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Engine Stumbling at under load

N

Nathan

New CEG'er
Joined
May 9, 2003
Messages
10
Location
New Brunswick, Canada
My 2.5L engine is stumbling / bucking when I stomp on the pedal (at all RPMs, but mostly at lower RPMs). If I ease off the gas then it drives fine, but try to feed it too much and it dies. Recently put on new plugs & wire, fuel filter, and o2 sensor. No CELs. The car works best after cold start.

Am wondering if it could be fuel pump, MAF sensor, injectors... any suggestions?
 
Nathan said:
My 2.5L engine is stumbling / bucking when I stomp on the pedal (at all RPMs, but mostly at lower RPMs). If I ease off the gas then it drives fine, but try to feed it too much and it dies. Recently put on new plugs & wire, fuel filter, and o2 sensor. No CELs. The car works best after cold start.

Am wondering if it could be fuel pump, MAF sensor, injectors... any suggestions?
Click to expand...
Was it "stumbling" before you changed out the wires and plugs? If not, what wires and plugs did you use?. Stumbling or hesitation under load can be caused by bad wires, plugs, clogged fuel filter or fuel pump. Check for codes with a scanner anyway even though you indicate no CELs. Also, since you mentioned that the engine runs better cold, it is running richer at that time which could indicate a vacuum leak condition after the engine warms up and the computer leans out the mixture.
Karl
 
if he used Champion Spark plus that would be my assumption causing the bucking. try putting your old plugs and wires back in, that is assuming you didnt have an issue with the old plugs and wires.
 
98SVTC said:
Was it "stumbling" before you changed out the wires and plugs? If not, what wires and plugs did you use?. Stumbling or hesitation under load can be caused by bad wires, plugs, clogged fuel filter or fuel pump.....
Karl
Click to expand...
...and SP wiring order. Check that first.


SPwiring order. Note the 4-6-5 for the coil pack.

Firewall side
4- 6 -5 <--coil pack
3-2-1

1-2-3 <--engine
4-5-6
Radiator side


SP gap should be 0.054 inch.


Autozonelink. groundstrap coilpack
http://www.autozone.com/az/cds/en_us...rInfoPages.htm
 
I changed the wires and plugs about a year ago, as a result of a cracked boot. Car had been working fine until recently. Then, the stumbling was more related to the lack of power at low rpms, and would not be evident at higher rpms. Now, the car has power at all rpms, unless you push the gas down hard, then it starts to stumble and looses power.

P.S. I checked the codes a month ago and only one was for o2 sensor lean/rich. I changed sensor and it code hasn't come back. This bucking has been going on for several months now. o2 sensor didn't seem to fix a thing (other than CEL).

A side note: my car has always seemed to have more guts when cold. I don't think my wife would ever notice, though.
 
Nathan said:
A side note: my car has always seemed to have more guts when cold. I don't think my wife would ever notice, though.
Click to expand...

thats normal, as the duratec warms up the computer can pull timing pending upon how hot the outside temperature is and the engine coolant temperature.
 
That's how mine acts when I have carbon tracking. Had misfire, but not enough to set off a CEL. Look at plugs insulator (white porcelin part) for little "tic" marks that are black, and check inside the plug wire boots for a grey/white line running parallel to the boot. Make sure you use dielectric grease when installing new wires.

If you decide to clean off the MAF, use a cleaner designed especially for that.
 
So you guys think it is more related to spark than fuel delivery?

I was thinking fuel, as power loss occurs immediately after gas pedal is pressed and rpms don't seem to matter. Wouldn't I smell gass if there was a lack of spark?
 
I just cleaned the MAF and checked the plugs. The the front middle has got oil around it, and one is dry, and other seems to have a bit of oil on it. I took the middle one out and the oil was through the threads (although this could have happened as I unscrewed it). What does this mean? With the MAF off the car still was stumbling as i punched the throddle.
 
That means the gasket (seal) around the spark plug hole in the valve cover is leaking. Oil will ussually cause a misfire in that situation. You'll need to pull the valve cover, and install a new gasket around that hole. Actually, you will want to install all new gaskets on that vavle cover (they come as a set), so you won't have to do this again anytime soon.
 
Is your fuel filter installed correctly? It's a one way filter so if you've got it backwards, that could be your problem.

Check your vacuum lines too. Especially the long red one going to the fuel pressure regulator.

Might want to check the fuel pressure as well. Get a guage, hook it inline and test.
 
I had a set of new wires last me 5,000 miles on my Mystique.

My SVT recently ate a set of new Taylor wires at 3,000. The hesitation was so bad at low RPM's the car was barely driveable.

I'm now running a $6 set of used wires from a salvage yard and my hesitation (like yours) went completely away.

What can I say, my cars eat plug wires! Wires have always been the fix for me.
 
I'll throw in my vote for plugs and wires.

Best to replace the plugs and wires at the same time, since bad plugs will kill new wires, and bad wires will kill new plugs.

Your issue sounds EXACTLY like mine, when I needed plugs and wires. I replaced the fuel pump, MAF sensor, and fuel filter, because I was convinced the plugs and wires were good. I was wrong.

When my fuel pump actually DID fail, the symptoms manifested themselves when I turned a hard corner. When I hit the gas coming out of a corner, it bucked and missed.
 
I replaced the fuel filter a month ago as an attempt to fix the problem, no change. I'm sure it's on correctly.

I checked the wires (except the back right), rubber boots were fine, and they seemed ok. Might have 30k on the new wires. I also checked the resistance on the ignition coil and it was OK.

Wouldn't it be so much easier working on a truck, there is no room no these contours 2.5L engines!

Thanks for the input, maybe I should try new wires. I just hate to throw away the money without knowing if they are defective.
 
Andy Bennett said:
When my fuel pump actually DID fail, the symptoms manifested themselves when I turned a hard corner. When I hit the gas coming out of a corner, it bucked and missed.
Click to expand...

Thanks, Andy. That certainly rules out the fuel pump, and confirms what I have read elsewhere regarding fuel pump failure.

Did you have to take the wires off at the salvage yard? $5 seems pretty cheap!
 
I actually bought a super-el-cheapo set of wires off eBay for like $12 shipped, brand new. It fixed my problem, and has been fine for well over 2 years now.
 
Andy Bennett said:
I actually bought a super-el-cheapo set of wires off eBay for like $12 shipped, brand new. It fixed my problem, and has been fine for well over 2 years now.
Click to expand...

How old were the existing wires and did you see any damage on them after removal? When I replaced mine there was an obvious crack in the plastic boot and evidence that it was sparking. Mine current ones look like they did a year ago (new).

Also, where do you put the die-electric grease (in the boot, outside the boot, etc.)?
 
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I noticed damage on the plug porcelain; couldn't really see anything inside the plug wire boots; that was enough for me.

I put the dielectric grease inside the boots before I snapped them on.
 
Local salvage yard sells used wires for .99/ea. with a 30 day return policy.
I think the Autolite Professional Series wires sold at Advance Auto Parts (maybe other chains too) have a life time warranty which scored me a free set when I had my Mystique. I think they were $60 and you need to save the receipt. Last set you'll ever have to buy.

The Taylor wires on my SVT showed no visible signs of damage but still made the car run crappy.
 
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