i purchased this beautiful car from a city auction, very nice looking in and out, has 167k and starts and idles very well, not to mention its very clean under the hood. so i suspect it has been rebuilt, also the clutch feels aftermarket. i bought it with a bad alt, and immediately noticed some weird boost hesitation, that i attributed to the alt charge, changed out the alt for an s5 and works great. Still i have this boost problem. the car boosts up fine but half the time when i reach half to full boost it will studder, heavily. but also some times wont. tps??? primary or secondary fuel injectors??? my biggest fear is to run lean so i am avoiding boost all together. please lend me some advice, ive had like 7 fc's but this is my first turbo.

thanx

 

roughly what rpm range are you lookin at for this?

 

Does it have a non stock exhaust system? If so, you could be hitting the fuel cut from too much boost.

 

could be fuel cut, fairly likely

could be bad ground on the block that grounds the injectors and ecu

could be a bad tps or just in need of adjusting to spec

could be a bad air flow meter or it could just be positioned wrong

 

the rpm range is verying widely but on average about 3k to 3.5k, but just an hour ago i went and drove it and it didnt cut out at all but i stopped at like 5.5k, being a new car and all. the exhaust is aftermarket from after the cat but still stock 2.5 inch diameter i believe

 

could be the notorious 3500 hesitation for details run a search its very well documented on t2's easiest solution is is redoing or cleaning grounds

 

how do address the fuel cut? im working on the ground right now... how do i adjust the tps? assuming its not bad? and by air flow meter u mean mass air flow sensor right?

 

fuel cut sounds dangerous, can i/ would i be leaning out?

 

Yes fuel cut runs lean, which equals pre-detonation. AFM is S4(flapper style) Mass Aitr is S5(hot wire). A 87 should have the afm(flapper). Check to make sure the flapper moves without any hesitation or too much friction, keep in mind there is a spring behind it but if its very hard to open this coule possibly give you a issue, thought I dont think it would cause your problem. The best way to get rid of the fuel cut is a FCD(Fuel Cut Defender/Defencer) They are about a hundred bucks. Or you can get a Rtek which has it built in, and offers tuning as well

 

bump for other suggestions

 

im 99% sure you have a boost leak...

check you intercooler couplings, BOV and all piping..



when you replaced the alternator, you removed the intercooler, right?



your AFM, TPS, injectors are fine.

 

None of the rx7's use a wire MAF. The S5 uses a flapper that's more in a cone shape rather than a hinged door, the entire center cone moves inward.

FCD's are nice if you have supporting mods (SAFC, fuel pump, intercooler, maybe even bigger injectors). I pretty strongly suggest you avoid them if you don't have experience or have any of the above listed items.

Get a decent boost gauge, the stock unit can be flaky at times and see what it reports back that you're running. Is it gear dependant when it hesitates/hiccups? (For example, does it do it in 4th gear but not 2nd?) You're more likely to get boost creep and hit fuel cut in the later gears. I'd probably just run a few bottles of injector cleaner, replace plugs/filters/plug wires, change fluids, clean grounds, adjust TPS and try it again. There's a lot of write-up's on adjusting the TPS. I'd suggest checking out:

http://fc3spro.com/TECH/HOWTO/TPS/tps.html

 

it was like this before i changed the alt aswell, the only thing i can think is the stock blow off valve thingy is supposed to have a vacuum hooked up to it but i dont know where from... but i dont think that would create a boost leak. and i have turboed cars before so i keep my eye out for that kinda thing. but i will investigate further...

as for the mass air thing, regardless of what u call it the purpose it serves is still the same, i just want to know if it would cause these symptoms

 

It sounds like you have the 3800 hesitation, but it could also be fuel cut- you need a boost gauge to tell you if you are hitting fuel cut.

3800 hesitation is usually grounding related. Here is everything you need to know: http://www.aaroncake.net/rx-7/grounding.htm


Fuel cut is harsh-feeling, but is NOT a danger to your engine in and of itself. Fuel cut is there to save you from blowing your engine from a lean condition from overboost with inadequate fuel mods. https://www.rx7club.com/poll.php?do=...ts&pollid=3863

Fuel Cut Defensor (FCD) will help you blow your engine if you do not do the supporting mods first.

 

You can find out if it is going lean very easily. Hook up an LED to the monitor lamp connection on the test connector (search this forum for my posts on 'green lamp checker') and go driving. The green lamp should be on (ECU seeing a rich mixture) throughout the acceleration phase. If it ever goes out, back off, and find out why you are going lean. Also check for closed loop operation (lamp flashing) at steady cruise.

If the lamp stays on, you are staying rich, and it is something else.

Pull trouble codes, and correct any anolomy found. Adjust the TPS to exactly 1k ohm at idle throttle (in my car that completely eliminated the 3800 rpm hesistation). Check it for dropouts throughout its operating range. Check the boost sensor per the FSM procedure. If it is lying to the ECU, you could be running into the fuel cut below the boost pressures where it normally is supposed to come in (8+ psi). (Or, are you pulling more than stock boost pressures? At what boost level does the problem come in?)

Fuel pressure ok? Any idea when was the last time the injectors were professionally cleaned? (If either of these are the problem, it should show up in the green lamp going out under acceleration).

 

I had something similar. Getting pissed at random rpms, but only while under boost. Ended up being clogged fuel sock (in tank). Replaced that and fuel filter and it runs fine now. (well, better anyway. still needs some more work...)

I redid all the grounds thinking it was the 3800 crap, but yeah, it wasn't the grounds for me...\\

 

car have a wideband A/F? need 1 if u don't have 1. that was you can investigate without worrying to much. and well u just have to have one lol

 

You NEED a FCD. Buy one. See MAZDATRIX or RACING BEAT online for one.

The stock air bypass valve gets its vacuum from a nipple on the intake manifold. Located a few inches aft of the BAC. I've a susspision you've no ACV on the car and are using that nipple for the boost sensor. Am I right? Another honked up car.

I stole the attached jpg off this site sometime ago. It shows a red vacuum hose going from the nipple I described to the air bypass valve. You need this vacuum line.

You also need a boost/pressure gauge of some sort, even if it's just a cheap one to determine if you really need the FCD.....or fuel cut out switch as Mazdatrix calls it.