Hesitation: 3500 rpm, 5th gear, WOT
 

Read some FAQ pages and did multiple searches, but only found stuff on the 3k hesitation.

On the highway today I got a hesitation in 5th and WOT at 3500 rpm. It's like a 1 sec pause, then back to normal.

I know, if I really wanted to accelerate I would have downshifted, but I'm breaking in the new engine and didn't wanna rev too high.

I get no hesitation in other gears that I can remember. I plan on putting on my boost gauge next time I get on the highway (cheapie and I just run it through the window for diagnosis/check-up :) ).

notes:

cleaned injectors
new vac lines
harness: stripped, inspected and re-wrapped
new wires and plugs
new fuel filter, PD and lines

I had the same thing, one night I took out my FD for some runs... got hesitation at 3500rpm in 4th and 5th... by the end of the night, it went away... guess it was carbon build up... NOt sure about your case though...

If the boost test looks normal, maybe check fuel pressure?

I had some funkiness the other week that I traced down to the fuel pump not being seating properly with it's o-ring.

Dave

Took it out on the highway while the GF watched the gauge.

I was wrong. It happens a little over 3k rpm in 5th gear and did it once in 4th gear. Other gears are fine.

Here's what the boost did:

Run 1: Steady at 9. Then, slowly increased to 11. It was at this point that it hit ~3100 RPM, hesitated and the boost went back to 9.

Run 2: Steady at 9. Slowly increased to 10. Hit ~3100, hesitated, and dropped to 9 again.

This doesn't happen in 1st-3rd gear.

If you are breaking in an engine it is not recomended to be going full throttle.

It's already at 800 miles and 1 oil change, making excellent compression.

Oh, and my only exhaust/intake mods are a DP, a K&N filter and smoothed (not enlarged) ports/runners..

What are your mods? Stock computer? Boost controller? Could it be fuel cut due to boost creep?

Stock ECU, DP, KN filter. That's it.

As far as creep/fuel cut, I don't think that's it because it hesitated at 10 psi as well. I'm not even sure it went to 11 that one time because my GF was watching it and she told me that. I've only seen it go to 10...

I guess I need a more accurate boost reading to really diagnose this, so I'll try again in the light since my gauge is not back lit.

Does this sound like fuel cut to anyone? I was thinking about taking out the wastegate pill and seeing if it still happens.

fuel cut happens at 14psi and feels like u just put hte clutch down and popped in in the middle of your WOT run

^ I was just reading your thread on hitting fuel cut.

14 psi on stock ECU? I found a chart that showed fuel cut at 3k RPM = 12 psi. Maybe I misunderstood it.

Is there any way I could be having boost control issues with smoothed/matched stock ports, K&N filter, and PFS downpipe?

https://www.rx7club.com/attachment.p...0&d=1190292917

Fuel cut happens at different boost levels at different RPM with the stock ECU.

As stated above:

1000rpm-11.8
1500rpm-11.8
2000rpm-11.8
2500rpm-11.8
3000rpm-12.2
3500rpm-12.4
4000rpm-12.8
4500rpm-13.3
5000rpm-12.2
5500rpm-11.3
6000rpm-11.1
6500rpm-10.7
7000rpm 10.7

Damn, well I'm thinking my gauge might be off a few pounds and I'm hitting fuel cut. I'm going to take out the wastegate pill and see what my boost looks like and if the hesitation still happens. I'll eventually put in a MBC and use a quality boost gauge.

Sound like a good plan?

I like it.

Dave

If you are hitting it in 4th and 5th only and when the boost is getting around 11psi, it is almost definitely the stock ECU fuel cut.

Wade

Thanks for the input. I've ordered a Hallman Pro RX manual boost controller and a VDO boost gauge. Doing the wastegate pill delete in the meantime.

Correct (of course)

The reason 4th & 5th only is a clue is that the ECU has a bit of a delay before it responds with the fuel cut. In the lower gears, it happens too fast for the ECU to do anything.

I took out the pill and am maxing out at 8 psi and am no longer hesitating. So, it was almost definitely fuel cut. I guess my port matching and smoothing had a substantial effect. The stock setup really is a delicate balance!

Ok, I understand a bit better now.

You could try putting a valve in place of the WG pill and tuning it up to 10-11 psi, "just" under the fuel cut. Only running 8psi versus 10/11 is a significant drop in power.

Wade

Oh, I can tell it's slower at 8 without even getting on it that much. If you read up a bit, you'll see that I'm putting in a hallman MBC.

re
 

ummm

Sorry, I read that but it didn't sink in. :) Good luck with your adjustments.

Wade

So, it was obviously fuel cut. Now I have a couple questions.

1. Is it normal to overboost with only a DP, K&N, and smoothed/matched ports?

2. I heard no detonation. Does fuel cut in itself cause any damage to the internals?

3. On the factory ECU, how high over stock boost do you have to go to lean out and detonate? Keep in mind my fuel system is in like-new condition... most of it is new and the injectors were serviced.

Correct me if im wrong but isnt it bad to put that kind of load onto a car, especially in top gear on a break in engine?

It doesn't sound like a lot of mods, but it's possible.

Generally, no.

Very hard to say. The stock fuel system tends to hit 100% cycle around 14psi or so.

Dave