redstreak

HAHHAHAHA! Well with the help of two of the most knowledgable RX-7 Mechanics I know in just 2 short hours we fixed my six ports and my 3800 hesitation.

After trying numerous things to fix the hesitation I went to get some help, and I don't know if this aplies to the series 5 cars but under the air box there is a little metal box bolted to the fender. This "box" if I understand correctly is what receives the signal from the ECU and then tells the injectors to come on. It controls both the primary and secondary injectors, not sure what causes it to go bad or why it seems to only affect the secondaries, but WHO CARES!! WOHOOO now she pulls all the way to redline. I love my RX-7, sex? who needs it at least the red head in the garage doesn't complain when I want to give her a lil'. lol

RETed

You could at least tell us what MODEL you've got.&nbsp It sounds like it's an '86 or an early '87 model which has the fuel injectors resistor block up front.&nbsp Any of the later FC's do NOT have this block, and your solution is of no help to them...



-Ted

EcuXavi

Hey redstreak, the metal box under the air box did you replace it or ground it some how?
If you grounded please tell me how did you do it??

redstreak

Ok sorry, in my excitment I left out a fair ammount of detail. I have an '86 RX-7 and I have had the hesitation for as long as I have owned the car. I finally got fed up and began my search to fix it.

The first thing I did was I got my injectors cleaned, I noticed a little more power in the low end but it didn't fix anything. The seccond thing I did was install a new fuel filter, again nothing. Then I had done a little research and figured out that my seccondary injectors were definately not comming online. This is where it gets a little strange. I happened to come across this forum and did a little reading. There are people who have fixed their hesitation by grounding everything but that didn't make a whole lot of sense to me becuase the only way I can see this making a difference is if there is really high resistance at one point in the circut and by grounding the **** out of everything you manage to create enough voltage at one end to overcome the resistance and still provide enough voltage to send a signal (one guy mentioned wiring in a capacitor). So I probed around with the help of a mechanic here in Winnipeg and he began to tell me about a (not really sure how to describe but I'll call it a resistor) under the air box. I unbolted the air box and he measured the resistance across the terminals that send the signal to the secondaries, sure enough it was bad. We replaced it with one he had kicking around and BOOM hesitation gone. Getting this part from Mazda will be a LOT. Find a good one at a junk yard.

execelon1

can you tell us the name or part #

SoulPyr0

yeah, no kidding i want to know how to fix that i only have it sometimes tho... i have a 91 Vert... it's weird but, only sometimes it does it...!?!?!

RX7BEAR

is this that little aluminu, 4inch by 2 inch thing with a big plug on it . and it says denzo on it?

HAILERS

That thing is the solenoid resistor on a 86 to 87 and 1/2. It receives a solid 12v and this 12v goes to four resistors in the unit and from there to the injectors. This 12v does not switch on and off. Its steady. The switching of the injector pulse is on the ground wire of the injector and is done by the ECU. Here's a jpg of the manual check of the resistors:

HAILERS

Here's a simplified schematic of the solenoid resistors:

RX7BEAR

wow I will have to check that late on when I get done with my jobs today . thanks Hailers !!!!! So do you think maybe alot of our 3800 rpm probs are from this ?

Snrub

iTrader: (1)

Christ Hailers, do you have every page of the manual scanned in?

HAILERS

Cheers for REDSTREAK and friends. I never considered the solenoid resistor pack in the past except for ohming out the wiring for the injectors. Shoulda though. I'd be interested if REDSTREAK ohm'd out the resistors to the diagram in the above post and tell us what went wrong with the resistors. Only good fix for the 86-87 and a half cars though. Other cars might ohm out the wiring for shorts and opens while manipulating the harness and plugs.

redstreak

Woa, a lot of posts since the last time I checked.

Hailers, yes the Solenoid Resistor is what I replaced, I will look to see if I can find my old one and test the resistance across it and the one that I put in place of it. I will keep you guys posted, I am happy to do anything I can to help out another rex owner.

2ndGen.rocket

how easy was it to replace it? All you did was replace that little resistor box? I know I have taken the thing out before to polish it, but is it as simple as unplugging it and plugging a new one in? Also, do you have to reset the ECU?

2ndGen.rocket

And if we go get one out of a junkyard, what are the chances that that one will be bad too? I don't know of any way to test them out

redstreak

2ndGen.rocket- yup it's that easy and no you don't have to reset the ECU. The chances that one will be bad from a wrecker is 50/50. To test it you will need an multimeter to find the resistance across the terminals. Give me a little bit of time to check what the resistance should be. Unless Hailers has it in that massive online catalog of his. hehe lol.

rxse7en

I just ran the FSM test for the solenoid and came up with 6.1ohm across the terminals. Should be between 5 and 7ohm. I've already regrounded the ECU, the injector harness, the block, the boost sensor and the battery and still get the high-rpm stumble randomly. For instance, for the last three days no hesitation. Today, after replacing the front diff mount I got the hesitation every time I got up around 5k rpm. This evening, I reset the idle, timing, and TPS took the car out again and now no hesitation. I'm sure it'll be back again. The only thing I haven't tried is another ECU and testing the secondary injectors. At least I know I've checked almost all systems and I'm systematically covering all bases. I was hoping my solenoid was blatantly bad, alas, I'm left with no reason for the hesitation.

I'll check the injectors next.

Keep is informed on what you find with your solenoid.

B

redstreak

Well this is different from the problem I was encountering. My hesitation was at 3800 on the dot and I could not go past this point, period. It was like hitting a brick wall, yours could be something like a clogged injector. Have you had them cleaned?

2ndGen.rocket

yeah my problem is right at 3800, but it isnt so bad that the car stumbles and doesnt want to go. It is just a slight little jump that is does and keeps going. It's more annoying than anything, mainly because it doesnt do it all the time. Only once in a while, like when I am trying to race someone or something.......

StarionX

rxse7en, the problem you're having is different to the 3800 RPM hesitation that is very common (and trust me, once you get this, it's ALWAYS there until you fix it). In fact, I've just gotten the problem a few days ago... grrrrrrrrr

I'd say you'll need to look further for a resolution.

rxse7en

Well, I'll test the injectors shortly and see if I have any problems there. I'm off to Dizzy World with the family Saturday, so I may get a look at them on Sunday and update this thread.

B

rxse7en

PS. I "snuck" the car out all day today, lots of redline runs and no hesitation. I'm gonna start thinking it's a short in the harness which is very likely. The previous owner had the Mazda rebuilt installed 20k miles ago and you can see where the mech spliced the harness in the engine bay. Oh the joy of hunting down a hort in that mess.

Brian

St. Louis Racer X

I just bought an 86 Rx7 NA, and its been nothing but problems, out of the two months i've had it is only been running about 3 and 1/2 weeks i finally got it to pass emissions and got all the other little problems fixed and then just like 3 days ago i got in and started driving and the car just would not break 4000 rpm's it had sometimes studdered at 4000 but it would always push through in a couple of seconds dose anyone have any ideas about this do you think it's the solenoid, you guys were talking about or do you think it's injector realted, i know it's not the fuel filter cuz i just changed that. any suggestions

redstreak

well your seccondary injectors are not comming online. Test the resistance across each of the injectors, the resistance range can be found in a Hayne's manual. If they are good then test the resistor that I have mentioned above.

silverrotor

iTrader: (1)

Can anyone address the hesitation to the 1987.5 and on, more particulairly an 88 GXL. We don't have the solenoid as the previous 2nd gens have. I have re-grounded my ECU, TB and the engine! Although, now the hesitation does not kick in as much I have calmed It down abit. I have also noticed that in colder weather the hest. becomes increasingly violent. Any suggestions to eliminate the notorious 3800rpm hesitation to the 87.5 and beyond RX-7's?