Cat delete now cutting out at 3500 RPM
10-19-21, 06:22 PM
#1
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Thread Starter
Cat delete now cutting out at 3500 RPM
Hi - I have a 1988 10th AE rx7 with 67k miles. Had it serviced in FL before moving it to Washington state.
cat was deleted and midpipe/down pipe put in.
now in the cooler weather in Washington when I step on the gas hard it boggs down at 3500 rpms. The FL racing shop says it needs a fuel cut defensor. I’m not mechanically inclined but wanted to ask you guys before taking it somewhere.
thanks!
cat was deleted and midpipe/down pipe put in.
now in the cooler weather in Washington when I step on the gas hard it boggs down at 3500 rpms. The FL racing shop says it needs a fuel cut defensor. I’m not mechanically inclined but wanted to ask you guys before taking it somewhere.
thanks!
10-20-21, 11:54 AM
#2
Hi - I have a 1988 10th AE rx7 with 67k miles. Had it serviced in FL before moving it to Washington state.
cat was deleted and midpipe/down pipe put in.
now in the cooler weather in Washington when I step on the gas hard it boggs down at 3500 rpms. The FL racing shop says it needs a fuel cut defensor. I’m not mechanically inclined but wanted to ask you guys before taking it somewhere.
thanks!
cat was deleted and midpipe/down pipe put in.
now in the cooler weather in Washington when I step on the gas hard it boggs down at 3500 rpms. The FL racing shop says it needs a fuel cut defensor. I’m not mechanically inclined but wanted to ask you guys before taking it somewhere.
thanks!
10-20-21, 02:40 PM
#3
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possible fix for you
i just bought my 87 fc (GXL) it is an NA, and when my dad and i were driving it home, it would consistintly flatten out around 3500-4500, the only way i was able to get it to rev higer was to put the pedal all the way down. now, mind you, the gxl is a 6 port 13b, wich means it has what is basically rotary vtech. BUT HERES THE CATCH!!!! in the 87 it is actuated through exhaust pressue, kind of like a blow off valve, (it looks like one too). because i could only open the actuator with the pedal to the floor, i realized that it must be a issue with back pressure, the other day i had it inspected as to register it for my state, and there was a massive exhaust leak. mine is in the shop right now getting an HKS exhaust fitted to fix the issue
my advice would be to check backpressure in the exhaust, and compression in the engine. idk, just my two cents
my advice would be to check backpressure in the exhaust, and compression in the engine. idk, just my two cents
10-20-21, 02:49 PM
#4
The question is what is your boost pressure when it bogs/cuts out. I don’t remember what boost pressure the stock fuel cut occurs at but look it up and see if that would solve your problem.
but with less restriction in the exhaust, it’s probable you’re boosting more than stock so a fcd is recommended anyways.
but with less restriction in the exhaust, it’s probable you’re boosting more than stock so a fcd is recommended anyways.
10-20-21, 05:55 PM
#6
You're going down a road many went down years and years ago. The engine is overboosting due to not enough restriction in the exhaust (for a stock car). This doesn't just happen on an old Rx-7. If you get a newer turbo car and go catless you will fuel cut too unless it is tuned. That means the engine computer needs to be reprogrammed to handle the changes in the exhaust system. It's pretty straightforward if you have a 4 cylinder turbo Mustang or a Subaru or whatever. On an old Turbo II the options are not so easy anymore. The one "drop in" reprogrammed chip ECU was an Rtek, and those have been out of production for a long time.
I know Florida is pretty "meh whatever" about cat deletes, but it is a risky modification for an engine. You need to make a road map for what you want the car to do. Do you want to keep it mostly stock, especially considering the increasing value of these cars? In that case you need to put a cat back in.
If you put a fuel cut defender in now you have to make sure the engine isn't running lean. You're opening a can of worms. You will have to consider the fuel pump, the fuel injectors, the wastegate, intake, and other sources of things that could make your engine blow up. Since you said you are not mechanically inclined, my advices is to tread lightly here or you will be just another guy who blew up an Rx-7 because he didn't realize what he was doing.
They call it a "fuel cut defender" but that's really marketing. The fuel cut IS a defender - it defends your engine from overboosting and blowing up. Removing that failsafe increases the chance of engine damage. If I go change the exhaust system on my Mustang, the ECU is reprogrammed to adjust the overboost fuelcut but it doesn't completely eliminate it. Instead it is raised to a higher pressure level, and the ECU will get a check engine light if it overboosts. An 80s Rx-7 isn't smart enough to do that, hence the many dead Turbo II's over the years with just a fuel cut defender and an old fuel pump causing a lean condition.
I know Florida is pretty "meh whatever" about cat deletes, but it is a risky modification for an engine. You need to make a road map for what you want the car to do. Do you want to keep it mostly stock, especially considering the increasing value of these cars? In that case you need to put a cat back in.
If you put a fuel cut defender in now you have to make sure the engine isn't running lean. You're opening a can of worms. You will have to consider the fuel pump, the fuel injectors, the wastegate, intake, and other sources of things that could make your engine blow up. Since you said you are not mechanically inclined, my advices is to tread lightly here or you will be just another guy who blew up an Rx-7 because he didn't realize what he was doing.
They call it a "fuel cut defender" but that's really marketing. The fuel cut IS a defender - it defends your engine from overboosting and blowing up. Removing that failsafe increases the chance of engine damage. If I go change the exhaust system on my Mustang, the ECU is reprogrammed to adjust the overboost fuelcut but it doesn't completely eliminate it. Instead it is raised to a higher pressure level, and the ECU will get a check engine light if it overboosts. An 80s Rx-7 isn't smart enough to do that, hence the many dead Turbo II's over the years with just a fuel cut defender and an old fuel pump causing a lean condition.
Last edited by arghx; 10-20-21 at 06:01 PM.
10-20-21, 06:58 PM
#7
Full Member
You're going down a road many went down years and years ago. The engine is overboosting due to not enough restriction in the exhaust (for a stock car). This doesn't just happen on an old Rx-7. If you get a newer turbo car and go catless you will fuel cut too unless it is tuned. That means the engine computer needs to be reprogrammed to handle the changes in the exhaust system. It's pretty straightforward if you have a 4 cylinder turbo Mustang or a Subaru or whatever. On an old Turbo II the options are not so easy anymore. The one "drop in" reprogrammed chip ECU was an Rtek, and those have been out of production for a long time.
I know Florida is pretty "meh whatever" about cat deletes, but it is a risky modification for an engine. You need to make a road map for what you want the car to do. Do you want to keep it mostly stock, especially considering the increasing value of these cars? In that case you need to put a cat back in.
If you put a fuel cut defender in now you have to make sure the engine isn't running lean. You're opening a can of worms. You will have to consider the fuel pump, the fuel injectors, the wastegate, intake, and other sources of things that could make your engine blow up. Since you said you are not mechanically inclined, my advices is to tread lightly here or you will be just another guy who blew up an Rx-7 because he didn't realize what he was doing.
They call it a "fuel cut defender" but that's really marketing. The fuel cut IS a defender - it defends your engine from overboosting and blowing up. Removing that failsafe increases the chance of engine damage. If I go change the exhaust system on my Mustang, the ECU is reprogrammed to adjust the overboost fuelcut but it doesn't completely eliminate it. Instead it is raised to a higher pressure level, and the ECU will get a check engine light if it overboosts. An 80s Rx-7 isn't smart enough to do that, hence the many dead Turbo II's over the years with just a fuel cut defender and an old fuel pump causing a lean condition.
I know Florida is pretty "meh whatever" about cat deletes, but it is a risky modification for an engine. You need to make a road map for what you want the car to do. Do you want to keep it mostly stock, especially considering the increasing value of these cars? In that case you need to put a cat back in.
If you put a fuel cut defender in now you have to make sure the engine isn't running lean. You're opening a can of worms. You will have to consider the fuel pump, the fuel injectors, the wastegate, intake, and other sources of things that could make your engine blow up. Since you said you are not mechanically inclined, my advices is to tread lightly here or you will be just another guy who blew up an Rx-7 because he didn't realize what he was doing.
They call it a "fuel cut defender" but that's really marketing. The fuel cut IS a defender - it defends your engine from overboosting and blowing up. Removing that failsafe increases the chance of engine damage. If I go change the exhaust system on my Mustang, the ECU is reprogrammed to adjust the overboost fuelcut but it doesn't completely eliminate it. Instead it is raised to a higher pressure level, and the ECU will get a check engine light if it overboosts. An 80s Rx-7 isn't smart enough to do that, hence the many dead Turbo II's over the years with just a fuel cut defender and an old fuel pump causing a lean condition.
Let us know what you end up doing.
Last edited by rotary_fan; 10-20-21 at 07:04 PM.
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10-21-21, 01:19 PM
#8
Junior Member
Thread Starter
OP here - My desire is to keep it as close to stock as possible. It sounds like it makes more sense to put a new cat on there and then see if it runs smooth again.
Yes - basically when i floor the accelerator the car just bogs down (doesn't stall) and won't go higher than 3500 RPM.
I'd be happy to have a new cat put in and sounds like this is the way to go over the FCD. Do you all think this will fix that problem?
Yes - basically when i floor the accelerator the car just bogs down (doesn't stall) and won't go higher than 3500 RPM.
I'd be happy to have a new cat put in and sounds like this is the way to go over the FCD. Do you all think this will fix that problem?
10-22-21, 09:11 AM
#9
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i belive it may, im no expert, but i have a similar issue and its being fixed as we speak,
i agree with the others above, but as my fc is naturally aspirated i cant speak to the turbo function, does yours have a turbo?, becasue that is really the only difference in the responses, as mine only applies to the N/A engines. when i bought mine the exhaust leak was there, and it faild inspection, with new exhaust the problem is gone, turbo would make more pressure in the exhaust, so that issue would not be as noticible for turbo models, the N/A actuators for the 2nd ports will not work well without a good exhaust. when i get home i will post some pictures of the service manual that proves this.
i agree with the others above, but as my fc is naturally aspirated i cant speak to the turbo function, does yours have a turbo?, becasue that is really the only difference in the responses, as mine only applies to the N/A engines. when i bought mine the exhaust leak was there, and it faild inspection, with new exhaust the problem is gone, turbo would make more pressure in the exhaust, so that issue would not be as noticible for turbo models, the N/A actuators for the 2nd ports will not work well without a good exhaust. when i get home i will post some pictures of the service manual that proves this.
10-22-21, 10:17 AM
#10
Rotary Freak
i belive it may, im no expert, but i have a similar issue and its being fixed as we speak,
i agree with the others above, but as my fc is naturally aspirated i cant speak to the turbo function, does yours have a turbo?, becasue that is really the only difference in the responses, as mine only applies to the N/A engines. when i bought mine the exhaust leak was there, and it faild inspection, with new exhaust the problem is gone, turbo would make more pressure in the exhaust, so that issue would not be as noticible for turbo models, the N/A actuators for the 2nd ports will not work well without a good exhaust. when i get home i will post some pictures of the service manual that proves this.
i agree with the others above, but as my fc is naturally aspirated i cant speak to the turbo function, does yours have a turbo?, becasue that is really the only difference in the responses, as mine only applies to the N/A engines. when i bought mine the exhaust leak was there, and it faild inspection, with new exhaust the problem is gone, turbo would make more pressure in the exhaust, so that issue would not be as noticible for turbo models, the N/A actuators for the 2nd ports will not work well without a good exhaust. when i get home i will post some pictures of the service manual that proves this.
Your engine is NA, so you do have aux ports. In your case the back pressure isn't detected by the ECU at all, it's purely mechanical. The little valves that open the aux ports only work from exhaust back pressure. No pressure, no aux port functionality, car runs out of steam at 4k or so.
The issues are unrelated between the two cars, but since it's a similar symptom at a similar rpm range it's not unusual to think they are related.
The cure for both is a catalytic converter. There are other options to solve both issues but a cat is the simplest of them assuming you want a stock-ish car.
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