Help!! Hesitation on a FD
 

I will appreciate any inputs on a little trivial problem I been having with my 93 Rx-7. Its been driving me nuts ever since bought the car in 1999. I got a R-1 model with 50K miles bone stock when I got it. The seller put a new fuel filter assuming it was going to take care of the small hesitation it had. It didnt. When I first start the car in the morning it runs perfect, without any hesitation. As the engine warms up and it reaches operating temp. (double throttle opens) the hesitations starts showing up. In any gear as the RPM`s start to climb 1.. 2.. 3... (theres the usual boost drop and then recovers whith the typical twin turbo sequential hesitation) everything is fine until it gets to 3500-4000 rpms; as the rpms climb theres a slight hesitations that last for less than 1/2 second then recovers then keeps climbing then it happens again for the same period of time. It does this 3 to 5 times before reaching 7000 rpms. It feels like a bucking. If you upshift it happens again. The factory manual calls it hesitation; not to be confused with a surge. As the engine gets hotter the more noticeable and frequent this happens. I am not sure if is the computer retarding ignition due to knock or fuel cut off. The car is almost all stock with the exception of a K&N air box filter an stainless steel fiberglass-pack muffler. I run stock boost (10 psi) and i have no engine computer codes present, I checked the fuel pressure and is at around 36psi and during acceleration i climbs about 10-15 psi higher. I have installed an Autometer Boost, Air/Fuel and Water Temp. gauge, also a GReddy BOV and turbo timer. All works fine. I always use 93 premium gas and change the oil regurlarly. The dyno figures are about 15% less of what I spected but the charts (and gauge) show the car running rich during acceleration. This got me puzzle beyond believe, the dealer has no idea what could it be. I you have any advice, please reply and thank you for reading my boring story.
:boring:

I seems like you have the fabed 3k hesitation, do a search on that, tons of useful info/links

for starters add 3~5 more ground wires, use good wire 4 or 2 guage fattys

also the apex pfc is known to get rid of hesitation

Yeah, replace the ECU. that will fix it I hear. and grounding will help too. I did some grounding and mine is now merely a phantom that rarely is seen. I have a stock ECU still, waiting for the EMS till july.

If you feel the hesitation at 3500 RPM then this is completely normal and extremely annoying. However, if it's at a higher RPM then you are most likely experiencing a fuel cut. Your fuel filter should be changed every 10,000-15,000 miles. Also, try changing your spark plugs and wires. NGK makes great wires for the FD and the spark plugs only last 10,000 miles.

To get rid of the 3500 RPM hesitation try using a ground strap or getting the A'pexi Power FC and Commander (ECU). The Power FC will definitely get rid of 3500 RPM hesitation.

Try taking your car to Pettit Racing. They have an awesome reputation.

www.pettitracing.com

When you say ground more. Where exactly do I put it and what wires do I use?

Get a 4 gauge wire and place one end on the throttle body, the other end to the chassis. Remove the paint if necessary for a good ground. Get another wire, place it on the bottom of the engine and the other end to the chassis. Get another wire, place it on the alternator to the chassis. You get the picture now. Anywhere that is connected to the engine and ground it by touching metal like your chassis.

Thank you very much for the pointers and for your help but I'm pretty sure the hesitation is not the secondary turbo being prespool and then comming on line. Like originaly posted during pre warm up the car funtions perfectly. It has the 10 - 8 - 10 psi boost but during that last 10psi the car lightly bucks several times before reaching 7000rpm. The boost does not drop but it feels like a cut off. The factory manual does not mention any cut off just timing retardation. Also I have about 3 grounding straps hook up, new fuel filter and new spark plugs. The wires are the stock ones but I dont think is the wires because when the car is cold it has no pass 4000 rpm hesitation only after the double throtle opens. I have been researching from day 1 everywere, I believe I got all the basics out the way. I had Rx-7s for the last 10 years. The first was a `79 seven, I rebuilded and street ported the 12A added a Holley 650 with RB heathers and elect. ign. 9500 RPMs need not to say more. Then I got and `87, put heathers and intake; swallow and injector atomiser and blew and apex seal, took that engine out myself and dropped an `89 GTU engine and sold that for the `93 I got now. Several guys that work on their cars come to me for help too, they have rotarys mitsus, toyotas, domestic, bikes, boats; you named. But I could use all the help anyways, maybe someones ligth bulb will lit and help my solve this puzzle. Im new to this Forum and i post my help anytime I can.Thanks.

Have you tried switching out the ECU with another stock one?

Also, have you checked your batter terminals and all power and ground cables? It almost sounds as if you are getting a short of some type somewhere causing the entire system to hick-up the way it is.

I dont have any other ECUs to try. I guess Ill have to pay $$$ for one and cross my fingers :( ...Ev7

Unless you wanna wait until I get back down to Miami in June. We can make a small BBQ out of it with some of the guys and you can swap my stock ecu that is collecting dust with yours at the same time :p:

You also need to check/replace the ground at the junctio where the cat meets the catback. Often, this one is torn or gone all together.
Also, you must reset the ECU after you do all this. Remove the negative from the battery and hold the brake pedal down for 30+ seconds. If that doesn't work, take the panel off the and actually disconnect the wiring harness from the ecu.

If the grounds do not work, check the condition of the belts. replace if necessary. Also, check for proper tension on the belts. If you need the specs, let me know and i'll post them.

If that doesn't seem to solve it, you might look into your injectors. Either they are leaking or clogged. To start, try running good cleaner through the gas, either BG44 or Chevron fuel system cleaner. If you are really motivated, remove all of them and send them out to RC Engineering for cleaning, blue printing and overhaul. If you do that, you do need to replace all 8 O-rings. You can only get them from Mazda, and they are high dollar.

anyway, hope all that helps. if not, post again and we'll try a few other things.

High RPM hick-ups
 

As a matter of fact I bougth my seven in Kendall, at a shop that sells 7`s & 300`s. A BBQ sounds good or if you ever come to Tampa, we go to "the Mons" my treat :D ....Ev7

:)
Hey, WHERE in Kendall is the shop? Do you remember the address? I lived in Miami for 15 years, but haven't been down there in 2 years. I swear I can drive around Miami with my eyes closed :p: