3500 + rpm hesitation fixes (writeup!)
09-07-08, 05:13 PM
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3500 + rpm hesitation fixes (writeup!)
Wow, it's been a long time since I last posted on here! Anyhow, I've gotten back into RX-7's again, and this time with a Turbo II.
Long story short, this car was in a flood about ~3 years ago. The previous owner, after getting it recovered from the insurance company, let it sit in a barn for 3 years before selling it to me.
Well, this car was a nightmare. Hesitations EVERYWHERE, especially at 3500 rpm and up. Cutting out (fuel cut and knock retard), gauges going crazy, random fuel pressure, dying going around left turns etc...
I know this has been covered a few hundred times now, but I'm going to provide another good reference for those searching for a solution to their stumbling, bucking, surging, backfiring and hesitation problems, since I couldn't easily find one on here (search sucks). This is a guide for intermediate mechanics who have a good idea of how to do things to a car, not average guys trying to save a few bucks. Be smart; take your car to an experienced technician if you're not up to fixing it PROPERLY. No speaker wire-grounds, no goofy "vampire taps," or plier-crimped connections are allowed. If you don't have a digital multimeter, get one. The FSM is archaic, cryptic, and difficult to read. Visit a shop with Mitchell, Alldata or a similar program, and ask them to print wiring diagrams; they're light-years beyond the FSM's diagrams, and often they're in color for certain systems.
Preparation. Look for anything obvious. Burned wires, boost/vacuum leaks (that is a BIG ONE!!! DON'T SKIP IT!), missing pellet in the boost/pressure sensor, flood damage, poor wiring practices (speaker wire everywhere, no solder joints, etc...), and aftermarket security systems. The list is virtually infinite, but these are the major ones. Start with the obvious things, like plugs, wires and a fuel filter. No go? Start my method:
Step #1 : Clean gas. Does is smell unlike fresh gas? Even a little? Drain that nasty fuel out, and get some fresh gas, if you haven't already. 91 or 93 octane for Turbos, 87 for non-turbos. There's a drain bolt on the bottom of the tank (passenger front of the tank). Use it. Can't use it? See step #2 and siphon the lacquer-thinner-like gas out. A fuel system cleaner can actually and honestly work in certain situations. Techron (big black bottle, slim neck) actually works, and I've fixed countless cars with it. Only use with fresh gas.
Step #2 : Pull the fuel pump. It's under the carpet on the Driver's rear of the "trunk" area. We're doing this to verify the condition of the fuel tank, the hose connecting the pump to the unit, and the strainer. These hoses eventually look like tar with some nylon on it, or they crack when they go bad. It should be very stiff, and not cracking or tar-like. USE FUEL INJECTION HOSE and WORM CLAMPS!! The strainer should be a dingy-yellow color, and have NO holes in the mesh. REGROUND THE FUEL PUMP! Run the ground from the chassis to the top of the pump/sender unit. REWIRE THAT PUMP! See STEP #6. If your tank is full of rust, now would be a great time to drop it and clean it out with gravel, BB's, coarse sand or a professional cleaning agent.
Step #3 : GROUND CONTROL! Access the ECU. ALL THE GROUNDS ARE INTERCONNECTED. Finding the bad one is the challenge, so we're going to attack all of them at BOTH ends here. The ECU is on the Passenger foot well, under the carpet and the metal panel. Is it rusty? Pull the 3 connectors out of the ECU; are they green with corrosion? CAREFULLY inspect the backs of the connectors for corrosion or broken wires. While you're down there, check the connectors on the Barometer sensor. Also called the APT sensor or the Atmospheric Pressure Sensor, and will give you a big headache if it goes bad. It's in the right-hand corner, between the fan module (engine failure module? lol!), and a big connector, right next to the ECU. Your knock-control module is also WAY up there. Check its connector, too.
3a) Now is an excellent time to do a grounding job. 3A, 3G, 2C, 2R. They're black wires on mid-year 87 to 88.
3b) Open the Hood. Ground the BLACK wire on the Boost sensor. Again, only black on M/Y 87 - 88. Brown/black on pre Mid Year 87. There's a service bulletin about this on pre-M/Y 87's.
3c-1) The sensor ground on the top of the rear rotor housing. This is most likely where your problems are coming from. There are two ways to do the engine/sensor ground. Either pull the Upper Intake Manifold or cut the harness sheath near the boost sensor/filler neck (step 3c-2). If you pull the UIM, just cut the wire ring and SOLDER a new one on to the fresh wires, and it's okay to loose the plastic insulation on the ring. If the wire WILL NOT take solder, get some ACID CORE SOLDER. It'll make even the most oxidized (black) copper take solder. Also can solder certain varieties of steel/aluminum, like oxygen-sensor wires.
3c-2) If you don't want to pull your UIM, cut the sheath on the LARGE harness, that goes between the filler neck and the pressure (boost) sensor. Find the 4 large black wires (m/y 87 to 88). remove some insulation with a razor blade (slice the middle, cut the circumference and remove) to all 4 of them. Get friendly with a powerful soldering iron, and ground them to the body.
3d) Ground the engine to the chassis. The BEST place to do this is from the sensor ground lug if you removed your UIM. If you didn't, just ground the water filler neck, it's every bit as effective.
3e) The next ground is in a terrible location. You CAN get to it, but it's cramped. A flex-head 10mm Gear-Wrench works miracles! Pull your instrument cluster out. Reach behind that LARGE plastic duct. There's a ground up there, right where the steering shaft meets the chassis. If your car has gauges that are freaking out, this is extremely likely to be causing it.
3f) Run a good-sized ground from the battery ground to the chassis. Your grounding is complete.
Step 4) Replace that fuel filter! Underside of the car, near the starter. BE CAREFUL PULLING THE HOSE OFF. The system (should unless you've got a bad check-valve in your pump) holds approximately 45psi of residual pressure, for hours and hours on end. This prevents fuel boil-off during heat-soak. If your fuel comes out of the filter looking orange, replace it and re-clean your tank! After you drain the filter, you should EFFORTLESSLY (nearly NO resistance) be able to blow through it, both directions.
Step 5) Is your MAF bad? If you've got a bad hesitation around 6k rpm, replace that airflow sensor! There's a service bulletin about this one, too.
Step 6) REWIRE THAT FUEL PUMP! Get a relay a pigtail, and about 15 feet of 14-gauge RED wire. Use the existing fuel system to operate the relay's switch (ground #85 to chassis, power pin #86), in case of a wreck or fire. Run a FUSED (20a) wire directly from the battery to the relay pin #30, then directly from the relay to the pump from pin 87. DO NOT USE PIN 87a! That pin energizes when the relay turns OFF. The fuel pump's "+" wire is a BLACK/WHITE wire on the unit's harness. EVERY manual I read incorrectly states it as being Lime, which is it, BEFORE the pump/sender unit's harness, near the power antenna.
Step 7) Time for some diagnostic work. Hook up a brass 5/16" "T" fitting and a fuel gauge under the hood. Make sure it's secure and leak free (has to hold ~90psi). Look at what your gauge does as it's hesitating. Is the fuel pressure dropping? If so, and you've already rewired it and done a filter, replace that pump before you kill your engine!
Step 8) Change that Coolant Temp Sensor (the 2-wire sensor on the BACK of the water pump housing, underneath the alternator). There's a service bulletin about this, too.
Step 9) You're getting pretty deep here. Check the proper functionality of the pressure sensor, the knock sensor, the injector resistances/spray pattern. Any shop with a Snap-on "red brick" and a "Multi-1" adaptor can read data from your ECU; have them do so and look for problems. You're starting to enter the "desparation phase" by this point. Your most likely culprit is a broken wire or a wire shorting to ground, particularly on a sensor feed, or a bad sensor.
Step 10) I've seen shorted ACV (Air Control Valve; passenger-side of engine, on Lower Intake Manifold; connects to the Smog Pump) blow main fuses and wreak havoc on diagnostics. I've also seen every solenoid on the driver's side of the engine, under the intercooler/dynamic chamber short out at one time or another and turn the computer OFF when the computer tries to operate it (switches a ground), BK/WHT is power from the main relay. I've seen ignitors on the trailing coil packs short out when they get hot. Virtually every sensor can fail when it gets hot or when it's cold. Intermittent problems are TERRIBLE to find, and I wish you the best of luck on your hunt. Leave no harness un-inspected; even the ones under the seats; they all can cause major problems.
Black_Sunshine
Long story short, this car was in a flood about ~3 years ago. The previous owner, after getting it recovered from the insurance company, let it sit in a barn for 3 years before selling it to me.
Well, this car was a nightmare. Hesitations EVERYWHERE, especially at 3500 rpm and up. Cutting out (fuel cut and knock retard), gauges going crazy, random fuel pressure, dying going around left turns etc...
I know this has been covered a few hundred times now, but I'm going to provide another good reference for those searching for a solution to their stumbling, bucking, surging, backfiring and hesitation problems, since I couldn't easily find one on here (search sucks). This is a guide for intermediate mechanics who have a good idea of how to do things to a car, not average guys trying to save a few bucks. Be smart; take your car to an experienced technician if you're not up to fixing it PROPERLY. No speaker wire-grounds, no goofy "vampire taps," or plier-crimped connections are allowed. If you don't have a digital multimeter, get one. The FSM is archaic, cryptic, and difficult to read. Visit a shop with Mitchell, Alldata or a similar program, and ask them to print wiring diagrams; they're light-years beyond the FSM's diagrams, and often they're in color for certain systems.
Preparation. Look for anything obvious. Burned wires, boost/vacuum leaks (that is a BIG ONE!!! DON'T SKIP IT!), missing pellet in the boost/pressure sensor, flood damage, poor wiring practices (speaker wire everywhere, no solder joints, etc...), and aftermarket security systems. The list is virtually infinite, but these are the major ones. Start with the obvious things, like plugs, wires and a fuel filter. No go? Start my method:
Step #1 : Clean gas. Does is smell unlike fresh gas? Even a little? Drain that nasty fuel out, and get some fresh gas, if you haven't already. 91 or 93 octane for Turbos, 87 for non-turbos. There's a drain bolt on the bottom of the tank (passenger front of the tank). Use it. Can't use it? See step #2 and siphon the lacquer-thinner-like gas out. A fuel system cleaner can actually and honestly work in certain situations. Techron (big black bottle, slim neck) actually works, and I've fixed countless cars with it. Only use with fresh gas.
Step #2 : Pull the fuel pump. It's under the carpet on the Driver's rear of the "trunk" area. We're doing this to verify the condition of the fuel tank, the hose connecting the pump to the unit, and the strainer. These hoses eventually look like tar with some nylon on it, or they crack when they go bad. It should be very stiff, and not cracking or tar-like. USE FUEL INJECTION HOSE and WORM CLAMPS!! The strainer should be a dingy-yellow color, and have NO holes in the mesh. REGROUND THE FUEL PUMP! Run the ground from the chassis to the top of the pump/sender unit. REWIRE THAT PUMP! See STEP #6. If your tank is full of rust, now would be a great time to drop it and clean it out with gravel, BB's, coarse sand or a professional cleaning agent.
Step #3 : GROUND CONTROL! Access the ECU. ALL THE GROUNDS ARE INTERCONNECTED. Finding the bad one is the challenge, so we're going to attack all of them at BOTH ends here. The ECU is on the Passenger foot well, under the carpet and the metal panel. Is it rusty? Pull the 3 connectors out of the ECU; are they green with corrosion? CAREFULLY inspect the backs of the connectors for corrosion or broken wires. While you're down there, check the connectors on the Barometer sensor. Also called the APT sensor or the Atmospheric Pressure Sensor, and will give you a big headache if it goes bad. It's in the right-hand corner, between the fan module (engine failure module? lol!), and a big connector, right next to the ECU. Your knock-control module is also WAY up there. Check its connector, too.
3a) Now is an excellent time to do a grounding job. 3A, 3G, 2C, 2R. They're black wires on mid-year 87 to 88.
3b) Open the Hood. Ground the BLACK wire on the Boost sensor. Again, only black on M/Y 87 - 88. Brown/black on pre Mid Year 87. There's a service bulletin about this on pre-M/Y 87's.
3c-1) The sensor ground on the top of the rear rotor housing. This is most likely where your problems are coming from. There are two ways to do the engine/sensor ground. Either pull the Upper Intake Manifold or cut the harness sheath near the boost sensor/filler neck (step 3c-2). If you pull the UIM, just cut the wire ring and SOLDER a new one on to the fresh wires, and it's okay to loose the plastic insulation on the ring. If the wire WILL NOT take solder, get some ACID CORE SOLDER. It'll make even the most oxidized (black) copper take solder. Also can solder certain varieties of steel/aluminum, like oxygen-sensor wires.
3c-2) If you don't want to pull your UIM, cut the sheath on the LARGE harness, that goes between the filler neck and the pressure (boost) sensor. Find the 4 large black wires (m/y 87 to 88). remove some insulation with a razor blade (slice the middle, cut the circumference and remove) to all 4 of them. Get friendly with a powerful soldering iron, and ground them to the body.
3d) Ground the engine to the chassis. The BEST place to do this is from the sensor ground lug if you removed your UIM. If you didn't, just ground the water filler neck, it's every bit as effective.
3e) The next ground is in a terrible location. You CAN get to it, but it's cramped. A flex-head 10mm Gear-Wrench works miracles! Pull your instrument cluster out. Reach behind that LARGE plastic duct. There's a ground up there, right where the steering shaft meets the chassis. If your car has gauges that are freaking out, this is extremely likely to be causing it.
3f) Run a good-sized ground from the battery ground to the chassis. Your grounding is complete.
Step 4) Replace that fuel filter! Underside of the car, near the starter. BE CAREFUL PULLING THE HOSE OFF. The system (should unless you've got a bad check-valve in your pump) holds approximately 45psi of residual pressure, for hours and hours on end. This prevents fuel boil-off during heat-soak. If your fuel comes out of the filter looking orange, replace it and re-clean your tank! After you drain the filter, you should EFFORTLESSLY (nearly NO resistance) be able to blow through it, both directions.
Step 5) Is your MAF bad? If you've got a bad hesitation around 6k rpm, replace that airflow sensor! There's a service bulletin about this one, too.
Step 6) REWIRE THAT FUEL PUMP! Get a relay a pigtail, and about 15 feet of 14-gauge RED wire. Use the existing fuel system to operate the relay's switch (ground #85 to chassis, power pin #86), in case of a wreck or fire. Run a FUSED (20a) wire directly from the battery to the relay pin #30, then directly from the relay to the pump from pin 87. DO NOT USE PIN 87a! That pin energizes when the relay turns OFF. The fuel pump's "+" wire is a BLACK/WHITE wire on the unit's harness. EVERY manual I read incorrectly states it as being Lime, which is it, BEFORE the pump/sender unit's harness, near the power antenna.
Step 7) Time for some diagnostic work. Hook up a brass 5/16" "T" fitting and a fuel gauge under the hood. Make sure it's secure and leak free (has to hold ~90psi). Look at what your gauge does as it's hesitating. Is the fuel pressure dropping? If so, and you've already rewired it and done a filter, replace that pump before you kill your engine!
Step 8) Change that Coolant Temp Sensor (the 2-wire sensor on the BACK of the water pump housing, underneath the alternator). There's a service bulletin about this, too.
Step 9) You're getting pretty deep here. Check the proper functionality of the pressure sensor, the knock sensor, the injector resistances/spray pattern. Any shop with a Snap-on "red brick" and a "Multi-1" adaptor can read data from your ECU; have them do so and look for problems. You're starting to enter the "desparation phase" by this point. Your most likely culprit is a broken wire or a wire shorting to ground, particularly on a sensor feed, or a bad sensor.
Step 10) I've seen shorted ACV (Air Control Valve; passenger-side of engine, on Lower Intake Manifold; connects to the Smog Pump) blow main fuses and wreak havoc on diagnostics. I've also seen every solenoid on the driver's side of the engine, under the intercooler/dynamic chamber short out at one time or another and turn the computer OFF when the computer tries to operate it (switches a ground), BK/WHT is power from the main relay. I've seen ignitors on the trailing coil packs short out when they get hot. Virtually every sensor can fail when it gets hot or when it's cold. Intermittent problems are TERRIBLE to find, and I wish you the best of luck on your hunt. Leave no harness un-inspected; even the ones under the seats; they all can cause major problems.
Black_Sunshine
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rgordon1979
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