3rd & 4th gear 6500 rpm hesitation?
 

Hi everybody!

I've been having this annoying problem for months now. It seems that when I pull it on the freeway either on 3rd or 4th gear, my 7 would pull real strong until right around 6 - 6.5k rpm and STOPS pulling!!! I mean it just feels like as if the fuel has been cut off. I called Rick's rotarytwo months ago and described the situation to him, he told me that my clutch is probably slipping. So I had a Mazdatrix SS HD clutch and a RB steel flywheel put in, and the problem is still there!! :mad: Well, this pass Sunday I was reading some of the old archives and figured that I should change my spark plugs, which I did. Today it finally stopped raining so I took my car out for a test drive to see whether or not the problem has been fixed. As soon as I hopped on the freeway, there was this camaro SS and a mustang GT cutting around on the left, so I thought it would be an interesting race with the SS. By the time I got behind him, there was traffic in front. He wanted a race with my 7 so he slowed down to allow room for us to go. When I saw an opening to the right, I cut over and the race was on! I was just about to pass him and guess what? The hesitation is still there!!! :eek: NO! Well, I started the race so I can't look all stupid and stop, so I shifted to 4th and we pull even when I reached 6k in 4th. And of course the mustang GT was no competition. Good race though, but now the guy in the camaro SS thinks he's got game with a 7 running 12 psi. It really sucks knowing that if the problem wasn't there, I would've smoked both the GT and the SS and earned lots of respect. Anyone know of this problem and possibly the solution??? I'll appreciate any inputs or suggestions.

Thanks,
Adrian

The good news is that this is an easy one. The bad news is that you are really close to blowing your engine. The problem is fuel cut. I can't believe Rick's rotary told you it's the clutch. If you explained the problem half as well as you just did it would be clear to most that it's not the clutch. Besides, if your clutch was slipping you would smell it. Anyway back to your problem. At the boost levels you're running the stock computer shuts things down at various RPM. It all depends on your boost level at the different RPM.

From Lighting in a World of Thunder:

1000 26.5 11.8
1500 26.5 11.8
2000 26.5 11.8
2500 26.5 11.8
3000 26.9 12.2
3500 27.1 12.4
4000 27.5 12.8
4500 28.0 13.3
5000 26.9 12.2
5500 26.0 11.3
6000 25.8 11.1
6500 25.4 10.7
7000 25.4 10.7

I had this problem so know what it feels like. Notice the lower boost levels at 6500 rpm? Explain anything? Yup:) So now you know the cause. However this means you're probably running lean, which means every time you push your car you are running a big risk. Trust me on this one too:( The previous owner of my car sold it to me with two things. A new engine and this boost problem. So what do you do. Well first throw out that crappy Autocrapper boost gauge and buy a good unit so you can accurately adjust your boost levels by way of changing the restrictor pill in the small hose leading to the wastegate controller. Smaller the hole means more boost. It's near the air box, do a search. Or you could buy an after market fuel computer like the Power FC or Pettit re-chip. You'll need one anyway if you do any more upgrades. (I'd still get a better boost gauge.) Until then I'd advise you to lose the next race you are in.

hey thanks a lot dis1! You sound very knowledgeble about this. Now what if i do find the pill. What do I need to adjust the boost setting? Forgot to tell you one thing, one of the mechanics that worked on my car put some kinda nut by the wastegate to fool the ecu in order to achieve higher boost level...should I take that nut off?

Adrian

just curious...how come it only happens in 3rd or 4th gear though???
 

:D

Mine does the same, but it'll go past 6500, it just jerks right at that RPM. I have a rechipped ECU, so i don't know what it is. I think it only happens in 3rd and 4th (and probably 5th if you want to go that fast) because the other gears go by so quickly. The ECU dwells on the fuel maps longer in the higher gears.
~Tom

Fuel Cut is a safety feature so you DON'T blow your engine. Upgrade your ECU to a standalone that can handle mods, or you will eventually run lean and blow your engine.

Do not rev past fuel cut. Its a warning your current fuel system can't handle your added air based mods.

Get a PFC, and a bigger fuel pump. Best thing I ever did. Say goodbye to fuel cut bull, the car runs soooo much better.

goodluck,

-j

Sounds like fuel cut as previously stated.

the_saint

I have a friend who told me he was getting a hesitaion at 6000 rpm, but only when he was on the dynometer. It runs fine on the street. He has HKS dp,intake,hiper exhaust, front ic, 2 fuel inject. off the manifold elbow, EVC regulator, FMI a/f meter, and a fuel cut defender and boost gauge.He's getting 295 rwhp at 6000rpm and running 0.85 boost. From what he told me, first I was thinking. When was the last time you change the spark plugs or fuel filter?. Second thought was the fuel cut defender? I thought you should not use these? and third the fuel injectors. Maybe he's getting fuel cut on open-loop over 5000 rpm? I have Power FC and mostly M2 set up. Do any of you know what it could be? maybe a new leading coil whould help? Please help if you can, so I can pass it on to him. He's not on this forum. Thanks
Oliver

To adjust the boost setting it's trial and error. There are small pills made by Holly for carburetors that have defined sizes and fit well in the hose. Just keep going with bigger pills until you get around a safe 10 psi. You should definitely take off that foolish mod that tricks the ecu. You might not even have to adjust the boost once you do. You should research such mods before you perform them. If one guy says it a good idea don't listen to him unless you hear it a few more times from other sources. There are still a lot of people out there that don't bother thinking before they upgrade and there are plenty of shops that don't know crap and they will give you really bad advice for the 3rd gens.

Do any of you guys know about this issue with an NA FC? I have S6 rotors [with 3mm seals] but S4 irons with a big port and no 5th/6th actuators. I think my TPS is going bad honestly because it throws narrow band code at me unless I'm on the gas. Kinda lost and I'm searching right now, so I'm sorry if this is misplaced!

WOW I have this problem with my installed Pettit ECU. Glad to know before I BLOW.........Upgraded fuel pump I am looking at getting now....