Solved.
civic tach is reading incorrect. 400+rpm lower then actual.

I have a 96 gsr swapped eg sedan. Running on obd1 p72 ecu.. So the ecu is correct. In the pass, I remember I can rev up to 8000rpm. But lately for some weird reason it cut off at 7200rpm. No CEL, I jumped the 2 prong blue service connector. The cel stays solid the entire time. The only thing that blinks is the SRS light. It blinks continuously until u remove the key. So no CEL code to go by.
I'm checking for vac leak as soon as my smoke machine comesl in.
Cap and rotor look perfect, oil is fresh and up to level. VTEC kicks in at 4k.
coolant free of air bubble. No overheat.
Car was up to temp.

Mods:
Skunk2 IM
Ported stock tb
Generic header 2.5in collector
Magnaflow 2.5in cat converter
2.5in ss exhaust pipe fitted with Vibrant Ultra quiet Resonator and Apexi WS2 2.5in universal muffler.

Stock gsr intake box and tube. New filter..

Timing dead on. Car drive and idle normal 850+/-rpm. VTEC kick in on all gears. Civic tach is not off due to VTEC kick in at correct rpm.

I also have a JDM obd1 p72 ecu to tried and same result. Cut off at 7200rpm, hit rev limiter..

Can't figure out what's going on. Since there is no CEL, I have nothing to go by.

Fuel filter is 2 yes old, car driven less then 7000 miles in 2 yrs. Fuel pump is gsr OEM, not civic. Pressure is in line with FSM spec. Already tested pressure.

I don't have an external tach to try but even if the civic tach is off, it shouldn't be off 800rpms.

Any suggestion?

JDM ecu part number is: 37820-p72-003
Usdm ecu part number is: 37820-p72-a01

 

I found an old thread that someone with similar issue and he found out it was his intake tube collapsing during high rev on a dyno. What doesn't make sense to me is being a stock form gsr like from factory, using stock airbox and tube, it shouldn't collapse. Otherwise every stock gsr out there would have this problem. Correct?

 

Tach can be inaccurate more than 800 rpm in the high rpm.

My lowly D16Z6 redlines at 7200, sometimes the tach shows hitting 7K and sometimes it shows hitting under 6500 when it rev limits.

It's my understanding the stock tach tends to be unreliable after 5000 rpm or so.

May not be your issue, but could be.

ECU is programmed to continue it's normal process even when it loses the signal from the distributor in high RPM situations or so I've been told.

 

Well. I may have to look for an external tach just to compare.
i just now finished the smoke test with using a cigar. Found 3 small leak. Tps, tb gasket, and behind the tb clamshell coil. Took the tps off, found missing gasket. I had this tb bored by maxbore along time ago, he must've forgotten about the gasket. Hence the small leak. Tb gasket is on order, will arrive Wednesday. Now I don't know what to do about the 3rd leak, behind the tb clamshell coil.
I put some gasket seal (similar to hondabond but from Toyota) around the tps lip and reinstall it. Then recalibrate it, 4.5v WOT and 0.48v Closed Throttle. So it's perfectly in spec. Now waiting for the gasket seal to cure over night.

 

It is a common problem with the EG instrument clusters... especially the tach. An easy way to assess this is to pay attention to the VTEC crossover point, and see if that RPM is lower than expected. If so, this would explain your early REV limit. Another tach will tell the tale. Also, if you have the ability to datalog, make a full throttle pull and see if the distributor actually shows 8K.

 

Unfortunately I don't have a way to datalog. I am looking into an external tach. Any recommendations? I rather not invest too much on this as its my DD. I see those glowshift tach gauge for less then $50 on eBay. But don't know how accurate they are. I don't want to dump $200 for a giant 5in tach. Those just look bad IMO.

 

Small update.
fixed the leaks. Put a k&n cone filter directly over the tb and went for a test. Still bouncing off the rev limiter @ 7200 rpm.
Next up. Getting a tach to see what's going on.
Got a bouncy idle now at idle after engine is fully warmed up. I thought for certain once the leak are fixed it would go away. Already clean iacv. No fitv present. So, I don't know now..

 

Final update.
civic tach is off by at least 400+rpm at any range. External tach show redline at 8000rpm..

Solved.

 

so did you do anything to correct the internal tach? mine is way off by like 2000 rpm, tried replacing basically everything with no results

 

You replace the tach... or use an aftermarket one instead of the OE tach.

 

95 gsr swap into a 93 del sol si,
Hmmm, I haven't tried an aftermarket tach in the car, just outside to see what the engine was doing and it went to 8300 before fuel cut off, vtec at 4500 ish, iab at 5200 ish. trying to keep the stock look, I've tried 3 different clusters, new dizzy, new engine wire harness, new ecu just because, straight grounding the tach, engine revs to 8300, tach reads 6000, I have no potentiometer on any of the tachs I've gotten for adjustment, found nothing online for tachs with out them... pretty much lost on this right now and spent way too much $$$ on it...