Why does my car jump and buck and have no power?

MACDADDYMOTORSPORTS72

MEMBER
1993 FORD MUSTANG
25,000 MILES

I have a 1993 5.0 mustang. It is hard to crank and when it does it has a rough idle almost like it has a bigger cam. It bucks on the road and has no power at all. I got it from my brother and he replaced the fuel pump, fuel filter, distributor cap and rotor button plug wires, plugs, he said that he took the pickup assembly out and cleaned it and also took the mass air flow out and cleaned it with a electrical spray cleaner, and the computer was rebuilt because he had ants in it. [? ] I found that the firing order was wrong against what I had so now it is [ 1 3 7 2 6 5 4 8 ]. It didn't help much. I also found out that he has been adjusting the timing by turning the distributor so I got the light and tried to set it back at 14 degrees, what I was told I have no book yet. The mark was jumping around and I could not get a good reading. I was also told that there is a plug that needs to be unplugged at the distributor to be able to set the timing but all I see is the control module plug. Before the fuel pump went bad the car ran fine and was pretty strong considering the mileage. What do you think I need to do or check next?

5 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Did you check the engine compression?
Is the MIL indicating and did you check for troube codes?

Ignition timing
1. Turn all accessories off. Set parking brake, and block wheels. Connect timing light to engine. Disconnect single in-line Spark Output (SPOUT) connector (Yellow/Light Green wire) near Ignition Control Module (ICM) at distributor.

2. Start engine and warm to normal operating temperature. Place transmission in Park (A/T) or Neutral (M/T). With engine at idle RPM, check ignition timing. Turn engine off. Reconnect in-line SPOUT connector. Check computed ignition timing. Computed ignition timing should be advanced beyond base timing.

BASE IGNITION TIMING

Degrees BTDC @ 10 @ 575-725 RPM

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Monday, September 17th, 2012 AT 4:39 AM

MACDADDYMOTORSPORTS72

MEMBER
3 POSTS

Thanks for the reply. I checked firing order and it is correct. I found the plug at the distributor and checked the timing and corrected the timing as best I could since it will not idle smoothly but still it is pretty close. After asking my brother more about the car and what he did to it I found out that he had also cleaned the mas air flow with spray brake cleaner and that replaced plugs, not wires, cap and rotor button. I checked and it is getting good fuel at the bleeder valve, but I don't have a pressure gauge so I can only say this. It has compression. When at idle it lopes and idles very low but as soon as you tap the gas it picks up smoothes out for a second and does the same lope and low idle. I can hold it at about 1200-1500 rpm and it sounds like a spitback noise from a carbed motor but not as loud and definite. My brother also said that this is one reason that he stopped driving it and let it set for about a year then that is when ants got in the computer. Could it be fuel injectors and is there a way to check because they are not cheap? What can we check now?

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Monday, September 17th, 2012 AT 11:48 PM

KHLOW2008

MECHANIC
41,814 POSTS

Symptoms indicates the idling speed is not stable. Check the throttle bore and if it is dirty, give it some cleaning with carb cleaner. Have the IAC cleaned as well.

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Tuesday, September 18th, 2012 AT 8:03 AM

MACDADDYMOTORSPORTS72

MEMBER
3 POSTS

I cleaned throttle bore and the IAC it seemed to pep up a little but the idle is still off and if I hold it at about 2000rpm it will speed up and slow down. I drove it up the road and it has picked up some but it still bucks and jerks like it is giving out of gas. It makes like a thud sound and then it picks up, thud sound, picks up. I mean it nose dives. Any more ideas? PLEASE

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Wednesday, September 19th, 2012 AT 12:09 AM

KHLOW2008

MECHANIC
41,814 POSTS

Get a DVOM and ohm out the plug wires. None should be infinity or anything above 20k ohms. You mentioned that you have compression but did you test the readings?

Anyway the symptom description indicates it is more likely to be ignition related rather than engine mechanical.