Rough Idle and slow acceleration

[Jerome]

So, I have a 96 SHO. Cams are welded, new coil packs, plugs, fuel pump, cam and crank position sensor. One day last week I started it up and it idled rough. The acceleration really sucks, and it'll surge sometimes when accelerating. After that happened I changed the fuel filter, but it still does it, and not CEL has some one. I've put close to 200 miles on it since it started this. Any ideas?

 

[sperold]

Read the codes, both active and stored.
The regular culprits for slow acceleration and no codes are:
1.) crank position sensor dying, or clearance has been altered
2.) timing chain jumped a tooth during shut-down.

 

[Jerome]

Thanks. I've changed the Crank sensor, but I will look into the timing chain.

 

[E1]

Coil.

Bad Coil.

On the other hand it might be a coil.......

96 and 97 computers are as dumb as a box of rocks. They frequently will refuse to throw a code for a bad coil. One trick is to remove the front appearance cover and, with the motor running, unplug one of the front coils. If two coils are off line it makes it more likely that the computer will catch the fault and throw a code for BOTH coils. You knew which one you unplugged, so the OTHER coil code is the real culprit.

(Example. Car idling poor. You unplug coil #8 and the car begins to run REALLY poor. Let it do so for a couple minutes and fight for its life. If you are lucky, it will set the Check Engine Light. At this point, pull the codes. You get a P0303 and P0308. You KNOW you unplugged #8, so the offending coil is #3.)

Option B. If you unplug a coil and the car runs exactly the same, do a happy dance! You found the bad coil and it was up front!

Did I mention it might be a coil?

;-)

 

[Jerome]

It shouldn't be a coil. I replaced all of them and the plugs less than 5000 miles ago.

 

[E1]

You're right - It SHOldn't be.
But it most likely is.

Are they Motorcraft coils or aftermarket coils? If I had a nickle for every time I saw a brand new coil crap the bed I'd be rich.

Try the test I suggested. It might get you a check engine light.

 

[sperold]

Another thing to eliminate is the chance the spark output (spout) connector jumper has been taken off, perhaps by accident or when the timing was checked.
Taking the connector off, sets the timing at 10 degrees before Top Dead Center, which is not great for performance.

There may be 2 of these connectors in your system, so ask around where they are and take a look.

It is a long shot, but it is another of the things that affects performance, but does not turn on the light.

 

[GEN 3 SHO FAN]

I owe some money to Eric. I bought some coils (a pack for 100$ can.) directly from China when I got the car. Bad idea, I have misfires at idle and the computer can catch which one it was. I think it was factory rejects because they all have a yellow painted mark on the plug... They also have a thinner rubber part. The guys sold them as DG465 (Motorcraft) but we can understand they are not with a rapid visual inspection. Coming with a lifetime warranty (yeah well they aren't sold anymore).



So I finally put Visteon ones (european Motorcraft) from Alanis deals and they work great. There is so many quality grades for this part... Here is some good brands I found with part number.

Ford F6DZ-12029-A
Ford F6DZ-12029-AA
Ford F6DZ-12029-EA
Ford F6DZ-12A366-A
Ford F6DZ-12A366-AB
Ford F6DU-12A366-AC (recent batch)
Motorcraft DG-465
Visteon VP4U6U-12A366-EA
Airtex 5C1126
Wells 5C1126
Delphi GN10300
ACDelco F-522
Denso 6736016
Standard motor product UF-162

I remarked that ones with brass parts seems of better quality (tooth and screw holes).

Have you changed the spark plug seals ? (small gasket all around each of the plug wells) Even if you bought good coils, if you have/had oil on the plug well this can cause misfires messing up with spark plug which will absorb it and ignition coils doesn't like that too. Oil begins to enter in some plug wells after I welded the cam because gaskets were original ones (of course, after I put new spark plugs and coils ?$!&).

ECU never throw me a code for a coil, instead it gave me a P0172 "System too rich (Bank 1)". In fact, I had oil in wells of the front bank.

I recently had some idle misfires and feared that I still have oil there but I finnaly realized that I forgot to thighten my intake rubber pipe on the MAF... :S

Hope it will help,

 

[SHOMEX]

If I were you; I would follow E1 (Eric) advised, he is one of the persons with most knowledge on the v8 sho.
My guess its a coil too.

 

[Jerome]

So I tried the coil test and nothing. I just got the code for the coil I unplugged. I haven't gotten to checking the timing yet. I will do that this weekend.

 

[GEN 3 SHO FAN]

It doesn't take many oil in plug well to create problem, have checked for this ?

Which brand is yours coils ?

It can be also a intake leak, too much air entering can cause misfires.

A close inscpection of the small fuel regulator hose can be a good thing too. If you forgot to plug it, it will let enter more air in the intake and not rise fuel pressure when needed... (When the problem started, just after you changed your rear coils ?)

 

[Izzmo]

Can't believe no one has said this yet...

Check your throttle position sensor. It can be completely bad (the potentiometer has a ground voltage) and the car still operate, yet have terrible acceleration (surging as well at stops or in park/idle), and bad gas mileage.

It's cheap.. like $20, at around $30 for a lifetime warranty one. The test is easy too...

 

[Jerome]

I don't think it was any of that. I think it was the mass air sensor. I had an extra and swapped it and now it's good, for now. I'll run it for a few days and see if anything comes us.

 

[98SF19]

I don't think anyone suggested TPS or MAF since OP said no CEL.

 

[stephen newberg]

Its also not the common characteristic of a bad MAF. With that rather than surging, hard starting is the more common initial indicator.

pax, smn