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Old 07-22-07, 10:00 PM   #1
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3800 RPM hesitation...backfires

I have a 91 vert and am getting severe hesitation at 3800 rpm. After reading through threads all weekend I am seeing very similar issues from other folks having 3800 rpm issues. I have looked over the major grounds and the connections look solid but I have not replaced the cables. I also have removed my cat converter to see if this was causing the problem...i bielieve the cat was bad anyway because it was smoking really bad and now its not.

The engine is also popping real bad along with backfiring. Im also having a hard time starting when its cold. I have read that i need to check ports 5/6 and clean my injectors. Because I am new to the rx7 and am not the best mechanic in the world, getting to the injectors looks kinda tricky. Also, i think my timing might be off but i dont have a timing gun to check.

I am hoping that someone can give me some ideas behind the popping/backfiring and maybe the best place to start with the 3800 hesitation. Can the timing being off cause the hesitation and backfiring?

Any ideas or direction would be most appreciated.

Thanks,

--Marc
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Old 07-22-07, 10:08 PM   #2
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Backfiring usually means its runnin' too rich and the hesitation at 3800 rpm's is more then likely the actautors that run ur 5th and 6th ports(which open at 3800). Do a search on 3800 hesitation, this has been covered plenty!! Since ur new start here: http://www.rx7club.com/search.php?searchid=3688202 You can always go electric on the ports!!

Chris
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Old 07-22-07, 10:17 PM   #3
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Thanks Chris...not to be completely ignorant but what are the main causes of a rotary engine runnin too rich?

Thanks for the feedback,

--Marc
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Old 07-22-07, 10:21 PM   #4
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Could be a number of things, change of weather temp!! have you change anything on the car or done any work to it lately? Ive heard even a tune up could make it run a little rich, but I havent seen that!! search "running rich" or wait for other responses.

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Old 07-22-07, 10:52 PM   #5
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Poor ECU grounds will cause a rich condition at 3800 rpm and cause hesitation. Usually a series four problem. Try regrounding the ECU ground wires to the bracket that holds the ECU in place. In other words try (just a suggestion) a new wire to the ECU ground wires and terminate that wire on a stud that holds the ECU bracket in place. Which wires on the ECU plugs are ground. See the FSM, FUEL SECTION, CONTROL UNIT. It states which wires on the plugs are GND wires.

This is only a suggestion. DO NOT get silly and gnd the chassis of the ECU. That is ....silly. The WIRES in the plugs that are gnd wires are what I speak of.

I'm a TRUE BELIEVER in this fix. Worked on two of my cars for 3800rpm hesitation (injector transition is what caused it , not aux actuators coming online). At 3800rpm if there is a load on the engine, then the primary injectos fall to half of the duty cycle they were at at 3800, and at the same instant the secondary injectors come online to compliment the primay injectors.

Gotta watch TRUE BELIEVERS though. They'll lead you over a cliff if you don't watch out. humor.
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Old 07-22-07, 11:00 PM   #6
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I haven't done anything to it lately...its actually been sitting for a while...maybe driven once a month if lucky. I just pulled a couple of plugs and they have black tips....one had a little oil/moisture on it. Not exactly sure what that means in a rotary?? Any thoughts?

Thanks for the help,

--Marc
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Old 07-22-07, 11:25 PM   #7
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Thanks Hailers. I will get a new ground for the ecu asap. I never would of thought that grounds can cause such hellish issues. I will take a look the ecu diagram and make sure i dont have any questions on the ground wires.

Thanks for the feedback!

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Old 07-23-07, 02:31 AM   #8
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Quote:
Originally Posted by jgrts20 View Post
...the hesitation at 3800 rpm's is more then likely the actautors that run ur 5th and 6th ports(which open at 3800).
This info is completely wrong and should be ignored. 6PI issues don't cause the 3800rpm hesitation, or any other hesitation.

Something not mentioned yet is the secondary injectors. If the problem only occurs AT 3800rpm but the engine accelerates fine above that then it's probably a grounding issue. If the problem occurs ABOVE 3800rpm then it could be a problem with the secondary injectors themselves, most likely a poor electrical connection. The secondary injectors' connectors are easily accessed, and should be inspected to make sure they're thoroughly clean inside (the injector too) and securely clipped on. If the connectors are broken or cracked they should be replaced.
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Old 07-23-07, 08:36 AM   #9
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This info is completely wrong and should be ignored. 6PI issues don't cause the 3800rpm hesitation, or any other hesitation.

Something not mentioned yet is the secondary injectors. If the problem only occurs AT 3800rpm but the engine accelerates fine above that then it's probably a grounding issue. If the problem occurs ABOVE 3800rpm then it could be a problem with the secondary injectors themselves, most likely a poor electrical connection. The secondary injectors' connectors are easily accessed, and should be inspected to make sure they're thoroughly clean inside (the injector too) and securely clipped on. If the connectors are broken or cracked they should be replaced.
The fuel injectors is a good part in the 3800 issue and ground, you are correct there!! My issue when I had the 3800 problem was my actuators werent opening. I just figure he should check them before screwing with the injectors cause those my friend are a pain(especially when your new).

Chris
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Old 07-23-07, 09:05 AM   #10
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Quote:
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The fuel injectors is a good part in the 3800 issue and ground, you are correct there!! My issue when I had the 3800 problem was my actuators werent opening. I just figure he should check them before screwing with the injectors cause those my friend are a pain(especially when your new).

Chris
No, it wasn't. How would them not opening cause a hesitation?
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Old 07-29-07, 02:39 PM   #11
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I have a 88 rx7 that has a severe problem accelerating over 3000/4000 rpm, It will stay in this range and hunt not gaining any more rpm. When your driving the car it will jerk the crap out of your neck when it hits that 3000/4000 rpm range.
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Old 07-29-07, 06:02 PM   #12
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could the port actuators flutter because of inconsistent back pressure, and cause a changing pressure zone in the intake that causes a feeling like the motor is hesitating?
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Old 07-29-07, 10:28 PM   #13
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Not much of an update....New Problem!!!

I've been out of town and haven't had a chance to try new ground wires. I think I may have a more serious problem though. When I started digging into these issues a while back I had been having a problem with the car overheating. I replaced the thermostat and it quit but I think I may have overheated the engine in the process. I just started the car up and removed the radiator cap and the coolant does bubble. I am not a happy camper right now to say the least. Besides testing the compression does anyone know other ways to confirm that the o-rings are bad? The car had smoked really bad so I took off the cat conv and the smoke has stopped.

Any thoughts/advice?

Thanks,

--Marc
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Old 07-30-07, 01:47 AM   #14
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Quote:
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I have a 88 rx7 that has a severe problem accelerating over 3000/4000 rpm, It will stay in this range and hunt not gaining any more rpm. When your driving the car it will jerk the crap out of your neck when it hits that 3000/4000 rpm range.
Go back and read post #8.

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could the port actuators flutter because of inconsistent back pressure, and cause a changing pressure zone in the intake that causes a feeling like the motor is hesitating?
No.
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Old 07-30-07, 02:15 AM   #15
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Quote:
Originally Posted by Austin91rx7 View Post
I just pulled a couple of plugs and they have black tips....one had a little oil/moisture on it. Not exactly sure what that means in a rotary?? Any thoughts?

Thanks for the help,

--Marc
Oil/moisture on spark plugs is a indication of flooding. Search de-flood.
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Old 07-30-07, 08:28 PM   #16
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Moment of truth....O-rings

OK, I just went out and filled the radiator with coolant and started the engine with the cap off. The coolant has a steady bubble when the car is running. When I hit the throttle the coolant is sucked down into the radiator and then comes back up and spills over.

Is it safe to say that I overheated the car and the o-rings are bad? If this is the case I have absolutely no idea what the car would be worth now.

Total bummer as it was probably ignorance that overheated the engine in the first place.

Any feedback would be most appreciated.

--Marc
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Old 07-30-07, 08:51 PM   #17
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If you overheated your car you would have seen steam coming out of the engine bay first, and you'd be missing a lot of coolant. But I dunno, maybe your coolant seals were already bad before that. The bubbling should stop or get really slow over time (maybe 1 bubble every several seconds), besides that I'm not sure how to test. Hopefully someone will post a better answer.
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Old 07-30-07, 10:03 PM   #18
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for the backfiring, it is possible you have a small exhaust leak or vacuum leak
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Old 07-31-07, 11:09 AM   #19
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Thanks Guys! Coolant in the engine?

Unfortunately I have seen some steam coming from the engine at one point. Everytime it overheated I was pretty sure that I had turned the engine off in time...I never saw the needle max out. After reading some additional threads it looks like the rotaries dont take much though.

Any additional advice on how to verify that coolant is indeed going into the engine would be helpful.

Does anyone have an idea of what the car would be worth with needing a new engine. Unfortunately I dont have the time or the tools to rebuild.

Thank you,

--Marc
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Old 08-01-07, 12:13 AM   #20
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Question ?

Quote:
Originally Posted by HAILERS View Post
Poor ECU grounds will cause a rich condition at 3800 rpm and cause hesitation. Usually a series four problem. Try regrounding the ECU ground wires to the bracket that holds the ECU in place. In other words try (just a suggestion) a new wire to the ECU ground wires and terminate that wire on a stud that holds the ECU bracket in place. Which wires on the ECU plugs are ground. See the FSM, FUEL SECTION, CONTROL UNIT. It states which wires on the plugs are GND wires.

This is only a suggestion. DO NOT get silly and gnd the chassis of the ECU. That is ....silly. The WIRES in the plugs that are gnd wires are what I speak of.

I'm a TRUE BELIEVER in this fix. Worked on two of my cars for 3800rpm hesitation (injector transition is what caused it , not aux actuators coming online). At 3800rpm if there is a load on the engine, then the primary injectos fall to half of the duty cycle they were at at 3800, and at the same instant the secondary injectors come online to compliment the primay injectors.

Gotta watch TRUE BELIEVERS though. They'll lead you over a cliff if you don't watch out. humor.
Are you saying to take the three smaller ground wires and instead of recrimping them or soldering them to ground those three wires to the ECU bracket ? Do you have a pic of how this is done I guess I am not quit getting the picture .
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Old 08-02-07, 04:57 AM   #21
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Quote:
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Are you saying to take the three smaller ground wires and instead of recrimping them or soldering them to ground those three wires to the ECU bracket ? Do you have a pic of how this is done I guess I am not quit getting the picture .
word...
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Old 08-02-07, 11:02 AM   #22
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word...
Try again:
Instead of the above, try this more standard reground of the ECU gnd wires. Follow all three wires up the harness. They all come together about six inches up the harness. Solder a new wire to those that exist. Ground the other end of the new wire to the bracket that holds the ECU in place or any other chassis ground point near by that is clean and corrosion free.

My first post suggested removing each gnd wire one at a time. Then soldering a new wire to the terminal that goes into the ECU plug. Just solder it to the shank of the terminal where it won't interfere with the reinstallation of the terminal into the ECU plug. A single strand piece of wire in the 18-22 gauge works better than multi strand wire. The other end of the new wire gets a ring terminal and bolted to the ECU bracket. You do this with all three/four wires.

The original gnd wire stays in place. It just has a new wire soldered to its shank.

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Old 08-05-07, 09:11 PM   #23
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http://www.aaroncake.net/rx-7/grounding.htm
You will need: contact cleaner, stainless bolts, dielectric grease, some method of sanding/filing/wire-brushing. Wire is not the issue. It's the end connections and finding out which components to ground. Aaroncake advocates fixing the stock grounds instead of attaching grounds to random places (which doesn't do anything anyway). IMO - as long as you ground the same components as the stock grounds - taking a different wiring route might be easier than trying to access some of the stock grounds.
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Old 08-06-07, 12:16 PM   #24
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My wires dont come together I looked up the harness more than six inches . They seem to stay seperated from one another .
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Old 08-06-07, 12:49 PM   #25
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Quote:
Originally Posted by Austin91rx7 View Post
OK, I just went out and filled the radiator with coolant and started the engine with the cap off. The coolant has a steady bubble when the car is running. When I hit the throttle the coolant is sucked down into the radiator and then comes back up and spills over.

Is it safe to say that I overheated the car and the o-rings are bad? If this is the case I have absolutely no idea what the car would be worth now.

Total bummer as it was probably ignorance that overheated the engine in the first place.

Any feedback would be most appreciated.

--Marc
When you increase throttle the coolant will suck down because the water pump is sucking harder it will then overflow when you let off, that is normal, let the engine warm up then the thermostat will open, then the engine will fill with the fluid, then you can fill the radiator completly up, only then is your car completly full of fluid, at that point you shouldn't open your cap because it will leak, when filling you can even have someone hold the throttle down a little to suck the fluid down and you can fill up, replace the cap before they let off the pedal though, that is usually what i do when I fill my radiator to ensure there is enouch fluid, any excess will push into the overflow bottle, just make sure that isn't to full and you should be good.
Now I am new to rx7's but this is just general automotive here, the way I have filled every other radiator in the past.

If you do have an oring problem I would assume you would smell the antifreeze burning, it would be a very strong sweet smell.

i
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Old 08-06-07, 12:49 PM
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