Rotary4tw

iTrader: (3)

I appear to have the 3800 rpm hesitation on my 86. At first, I thought it was a bad gas tank which was causing debre to clog the fuel filter. We replaced the tank, and we also replaced the fuel filter. We also replaced the fuel pump. This was all last year before I knew about rx7club.com.

I'm thinking it must be a grounding issue, so I'm going to attempt to reground the main points in the engine. If that fails, I'll look at the secondary injectors, they may be closed or something.

Here is the one fact that I don't understand though, and I'm not sure if it's consistent with the standard 3800 rpm hesitation.

When the car does not have a load on it (in neutral) it rev's all the way to redline cleanly and without issue. It's only when I am in gear that I face this hesitation.

Does this detail rule out the ground or injectors not working? I don't know enough about the duty cycles of the 2ndaries as to if they are even needed to get the car to redline w/o load.

Thank you in advance.

(If there are any threads that walk you through the regrounding, just let me know and I'll keep searching)

-Rotary4tw

scheistermeister

thats the way my 3800rpm hesitation has been, funny thing is sometimes it does it and sometimes not. ive added a few grounds but it hasnt changed anything. i also replace the fuel filter. sounds like the typical hesitation to me.

1RX7DRIVER

wow I am surprised no one has jumped on yall about the search button located on the top of the page or the FAQ page yall may want to use them before posting common question

Rotary4tw

iTrader: (3)

In my research about the hesitation, I was unable to read anything that talked about whether the car had this issue all the time, or only when under load.

I don't understand how a bad ground would cause the 2ndaries to not fire when the car had load, but it wouldn't happen when the car was in neutral.

Let me clarify, I'm not asking how to fix the 3800 rpm hesitation, I'm specificly asking if I can rule anything out if the car does not stumble when it is not under load.

Sorry for the confusion,

-Rotary4tw

Syonyk

I believe the secondary injectors don't come on unless the car is under load.

Disconnect the boost sensor on the passenger's side tower from the engine's vacuum. Plug the vacuum leak into the engine (though it probably won't matter for this test). Now the ECU is seeing full manifold pressure, and will bring the secondaries online as you free-rev it. Does it hang at 3800 RPM? If so, then it's definitely a problem with the secondaries, and the typical "3800 RPM hesistation".

-=Russ=-

1RX7DRIVER

my car use to have a really bad hesitation at 2900 and 5400 only when it was under a load i ran 2 new grounds one from the - battary to the body and then another one from the - battary to the block and i havent had any hesitation problems with it yet. i would say just try them it would never hurt anything just help and also regound your ecu

NZConvertible

That's correct.

The hesitation is the secondaries coming on (badly). The reason there's no hesitation when revving in neutral is because the ECU doesn't turn them on unless the AFM (or MAP sensor, not entirely sure) tells it the engine is under load.

Rotary4tw

iTrader: (3)

Thank you, this is the information that I was seeking.

You guys are the best!

I'll keep you posted on my tests and hopefully we can add another "3800 rpm hesitation" to archives...

-Rotary4tw

Toxindude

I have the same exact problem he has does that mean I have a bad boost sensor ?

dothacker

can't be a boost sensor, TPS most likely.

NZConvertible

Well the TPS has nothing to do with the secondary injector activation, and the MAP sensor does, so it's possibly a bad MAP sensor signal and unlikely to be caused by the TPS.

Check the MAP sensor as per the FSM.

My5ABaby

iTrader: (7)

This may help. Basically just read what Hailers wrote.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/pressure-sensor-ground-3500-hesitation-fix-572799/

HAILERS

Before you tear your car up, go to the vacuum line for the pressure sensor. Pull it off. Look and see if there is an ORIFICE inside the line. It should be within about a inch or two of the end that attaches to the intake manifold.

See the attached jpgs for what a ORIFICE looks like. Do a SEARCH for ORIFICE. I wrote down the Mazda part number some time ago. Or make one. Get one of those plastic vacuum pipes that connects one piece of vacuum hose to the other. In one end put some EPOXY. As the EPOXY hardens, push a sewiing needle thru the EPOXY. Make sure you put some vaseline on the needle so you can withdraw it later after the epoxy hardens. Then you can put a small length of new hose on one end of the plastic pipe and the original vacuum hose on the other end. Then install it on the engine and give it a try.

Once upon a time i replaced vacuum hose on my 87n/a. Drove the car half a block and wondered where this huge hesitation came from. Put the old line on and all was weill. Hmmm. Looked in the line and saw the ORIFICE. PUt it in the new vacuum line and all was well.

Well, it was better is what I should say. Later I found that TOTAL VICTORY was only accomplished when I went to the gnd wires at the ECU plugs and soldered a new wire to them and put a ring terminal on the other end of the new wire. That ring terminal attaches to one of the studs that hold the ECU bracket on the firewall..

My5ABaby

iTrader: (7)

Hmmm, I need one of those... The new wire fixed my hesitation mostly, but I still occasionally get a small amount.

HAILERS

I find a sewing needle of 0.025 inch, will not go thru that hole. That'S the smallest needle I have. I think I could have SHOVED it thru the hole. So that figure is a fairly close idea of how little that hole is. Like I said, make one using epoxy and a plastic vacuum hose connector or?????? Fve minute epoxy and your thru in a half hour and ready to drive.

My5ABaby

iTrader: (7)

So something like "ITW Performance Polymers (Pos) / 5 Minute Epoxy System" from Autozone?

HAILERS

Any epoxy that will set up hard is fine. While still in a peanut butter consistency, stick a sewing needle into and thru the epoxy. Vaseline on the needle. When the epoxy hardens in say ten/fifteen minutes, withdraw the needle and you should have a hole there in the epoxy.

If you have a piece of 0.020 safety wire handy that could be used instead of a needle.

Toxindude

where does the old vacuum hose hook up and the new hose hook up . Is the new hose the same size as the old one ?

Sobr609

iTrader: (2)

i had the same problem in my 87 gxl..like other people said it was the secondary injectors

NZConvertible

That's because the hole is 0.5mm or 0.020", as per the parts catalogue.

That's my experience also. I did this after cleaning up every factory ground point in the engine bay. This would indicate it was a problem with the actual wires themselves, which seems very odd to me. I wonder if it was actually the crimped junctions where all the ground wires come together that were bad. I used these as the location for connecting the new wires. Maybe they were "fixed" by soldering the extra wires on, hence making the whole joint more secure. Dunno, just a guess.

Here's some info on this I posted recently: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/ecu-ground-wire-questions-658615/

HAILERS

I used a VACUTITE plastic union like in the attached jpg. And two hose as shown in the attached jpgs. Not pretty. The real ORIFICE is the one in the earlier pictures. Black/oval with a 0.020 hole in the middle.

All I know, is, that the original car came with an orifice in the vacuum line to the boost/pressure sensor. Back to stock, says I.

Toxindude

I agree I tested the TPS today it is workin perfectly . Somthing I noticed today also if I apply a certain amount of pressure to the gas pedal not very much it will come out of the hesitation . I am kinda curious if I blew out my FPR when I had that walbro pump and way to big injectors . Is that a possibility ?

P.S Can anyone tell me where I can find new 5th/6th port air pump actuators ? I would like to replace them .

jgrts20

Convert your actuators to electric, its more reliable!!

Chris

Toxindude

Where can you find electric ones , or the stock actuators but new not used ?

micah

Does this orifice stuff only apply to S4's? I swapped out all of my vacuum lines on my S5 (including that line) and I had no such noticeable hesitation.