Tim McCreary

Got a question. Here is the situation. I got my car running and had a hesitation. Every time the car would hesitate, the A/F gauge reads lean, then when it comes back to green, it pulls again. This happened from about 2k to 3.5K.

I adjusted the AAS and backed it out 1 full turn (Street ported motor). The hesitation remained, but the surging stopped.

I knew the battery was not the best and the ground connection was not tight, so I bought a new battery. This helped lessen the hesitation, but did not eliminate it.

I then took a 16 gage wire directly from the negative terminal, tied at the ground connection at the firewall, then directly into the car and bolted to the side of the ECU.

After this, the hesitation is almost completely gone, but there is still a "holdback". As I ease on the throttle coming from 2K to 4K, the A/F runs solid rich until 2500rpm, then it goes lean and stays lean until 3000 rpm. At this point, the gauge reads rich again.

If I ease on the throttle even lighter, the guage bounces back and forth from lean to rich from 2K to 2500rpm, goes lean again until 3K, then bounces again afteward.

Anybody know what the problem might be? I have also bypassed the 1K resistor that is inline with the fuel pump, so it is running full voltage all the time.

Thanks,
Tim McCreary

FormerPorscheGuy

Check out this post in the archive.

https://www.rx7club.com/showthread.p...ght=hesitation

Matt Hey

The grounds are a good idea. I ran one from the end of my downpipe to the body for my O2 sensor as well. I had hesitation followed by backfiring and a cloud of black smoke. The grounds fixed it. I do have a PFC which supposedly helps with hesitation too.

rynberg

I would also consider the o2 sensor as the potential source of the problem. If you have over 60k on it or so, I would replace it before you start messing around with a lot of other things. You can get an exact replacement from www.oxygensensors.com for $46 (part number 250-21020 for the OEM style with wiring harness).

Tim McCreary

Along with the O2 answer, I have hooked up two A/F gauges, one in the gauge pod (Phantom Autometer) and the one connected to the J&S Safeguard. Reading differently at idle now that both are hooked up, but otherwise reading the same as it was before. Not sure which one I want to keep.

Does both hooked up affect the computer sensing the O2 sensor readings?

Also, It almost looks like the ECU is programmed to go lean from about 3K-3.5K rpms. Not sure, but it is consistent in how it reacts.

I believe I do have a brand new spare universal O2, so I will put it in first to see if anything changes.

Tim

PS: New fuel filter, new platinum plugs, new plug wires, motor was rebuilt 4k miles ago by KDR and streetported.

skunks

please dont use aftermarket a/f ratio gauges, use only wideband.

InsaneGideon

Tim, how lean are things getting according to your A/F gauge(s)? Is it near full lean?

You can't really trust the A/F readings much since the sensors have pretty much an off/on relationship around stoichiometric mixtures. They can tell you if you're above or below that, and that's about it. That's how ECUs use them, which is primarily when you're at very light load (cruising). They're heavily affected by temperature, age, and manufacturing tolerances. So they're terrible for tuning. This is why so many people on here tell us to spend an arm and a leg on a wideband setup.

As o2 sensors age, they read slightly lower voltages which the ECU interprets as a leaner A/F ratio. So the ECU compensates for the worn sensor, causing you to run rich. It will kill the gas mileage on an econbox as well, which is why Bosche runs magazine ads reminding us about this fact.

If the A/F meter reads anything in the lean half of the gauge while you're under power, your fueling is in trouble. Check that your fuel pump can hold the specified static pressure.

Tim McCreary

I can understand that a wideband is needed to fine tune a high performance modified car, but I am just trying to get the motor running at an acceptable level of smoothness and reliability. It concerns me that the A/F ratio is changing under the same RPM range when I feel they should not be. Logically, there is no reason that the fuel should go lean unless other things are happening at the same time to affect it. (grounding, fuel pressure, fuel pressure relay, fuel pump resistor, relays kicking on or off, others unknown)

The Autometer is brand new (gift) as well as the J&S came with the unit when purchased (NEW used item). I am only using them mainly to determine whether I am getting lean under full boost (which I am not), but my concern is that no matter what, from about 2500-3500rpm, there is a difference in the readings. If I start at Idle and pull lightly up the rpm's, the gauges read rich until 2500 rpm, then either go completely lean or bounce back and forth from 2500-3500 rpms, then goes rich again until redline.

The meters bounce pretty much at any rpm when cruising or light throttle which I deemed as normal. When I come completely off the throttle, the gauges read completely lean or shut off lights (assuming no fuel entering the chamber when throttle is off). As the RPM's reach idle, the gauge bounces right back to rich at idle.

I understand about the wideband, but I am not a rich kid with money to burn trying to make a monster car. I have a family, two kids, and purchased the car with a blown motor. Since then I have purchased a rear ended car with rebuilt motor and did the motor/tranny swap.

My goal is to make it a daily driver, not a street rod. I have always been obsessed by the rotary engine and have owned 6 other RX7's. This is the first of the 3rd generation type. Working on these car's is my hobby and obsession. My hope is that I do not have to waste my time troubleshooting problems that other people have already found solutions to.

I plan on replacing the O2 sensor this coming week and see if anything changes from there. I only want to make one change at a time so I can determine what the root cause is.

Thanks for the help, any other comments?

Tim

dubulup

Are you running the stock ecu??? (sigs. turned off...)

Try unplugging the O2...before I get flamed, it's only for leaning out A:F while cruising to get better emissions and mpg. It's unbelieve how much better my car runs without it plugged. I've been running like this for over a year, and even made 24mpg on a road trip

Tim McCreary

I will give that a try, but does that also throw a signal in the ecu? I will have to check.

Tim

InsaneGideon

I'll emphasize what I asked before, useless crap about the wideband O2 deleted :

If the (non-wideband) A/F meter reads anything in the lean half of the gauge while you're under power, your fueling is in trouble. Tim, how lean are things getting according to your A/F gauge(s)? Is it near full lean?

Check that your fuel pump can hold the specified static pressure.

It is possible having 2 gauges is loading the sensor causing it to read a bit lean. But those gauges should have very high impedance inputs, so let's forget about that for now.

DCrosby

1) If you are running the Apexi Box, get the car to a tuner and he'll iron out your issue, if you've got a stock ECU, Join the Club there's 1000's of 7's that have the same problem you have...

2) Stop looking at your stock AFR Gauge... It's useless... If you want to know what AFR you're running get a Wideband, other than that the stock O2... is not going to tell you anything and the stock ECU Ignores it except when in closed loop mode (0-20% TPS and 35+MPH)(Roughly)

Even then when you remove it from the ECU it doesn't throw a code since you disconnected it, I guess it differentiates between diconnected and malfunctioning...
Who Knows, but no the ecu won't give you troubble, and goes to it's default programming...

Tim McCreary

Just to clear up some things:

I am only using the A/F gauge to determine what the O2 sensor is doing, (not "Tuning the Motor for Maximum Performance" as possibly implied). Because it is a 1 wire stock O2, all I will get for information is LEAN or RICH. I understand this and it is still excellent information for troubleshooting problems, not necessarily tuning the engine. Both gauges independently and jointly show the same information at the same conditions, so neither of them are "faulty or junk" meters. I understand that I need a wideband O2 to tune fuel maps properly, but with a stock ECU there is not changing them without adding a piggyback which I do not have at this point.

My goal is to get the car running properly before tuning properly (getting an aftermarket computer, future mods, etc) because if I cannot get the car running correctly, it makes no sense to change other components and chance blowing the motor.

dubulup made the suggestion to unplug the O2 sensor and I did that this morning. I went for a run and had the hesitation. Very obvious and very apparent every time. I then disconnected the O2 sensor and went one step further by connecting the A/F signal wire to the O2 sensor.

I started off slowly and guess what, NO HESITATION OF ANY KIND. Not only did I see no hesitation, now my gauge is reading rich during light, moderate, and strong accelleration up through 2,000-4,000 rpms every time. No bouncing and no hesitation.

I believe that the signal sent to the ECU is then causing the ECU to adjust or overadjust the fuel injectors for conditions that are creating the hesitation. My next step is to replace the O2 sensor and check again with it hooked up. This is making me lean towards the fact that the ECU programming logic is bad from the factory and the only true permanent resolution will be replacement with AEM EMS or PowerFC.

For now, I am running without the O2 hooked up until the new one arrives to replace it.

My other thought is to hook up a 5th gear switch or a 4th and 5th gear switch to engage the O2 sensor during that time only, eliminating the hesitation I see at startup through first, second, and third gears.

Tim

Tim McCreary

Just to reiterate or confirm, when I am at 3/4 to full throttle I am reading a solid rich mixture. I do get a blip at 3500 where it goes lean and then rich again and this is the hesitation. Not under full boost at that time, only at about zero on the boost gauge. I don't think that I have any problems during boost. I appear to be running pretty rich under boost and throttle. (Also confirmed by my whopping 12 MPG around town).

Tim

ZoomZoom

iTrader: (2)

Injector transition from primary to secondary.

InsaneGideon

Hold on a sec. You're saying both cases here, the O2 sensor was disconnected from the ECU? But connecting the A/F gauge(s) to the O2 sensor (which is still disconnected from the ECU) rid you of the hesitation?

During the first quoted case, when you were getting the hesitation, were the A/F gauge(s) still connected to the ECU, even though the O2 sensor wasn't? Because it is possible the gauge electronics are in fact feeding voltage (noise) to your ECU, fooling it into thinking you're rich.

Regardless, this probably is, or is related to the famous 3kRPM hesitation.

Tim McCreary

New information. Got the hesitation again when I went to work tonight. ONLY at around 3500rpm under moderate to strong accelleration. Believe ZoomZoom is correct. It appears to be the primary to secondary injector transition. Hesitation varies based on throttle response. Lighter throttle it hesitates closer to 3000, moderate to heavy it hesitates closer to 3500, but never past 3500 even under full throttle.

Maybe I was not clear earlier. Here is the situation in order of events:

Got the car running, noticed hesitation and idle surging as well as surging at higher rpms. Expected nothing less from reading about these cars for the past 5 years.

Adjusted the AAS to where it is backed out 1 turn. Based this on some posts that said about surging 1100-1400rpms. Did this since it is a street ported instead of stock motor.

Idle surge reduced considerably and hesitation seems better. Some hesitation related to knock sensor being set too high. Need A/F to determine if knock is due to lean conditions.

Installed A/F gauge and noticed a lean condition at 2500-3500 rpms only under light to moderate throttle. Hooked up the J&S Safeguard A/F sensor and got the same results. Hooked both up together. Only difference was at cold start, both show lean instead of rich from cold start until about 2 minutes after start. After that, they both responded identical and responded identical to when they both were wired separately.

Checked for lean at boost, the A/F is a solid rich, so backed off the sensitivity of the knock sensor. Helped with the hesitation at moderate to full throttle (false knock readings retarding timing).

Car runs much smoother and idles good. Idle surging only at startup for about 30 seconds or less and Idles at around 800 rpm instead of 1100+

Now working on the hesitation, thought that the fuel resistor might be part of the problem. Disconnected and wired direct across to eliminate the relay. Seemed to help a little bit but not sure.

Next attempt is wiring grounding. Took a wire directly from ground to firewall grounding point, then directly inside to ECU ground bolt. Hesitation seemed much less, but still noticed the A/F going lean at 2500-3500 under light throttle and hesitation around 3000-3500rpm.

Next attempt is to bypass the O2 Sensor by disconnecting it. At the same time, hooked the signal wire to the O2 sensor (O2 is disconnected to input of stock ECU, but still hooked up to the A/F gauge).

Eliminated the Lean Condition reading at 2500-3500rpm and did not notice the 3000-3500 hesitation. Not sure if this was because I disconnected the O2 sensor while motor was running or just a fluke. Did not drive too far or too long also.

Later in the day, I went to work and on the way to work, had the 3500 hesitation again. This time with no lean conditions reading at the A/F under light throttle and only notice hesitation when under moderate or full throttle. On the way home, noticed the hesitation again and this time took notice to the A/F blip down each time the hesitation occurs. Just a split second as the hesitation occurs.

Believe it is when the transition is going from primary to secondary on the fuel injectors.

Any one do anything different than above to cure the injector transition?

Tim

Tim McCreary

When I did the auto to manual harness conversion, I installed a pigtail to plug the A/F in just before the computer. Unplugged from harness, unplugged the O2 sensor and connected the O2 to the signal wire of the A/F meter.

Rpeck

Did you ever fix this?

ljrotary

Tim, I had basically the same symptoms you are experiencing and tried everthing to resolve it. I had checked the fuel pressure, tested all solenoids and actuators related to the trubo transition, and tested the injectors. I thought it might be ignition related so I changed the plugs and.......no more hesitation!!!! My plugs had about 11K hard miles on them and when I removed them, the trailing plugs looked good and the leading plugs did have a noticable increase in the gap. My theory is that during the transition to the 2nd turbo (spike), the increased combustion chamber pressure was overcoming the higher gapped (worn) plugs and causing them to misfire. Hope this helps.

On another note, I did run a couple of highly concentrated fuel system cleaner bottles (SeaFoam)through the tank before changing the plugs. I ran 1 bottle to approx 8 gallons of gas and did it twice. I did a lot of driving above 4K to make sure the secondary injectors were firing. I did notice slightly richer A/F readings after the 1st tank and no more lean readings. It did not cure the hesition but I do feel it affected the injector flow/pattern. I have never believed in in-tank injector cleaner before and have never used it in the 135K miles of owning my car, but after seeing the results myself, I'll be using it more often. Let me know if any of this works for you......Joel