Just put some 850cc injectors in as Primaries (replacing stock 550cc primaries). Followed the advice on the Forum here after searching (multiple times). I believe the installation is fine and the settings in the PFC are correct.

Changed flow rate for Pri to 850...
Changed the injector pulse width compensation to 65%
Changed the delay on the primaries to +0.04ms

Car runs great under acceleration (even moderate accel.)

Here's the deal...

Idle is pretty rough and all over the place 1000 to 1200 rpms regardless of what I program into the PFC idle speeds

and worse - when off throttle and under low load - the car bucks like a bronco...

Any insights?

 

Might be something unrelated to PFC. Check the TPS voltage readings (you can do that through the PFC) and see if the IAC can fix it. If its not that you may just need a tune.

You may just need to retune it. I have 850cc x 4 and recently returned my car to the base mod map. At WOT the car is fine, but when I give it very little throttle it tends to buck like you describe.

 

Possibly could have hooked up (or forgot to hook up) something wrong when putting things back together?

 

Thanks for your input guys....

I spent today checking the work and screwing around on the PFC Commander. The car is running great actually under boost and WOT - I guess we get to a stage were we keep modifying and enhancing these cars and this is what happens..... it's a labor of love!

Still no joy on the idle (although I did get it to settle down a little) - it is still sputtering at idle and when no load is on the engine while cruising.

I'm pretty sure everything is back together properly - I'm fairly certain that the PFC is set up properly. Plugs are fresh (although they are Greddy racing 10s). Steve Kan just tuned the car fopr me a couple of weeks ago - BUT with the stock 550cc primaries in place.

I think Gamezilla is right on the money - It just needs another tune-up. Must be some subtle differences in the fuel maps between the two different injector sizes - even with the compensation provided by the PFC..... go figure!

Smells rich at idle as well...

 

Mine does the same exact thing. Lumpy idle, but it takes about 5 secs for it to cycle between bounces. I thought it was a vacuum leak at first, but its not like any vacuum leak I've ever seen. Starts at 1k. Takes about 3-4secs to creep to 1.5k, then drops instantly to 1k again and starts all over. Also - between 20% and 40% throttle there is a big hesistation point. Mine also backfires sometimes.

 

You really have to redo your idle and low speed cruise area of your fuel map due to being very rich with the 850s. That is the problem with going to large primaries.

 

Can you keep the 550's in there and go to 1300 on the secondaries ?

Tom

 

Yes, or use 1200s as those seem to be more reliable. I run 550/1200 and at 347RWHP INJ DC was less than 85%.

 

I already have my 850's bored to 1300 and waiting to install them. Should I try the 550/1300 and see how she does with the PFC ?

Tom

 

Thanks Chuck - I think you are right and I had a conversation with Steve K a couple of days ago and he confirmed that it could be the map is too rich in certain areas with the new Primaries in place. Certainly seems this way to me.....

Here is something interesting though...... I'm currently getting about 200 miles out of a tankful of gas which is 100 miles less than I used to get before I did the fuel system upgrade.... Steve told me that was "way low" and that he had tuned some cars to get much better mileage - well into the 300+ out of a tank.

Now - I know it depends a lot on how you drive and YES I like to get on the gas occassionally - can't help the rush of 400 rwhp.

I'd be interested to hear what mileage other people are getting out of their modified FDs - might be a good idea for a poll?

And yes Tom - I had 550cc (stock) primaries and RC'd 1300 secondaries before I upgraded to the 850cc primaries - worked fine - really!

 

I'll second that. I had 850's put in my primaries (still using 850 secondaries) and I also experience the exact same drop in mileage. I get almost exactly 100 miles per half tank of gas, or around 12-13mpg. Before, I was getting 18-20 in the exact same trips to work (I check mileage religiously...). I also had to return my brand new engine after only 8 or 10k miles because compression had become very low. Turned out the internals were described as being more carboned up than 100k mile engines. So my advice is to take care of this quickly or you can actually do damage to your engine! I'm currently running Amsoil gas treatment through all my tankfulls of gas to try to keep the carbon down until I can get a proper tune. Supposedly it's exceptionally good at removing carbon.

I completely didn't expect this as I also adjusted my PFC percentages which seems that it would correct the maps. But I too have the misfiring problems you describe. Fantastic on WOT, but anything less sucks.

I spent some time on the dyno, but unless you have deep pockets it's difficult to tune anything but WOT. So I bought the AEM UEGO and was going to fix this once and for all.......well everybody's heard me bitch about that POS. Hopefully some other brand wideband will help me take care of this. Point of all this rambling is that I think as cheap as they are, all of us with highly modded 7's need to bite the bullet and put in a wideband so that we can tune these things like they need to be. CEWRX7R1 is proof that a little time spent analyzing logs can leave you with a fast car that still has fuel economy and runs better than it did from the showroom....

And thanks Chuck for your posts on tuning in the areas other than WOT. I'm saving all those posts and once I get a working wideband I plan on following in your footsteps!

 

Thanks Silver Bullet

Tom

 

Wow tail.... That is a story I don't want to experience up close. This is my second rebuild this year! and the thought of going back to the drawing board is not attractive at all.

Unfortunately, I don't have a datalogit OR wideband so I'm thinkin' (at this stage) I should probably go back to the 550cc primaries until I can get a good tune...

I drove it today again to work (85 miles round trip - mostly highway) and it's definitely running rich and bucking under no or light loads. Damn!

 

Yeah, I'm not trying to scare you and I may have some totally unrelated problem. But I think it was because of putting in the 850s. One final thing you can take a look at...is your tailpipe BLACK after a few days? As well as the back of the car? My tailpipe's so black it doesn't come off when I wash it anymore. Luckily for me, I have a black car....

 

Rusty what is the highest duty cycle you ever saw with the 550s?

 

Hey there Surge! (Yanni)

Before I did the 850cc primaries and I had just the 550cc primaries and 1300cc secondaries I was seeing duty cycles in the very early 90s.... on the PFC at high revs. and boost - 17 lbs of boost over 7K rpm.

Now with the 850cc primaries in place the same conditions yield high 70s, early 80s for Inj. duty cycles.....

 

Hello Rusty!

Can you put the 550s back until you are ready to have it retuned? Maybe inch the boost down to 16.5 as well
I wouldn't be worried about low 90s but 17psi on pumpgas is kinda up there though haha. I think I told you but when I went to the 1/4 strip to test out steves tuning a few days after I saw 98-99% at the track and then 100% on the way home. I think high duty cycles for a short time is ok but 97% should probably be the max you see for safety. 100% could mean any amount of leaness or maybe none at all

Have you heard any news on steve's tuning at pettit? I'd appreciate if you could let me know if you find out about that : )

 

Sorry - I should have clarified....

Yeah - I've been thinking about putting the 550s back in and I still might do this - I've kinda been waiting to see what happens with Steve's tuning session here in S. FL or somewhere else... Steve told me he was lining up some tuning in Atlanta, GA and another session in AL (I think) - in addition to the session he was considering for S. FL (Pettit).... Haven't heard anything or seen anything posted here on the Forum OR in the SE Forum... might have to make some calls today and see what the story is.... I'll let you know.

As far as the 17 lbs on Pump gas....... yeah, I absolutlely agree - not smart nor for the faint of heart - so I have only been using the low setting on my Greddy Profec B since Steve tuned the car last month. This gives me around 0.85 bar or around 13 lbs of boost on the PFC - by my calcualtions that's a healthy 350 or so rwhp....plenty of fun!

 

hey guys, I finally got my car sorted out and am having some of the same problems as the rest of you. I did not have these problems with 550/1200 but have them with the 775/1200 setup. I went 775 instead of 850 to avoid this but it seems as though I got hit none the less.

I am running real rich at light load(high vacuum numbers). For example; if I free rev the engine in nuetral it is real rough and misses from being to rich. If I am cruising and lift the throttle ever so slightlty as to increase vacuum over 500mhg, then it goes rich and runs rough. I thought I had a pinched injector o ring at first. I thought that when the vacuum got high enough in the engine, it was pulling fuel around the oring cuasing the motor to get unmetered fuel. I can pull as much fuel as possible and it will not get any leaner.

I pulled the entire fuel rail and injectors. What I found was that RC engineering used the wrong size orings on the primary injectors. They were the exact same as the ones on the secondaries. I went down to maztech and bought the OE ones. They fit perfect. Problem solved, right? Well no not at all. After putting it all back together and driving it, it behaved exactly the same. AT high vacuum the car goes rich.

What I have determined is that there is a minimum duty cycle that the PFC allows. Anything lower is 0 (off). This duty cycle is around 3.2%. If you try and pull more fuel, it makes no difference. It will not get any leaner. Evidently there are times such as light cruise with almost no throttle opening or free reving the motor that require less fuel than is possible to give. The larger primaries just can't go low enough. Every where else the car runs great. Pulls hard and climbs smooth.

What i am trying now is to introduce more idle air to go with the fuel. If I can not get less fuel then maybe more air. I also wonder if turning down the fuel pressure at idle will help. I sure it will but what affect will this have else whrere?

If anybody can confirm the minimum duty cycle for the pfc, this would be great. Also, My pfc seems to be working fine except one thing. If I go to monitor mode and select 8 items. They are all frozen when I display them. 4 items works fine as does 2 and 1. Only 8 causes the display to lock up much the same way as when connected to the datalogit.


mike