Contour Enthusiasts Group Archives Forums Modifications 3.0L Duratec ?Help tracking down the stuttering problem....Long...

I decided to take the plunge today and throw in those 3L injectors that I had. They are the light-blue injectors that some people have reported were 24# injectors.

I threw them in, and reset the pcm. I started the engine and let everything stabilize.
I put a few miles on it and then I checked a few things.

The long term fuel trim is showing about -10% (actual range was -8% to -13%) for both left and right banks.
This means that the pcm is leaning out, and most likely is the result of bigger injectors.
I cannot confirm directly that these light blue injectors are 24#'ers, but I have enough indirect evidence that agrees with it.
First, with the SVT orange injectors, there was only a little positive fuel trim adjustments, abou 3-5% or so. With higher fuel pressure (65-68psi) the long term fuel trim was about the same. 65-68psi on the 19# injectors equates to about 24# per hour output. So the two separate conditions seem to agree with each other.

The bad news. It didn't change anything with the driveability. I did a little examination of O2 sensor values with the Palm III. The O2 sensor voltages are now much richer under acceleration. They are reading abou 0.94 Volts at WOT in any gear.
When I made good power before, I was running 0.86V at WOT. This translated to a rich mixture on the dyno. These 24# injectors may be making me run too rich. Also, if I let off the gas a little to cruise after accelerating, it takes longer for the O2 sensors to start swinging in open loop than it did before.

The stuttering is apparently a misfire, but only at low rpm. This misfire did not change at all between the injector swap.
So far, I still am thinking that the stock MAF is the culprit, but I am not sure.

I need some ideas.


Here are some other things I checked in addition to the above mentioned stuff.
I've qualitatively observed the coolant temp sensor, IAT sensor, TPS sensor, airflow values, and spark timing. They values are all close enough to what I would expect in normal operation.
By this I mean that there are no 'way-out' values.

This problem did not show up when I had the stock catback system on the vehicle. It seems to have shown up around the time I put the new more open exhaust system on. It also does not seem to vary with the different changes to the intake system (like with or without a filter, pipe diameter, etc).
Lastly: The engine runs with good power once the rpms get close to the IMRC opening point. It does not have any idle problems, and if I give it a small amount of throttle until I hit 3000 rpm then it will not show the stutter issue. Basically, the stuttering seems to go away around 3000 rpms and up. Having a load on the engine does not seem to affect the stuttering at all either. i.e. I can rev the engine at a stop and it still stutters/stumbles/misfires (whatever you want to call it) when the rpm is off-idle and below 3K rpm.

I think that is everything. I appologize about the length, but I want to make sure you all have the same information I do before you begin to ask questions, or offer advice.

Any ideas are appreciated. Thanks in Advance,

warmonger
"Tom"

Interesting I am having a similar problem with my 99 2.5L cougar. I don't exactly know what you mean but stutters but my car doesn't feel like it wants to go below 3000rpms. The car jerks like 2 or three times and then when the secondaries open up the car runs like a bat out of hell.

I pulled my exhuast off and found that my hi flow sho shop cat was all eaten away to about a chuck the size of my fist. I knew it was broken but I didn't know it was that bad (oh that is my second hi flow cat to ). I got the misc chunks out, changed the oil and put the stock intake back on. No dice, the car runs the same. I am going to get a S-AFC next week to see if this will help. I know it is running rich because that is the only reason the cat would be eaten away so bad. The car must be dumping fuel right into the cat.

This is why a 3.0L swap will take place this summer.

Later,
Chris

WarMonger,

Hello. You are exactly describing the problem I am having and that others are having as well (especially with a number of 2000 svt 'tours). Please check out this link to the main thread and confirm. Thanks!


CEG thread on low/mid rpm stuttering

=-/

I wonder if it's the drastic tip-in timing retard the stock chip invokes that is causing the stuttering/bogging... just a thought.

Ok, I read through all the posts, and the problem does seem to be similar. However, I didn't have it before The week where I went to the dyno and put on the new exhaust.
I have a 1999 SVT which has always had impecable engine performance in the past.

In my case, since my engine ran fine before, something has happened to cause this issue and it is not likely to be a prom issue.
Its either going lean, going rich, or timing problems.

I tried several things to richen the fuel up because I though it was due to lean misfiring.
Higher Fuel Pressure -- No change
Additional fuel added with suplemental injectors -- no change
Now larger 24# injectors -- NO change, and running rich.

Seems to me like it is becoming a timing issue.

I wonder what will happen if I remove the knock sensor plug. If it is getting false knock readings, then it might not pull the timing off.

I think I'll go and try that now.

warmonger

I just read over the old post and was wondering if anyone was able to get it figured out. My 2000 also does the same thing. And the spark sounds sort of familer. I need to look at my data on my OBD2. What was concluded from that earlier post the chip is messed up? If someone has changed to an aftermarket chip was it fixed?

Well, pulling the knock sensor wire didn't do anything. It acted exactly the same, so it probably isn't getting false knock signals.
I am still leaning towards the MAF though.

warmonger

Is what I described above the same as what you svt's are having? Do you have S-AFC? I was reading through some posts that said that will only help at full throttle meaning since this stuttering is only at throttle points below that it wouldn't help. Someone let me know so I don't blow $300 on something that will not fix it (although I need it later so I guess it isn't blowing the money).

Thanks,
Chris

If you put 24# injectors in, dont you need to have your 'stock' MAF calibrated for the larger injectors? Why dont you try and find a 3L duratec (taurus) MAF and see if it helps? When I do my swap, im using all stock 3L stuff at first.. Just to make sure it drives ok.

Yes, I am waiting for a MAF that I ordered right now. It could be here any day. However, the problem persisted whether I had 19# injectors in or 24# injectors in. The injectors made no difference at all in the drivability issue. The injectors did richen up the engine over all, I can see the signs in all the fuel management readings with the OBDII scanner.

I will have to wait until I get the new MAF. If I still have problems then it will be off to the dyno.
warmonger