way home from work, It did it again. This time was I sitting in traffic and the engine began to pulse from 1000 rpm to about 800 rpm. The engine light again came on. I killed the AC and it did not affect anything. I was not even in gear, only the brake may have been on and the radio. This lasted for about 10-12 seconds and then it all cleared up. The car ran fine for the rest of the trip. Any ideas as where to look? Years ago I remember having the same type of problem that was eventually diagnosed to be a throttle body problem (i think). How long would this error code stay with me? Do I need to catch it when it happen and not turn off the car to get an accurate code? Any help is much appreciated.

Scott

 

[92ShoOff]

I had the SAME problem happen to me several times man. I have NO idea what causes it to buck like that. The one thing that I found that kinda helped clear it up while it was happening was I put the clutch in took it out of 5th gear and shifted into neutral and revved the sh*t out of it a few times, put it into 4th (by the time I was done revving it in neutral it had slowed down a little) and it sputtered once then cleared right up. And it does this fairly seldomly.. never within the same week of driving it. I'll just be steadily crusing in 5th gear (I believe it's happened in 4th too, while trying to get up to speed to put it in 5th) and the thing will start bucking VERY HARD. CE light comes, the as soon as it stops it goes right off and it seems the problem doesn't stay in the computer's continuous memory or anything because I've never pulled anything up after I've made it home.

So if anyone knows what the heck is causing this PLEASE help us out! Thanks a bunch guys!

 

[CheckerSHO]

I had the SAME problem happen to me several times man. I have NO idea what causes it to buck like that. The one thing that I found that kinda helped clear it up while it was happening was I put the clutch in took it out of 5th gear and shifted into neutral and revved the sh*t out of it a few times, put it into 4th (by the time I was done revving it in neutral it had slowed down a little) and it sputtered once then cleared right up. And it does this fairly seldomly.. never withing the same week of driving it. I'll just be steadily crusing in 5th gear (I believe it's happened in 4th too, while trying to get up to speed to put it in 5th) and the thing will start bucking VERY HARD. CE light comes, the as soon as it stops it goes right off and it seems the problem doesn't stay in the computer's continuous memory or anything because I've never pulled anything up after I've made it home.

So if anyone knows what the heck is causing this PLEASE help us out! Thanks a bunch guys!

That sounds like an ignition misfire...sometimes a bad ignition wire will only show itself when under load in a high gear, then it will start bucking. A misfire will not set a code on our cars, as there is no misfire monitor like on 96+ cars.

 

[masho95]

Check your codes. If the CE light was on then there is a code in stored memory. Find out what it is.

 

[scotts93sho]

It did it again tonight. I am going to check the codes and see it anything is stored in memory. Absolutely no power when the engine in pulsing.

 

[masho95]

It did it again tonight. I am going to check the codes and see it anything is stored in memory. Absolutely no power when the engine in pulsing.

Sounds like a plan. I must have missed the end of your first post. No you don't need to keep the car running after the code first comes up. Once it's stored in memory you can pull it up anytime while reading the codes until it's erased.

 

[scotts93sho]

update of pulsing and 556 code

Well ,it gave me 556 (fuel pump relay primary circuit fault) and some old codes of 116 (ECT). So I cleared the old codes and then got 556 on start up and 411(idle speed not controlled properly generally too high) and 538 (failed on goose). I also can not hear the fule pump prime unless it is so quite that I can not hear it. As I remember you should be able to hear it. If the fuel pump is dying, will the car run without the pump working? THis may sound like a dumb question but can the engine suck the fuel it needs without the pump? This is my third stock ford pump in the last 6 years. If I need a new one, what should I buy?

 

[92ShoOff]

Scott.. in answer to your question about the fuel pump.. no, the car will not run if the fuel pump dies out on you. I've had a fuel pump die on me before and all the engine will do is crank over after you use the last drops of gas left in the line after the pump stops working. When I first got my SHO last October I ended up replacing my fuel pump thinking it was causing the bucking problem. I believe at the time I had also gotten a 547 code (fuel pump secondary circuit failure). I replaced my old pump with a Walbro 190lb. fuel pump and thought that cleared the problem... but several 7 months later my car is still acting up. Just yesterday when I ran a scan on the car I did get the 547 code again... but I've been told before to ignore that code. I don't see why it should even come up... it's a new fuel pump, and the car has bucked several times prior to getting this code again last night.. and this is only the 2nd time I've gotten this code on memory.

I also did get code 157 last night (MAF circuit below minimum voltage). I had gotten this code once before and it didn't go away for a while. I had the completely stock airbox setup with a paper filter the last time I got this code some months back, so in hopes to correct the problem I ordered a whole new PRO-M 80mm MAF meter with a conical filter which was tuned for my car. Well the code went away before I got to bolt on my new setup.. but I still bolted it on afterwards and the new meter has been on since. Now I'm getting the darn code again! Anyway.. if I were you, Scott, I would go with a Walbro 190lb pump (beats the weak factory pump) or you can give the BBK 190lb pump a shot also. Just open a Summit Racing book and turn to the page for the 5.0/4.6 Mustangs. You can use the BBK pump they have in there... same exact pump as the Walbro. So anywhere you find a BBK pump for a Mustang around that year wpuld be perfect.