Full boost, no codes, no power?
 

I have a '93 5 speed with ~160K miles (50K miles on 2nd engine). It has very little power at boost and I can't seem to figure it out. Please help with any trouble shooting suggestions.

Symptoms:
- Starts fine
- Idles OK (750 rpm with 15" vacuum after full warm-up)
- Goes through normal boost pattern (10-8-10 psi manifold pressure)
(can go to 15 psi with boost creep since exhaust modifications were done!)
- Slow acceleration
(Full throttle at 10psi feels not much different than mid throttle and no boost)

Things I've done so far to try to figure it out:
- Added fuel pressure gage.
(meets all specs in manual including pressure at high boost and rpm)
- Added air/fuel ratio gage.
(appears to operate correctly in closed loop and open loop modes - slightly rich
at full throttle and boost)
- Replaced spark plugs.
(may have improved smoothness, but did not correct low power issue)
- Added/replaced ground straps as recommended - firewall, battery, engine block
(may have improved smoothness, but did not correct low power issue)
- Added downpipe, midpipe and high flow exhaust.
(runs slightly better, but still no added power under boost)
- Performed poor-man's compression test.
(leading spark plugs were pulled out one at a time and listened for compression)
This showed three equal pressure spikes on both rotors indicating no apex seal failures.


Other info:
- Tach sometimes reads about 1,000 rpm higher than it should.
- MAP sensor seems to work correctly, because it will run much worse and lean out if the hose to it comes off!
- Wouldn't start for me once (after stopping the engine before it warmed up and letting it sit two days while I was reworking the exhaust) and I had to use 2 cycle oil in the spark plug holes to start it.
- Since the exhaust changes, it will sometimes backfire on deceleration and also other drivers behind me have noted the smell of gas.
- I purchased a Japanese ECU that was reportedly remapped for a car with these exhaust modifications. However, when I tried to use it, the air/fuel ratio meter indicated extreme leanout under boost as if it was not responding to the MAP sensor or the secondary injectors were not operating. I am currently using the original ECU and still have the original problem of very little power under boost.


Help !!!
Does anyone have any suggestions??
Secondary injectors?
If it's an injector problem, why doesn't it show on the air/fuel ratio meter?
TPS?

So what exactly is the problem? I don't really understand the post.

R.K.

The car is very slow because there is very little power. It runs OK, but there is no more power when the boost gage reads 10 than when it reads 0.

If you are reading the boost at the mainfold (uim) and its 10psi but the car seems like its not accelerating; it may be your clutch slipping. If your secondaries were not working then you would of popped your motor already. With the addition of the exhaust you definitly have to get a remapped ecu. Your lack of additional boost leads me to believe that you have a boost leak somewhere. Check all of your couplers to make sure that they aren't cracked or anything. With the full exhaust you should be spiking to over 15 psi and creeping close to that because of your unported wastegate. But because you are using the factory ecu you should hit fuel/boost cut. Thats all that I can think of now.

R.K.

Thanks for the thoughts, but the clutch isn't slipping.

Also, the boost will creep to around 15 if I keep my foot in it for long enough - just no power to go along with all of that boost!

I think you creeping to 15 lbs on stock setup is what caused that

Although my air/fuel ratio meter shows rich, I expected it to lean out at high boost after I changed to the high flow exhaust set-up unless I used a modified ECU. However, after I put the straight pipes in, the meter still showed rich at all boost levels - just not very much power at any level. Nothing I have done has improved the power.

I'd start with your coils (and ignition harness). Check to make sure they are working within spec.

Just check resistance in the coils?

or check for spark?

Follow the manual for checking the coils:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/testing-ignition-coils-spark-plug-wire-corroded-408014/

double throttle not opening? brakes binding? poor compression? boost leak? just throwing stuff out as the post is a bit vague

But wouldn't a bad coil cause ignition breakup rather than total loss of power? Because thats what happened to me and I replaced all three coils and now the car runs like a champ. I'm still going to install the twin power to help smooth out the higher end under high boost.

R.K.

Mahjik,
Thanks for pointing me in the direction of the ignition system! I found nothing wrong with the coil resistance checks (didn't check the ignition harness), but I replaced the spark plug wires. Three of the four wires read above spec and one of the three showed open circuit (at least by the time I got the wire off the coil).

Not surprisingly, it runs a good bit better. Still not the power that it had when new, but an improvement none the less. I'm thinking about a true compression test, checking for stuck EGR and sending the injectors out for cleaning to try to find the rest of the power.

Questions about other suggestions:
- double throttle - Could I still be showing 10 psi manifold boost if the double throttle was not opening, or would it just take a while to build boost?
- boost leak - Could I still be showing 10 psi manifold boost if I had boost leak, or would it just take a while to build boost?

Any comments or thoughts are welcome. I just need some inspiration and direction to get this car really running right.

Did you actually check to make sure that all 4 plugs are sparking? when my leading coil died, my FD boosted very quickly (unburnt fuel out the exhaust spinning the turbine) but was way down on power.....