IWNTA20B

Just wondering if anyone has had this or maybe I've missed something.
Just out of the blue, the hesitation popped up on boost between 4000-5000rpm
It seems to be worse when cold. On the freeway in 5th I can floor it and boost will climb steadily. When in 3rd or 4th and floored, it hesitates like a fuel cut and pulls strong to redline.
It can't be secondaries. It's a remapped ECU so fuel cut is eliminated.
It's not the "pill" if someone thinks it is.
It's something stupid I've missed. Before anyone replies, nothing was touched or changed before it happened. It would be obvious to re-check.


So far checked:
no error codes
TPS checked (no error codes)
grounds checked
ECU grounds checked
spark plugs checked
wires checked
fuel filter checked
fuel pick up filter checked
fuel injectors recently cleaned
new thermo sensor ( no error codes)

It sounds like the fuel injectors are intermittently locking up but why always the same rpm? Why worse when engine is cold? Hmmm.....

RETed

"TPS checked" - what does that mean?
What's the WOT TPS resistance measure at?


-Ted

boosted1205

iTrader: (9)

.

rotary downshift

if its intermittant its electrical .. most likley ignition .. i have the same problum with my na .. i have yet to properly diagnose the problum thoe .. im asuming plugs and wires .. i know my plugs need changing neways

RETed

Go to sleep biatch!


-Ted

Wankel7

Do you have a boost gauge?

How is the fuel pressure?

James

KeloidJonesJr.

iTrader: (8)

zOMG~~~! TED??

IWNTA20B

TPS within spec idle approx .95 ohm WOT approx 5.00 Ohm
It's not intermittent, it always does it around 4000 - 5500 rpm or so.
Sometimes worse than other days. Maybe spark plug wires arcing?
CAS wires grounding against something as the motor tilts on WOT?
Just normal cruising is fine. In 5th on the freeway I can floor it and it will boost.
No jerking. It's the abrubt boost from 2nd - 4th .
Weird.

Mr rx-7 tt

iTrader: (5)

We have the same problem with a buddies TII. If you drive normal the car is fine, step on it and it kind of "bucks". The injectors were sent off to RC and flowed so it's not an injector problem.

IWNTA20B

I have every aftermarket Defi as I don't trust stock gauges...water temp...boost...fuel pressure.. oil pressure.... no EGT(wish I had it installed) .Nothing abnormal.
Fuel pressure set at 40 psi...All AN fittings...s/s lines... no leaks if anyone thinks so.
Fuel pressure does not drop.
I have an A/F gauge just to monitor idle richness....it doesn't blank out when the hesitation happens although it'd not a quick reacting gauge. It can't be the O2 sensor at WOT the O2 sensor doesn't monitor anything.
I'll keep searching....hopefully something stupid pops in my head.

IWNTA20B

This is similar.
It acts like a fuel cut for a couple seconds then pulls strong. No pinging.
It can't be the injectors... I think. Unless it's intermittently locking up.
The plugs are about 1000 miles young. I may try new ones in case it's a bad batch...never had bad NGKs. I'm willing to try anything but one thing at a time so I know what it is instead of changing a bunch of things and not knowing.

RETed

Okay, TPS looks good.

Try this test...
Unplug the boost sensor electrical connector from the boost gauge and gradually go into boost.
Does it still do the same thing? If it does, it's probably ignition related.


-Ted

IWNTA20B

I used a spare boost sensor (lots of spare parts in cases like this).
Same.
Would a coil go bad suddenly? Why only between 4- 5500 rpm? Come to think of it, sometimes lower.
Why not in 5th and boosting? Only abrupt boost from coast to WOT in 2nd through 4th. I'm going to swap parts around and see what happens. I have spare plug wires.
I don't think it's bad grounds to the coils since there are additional grounds to manifold, both coils, alt bracket, firewall and checked the main ECU ground under the TB. All snug.

myfc3s

iTrader: (2)

Did you check your grounding's? I.E battery terminal's.

Mr rx-7 tt

iTrader: (5)

Fuel cut/overboost.

https://www.rx7club.com/forum/showth...&highlight=fcd

RETed

It might not be the part that's bad, but it does eliminate one possibility.
Try and unplug the electrical connector from the boost sensor and give it a test drive to see if anything changes.


No, if the coil goes bad, it typically dies.
If it's *arcing*, then that could be the cause of your problems.


Hard to say until we isolate the problem...


Did the problem appear after you did all this regrounding?
How are you grounding everything?
Are all these extra grounds going to a single point?
Sometimes "star" grounding can cause ground loops which can cause all kinds of headaches...


-Ted

IWNTA20B

Well, I'll try unhooking the boost sensor.
Did I say it sounds like a rev limiter? It points to an electrical problem but so far everything checked out. I'll clean out the grounds for the coils at the same time.

As someone mentioned earlier about the battery post...that was the first thing I checked. It's an FD alt. and the battery reads 14.5V at idle so it's not the alt.

IWNTA20B

Anyone wants to add what they think it is or have had similar problems?
You all bumfounded as I am?
I'm making a list of "what to check" besides noted above.

Tech_Greek

I just had this exact same problem, it turned out to be a crappy ground that I forgot I ghettoed to get home (and racing with a bad ground sucks when your car bucks only in certain gears).

I figured it out when I saw that my ground was like, barely making contact with the metal and that when I touched it my engine died...your exact same symptons happened to me, it was the upper intake manifold ground for my case and dealeo.

My car would boost fine in fith gear as well, only because the engine didnt move enough to make the ground wiggle.

CHECK THE GROUNDS!

FC3S Murray

iTrader: (7)

MAN I have the same problem!! Turbo II S5 street ported. all new grounds and "circle earth" ground kit. Fuel is fine. TPS is a legit. WOT in 2-4th bucking around 3800 to 5000 rpm.

I just swapped the engine due to blowing up the last one and i never had this problem before.

I heard about re grounding the ecu at it's points. Two that go to the top of the engine and the ground to the boost sensor. I am going to try it today but do think it will work?

Like i said evrything else is OK on my car, just pisses me off!! so close to being completely finished with this swap. HELP!!

bigdv519

iTrader: (3)

Same here.

A buddy has a S5 TII, with rebuilt 3mm large streetported engine. F-con + GCC, RB exhaust, intake. Bucks in 2nd, 3rd and 4th gear under boost. Never in 5th. And always more when cold. Some days in doesn't buck at all, while some days, its a rodeo.

Another buddy has a built S4 TII, streetported blah blah blah...bucks only under boost. Mostlying in 2nd, 3rd, and 4th gear. Some days worse than others, some days, nothing.

FC3S Murray

iTrader: (7)

FIXED IT!!
I ended up doing my own "circle earth" grounding system with some 8 gauge wire. Goes from negative terminal to driver strut tower to engine to UIM. then from UIM to firewall and also to chasis under TID. What I did was tested the resistance on the ground for the secondaries and it checked good. But in a move of last desperation I put the ground from driver tower to engine on top of the secondary fuel injecter ground. No more hesitation!! Hauls ***! It was wierd that the original ground checked good too, goes to show more grounds never hurt. keep that resistance at bay. Try it out bigdv

SureShot

I'm still troubleshooting my new high boost mis-fire.

First it was the AFM (resistance values low & non-linear)
I drilled an access hole & cleaned it. That helped for a while then it came back.
Cheaned the inside PCB on the AFM again. It got worse & undriveable.

Put in a temporary 929 AFM & compensated the S-AFC down 40%.
That work great for a week, then it came back again, mostly on hot afternoons.

I beefed up the grounds when I rebuilt the motor in November, but I guess I'd better recheck them and the TPS next.