yearrgh

I'm helping a friend get the 87 he just bought running. It's having issues idling and on deceleration. If you bleep the throttle at idle, it will rev normally then stall, but its fine if you slowly let the gas back out. It also seems to have a massive version of the 3800 rpm hesitation. At 3800 and upwards it starts hesitating, it almost feels like fuel cut in my turbo, but as the title says, it's n/a. This only happens if the throttle is more than halfway open. We tried adding grounds, which helped, but didn't fix the problems. My first hunch turned out wrong, so does anyone have any ideas? Could a vacume leak somewhere have an effect on the secondaries?

Cosmo Donk

Yah, vacuum leaks suck but I dunno if that is the problem. Check for leaks anyway though. Also, clean out the TB and make sure the throttle plates are all working good and smooth, especially the secondaries because those like to stick. They are the ones attached to the Thermowax.

Also, if it dies when you let out the gas fast the TB probably needs adjusting. There are 2 main adjustments. The throttle stop set screw, a very small screw that stops the plates from closing too far, and then there is the throttle PLATE adjustment screw. This one will open and close the primary plate. Sometimes if the set screw is too far backed out the throttle PLATE screw will be the one stopping things and when you let off the gas real fast the plate will close more than it is supposed to. You can try closing the plate more and then using the set screw to set the idle.

yearrgh

Thanks, sounds good for that problem. Does anyone have any ideas about the issues over 3800 rpms? Why would it pull normally all the way to redline if the throttle is less than half open, but bog immediatly if you push it farther at any rpms over 3800? It revs normally if you do it in neutral. Do the secondaries only come on under load with the throttle open past a certain point, or do they always turn on at 3800? If they only come on if the throttle is open past a certain point, then the problem is that his secondaries aren't firing at all. If not, then i'm really confused.

yearrgh

Of course searching finally turned up something useful immediatly after posting that. It's definatly the secondaries not firing at all. If I recall correctly, my 90 TII injectors that are currently sitting in a bag would not work on his 87 n/a for us to test? The harness, at least around the plugs, looks like its in great shape. I need to talk to Andrew and find out if the problem happened suddenly to him or was troubling the previous owner. He and his dad have been reconditioning the car, so it's been sitting for awhile, but I don't think it's been sitting long enough to cause trouble. Anyhow, we can run through the fuel injector check in the manuel, but if anyone has any thoughts I'd be glad to hear them.

Cosmo Donk

Does it ever work well when you floor it up at 6000 or so when driving? I am wondering if the secondaries are sticking. If it works okay way up there then they are probably sticking and the high RPMS are using the extra fuel. If it doesn't work up there maybe they aren't opening at all.

Did you ground it with some UBER grounds? Like a big fatty from the engine to a clean bare metal sopt on the chassis? Then a good ground from the injectors to the engine? And then a good ground from the ECU to the chassis?

gergrx7

just do take out the senondaries

HAILERS

90 injectors won't work in a 86. Check the resistance of the secondary injectors. Should be approx 2.2 ohms. 90 injectors are approx 13ohms. NOT good for a 86 ECU. Whacks the ECU after sometime(WAG).

Make sure the pressure sensor has a orifice in it. Sometimes called a *pill*. It's an orifice. Part # somewhere on this site.

Disconnect the vacuum hose from the pressure sensor. Plug that vac line. Go drive the car. Did it hesitate under hard acceleration? Above 3500???? No? Orifice or pill missing. Note: with the vac hose plugged, the secondary injectors will come on at 3500 with or without a load being put on the engine. Slight contradiction to the next paragraph.

Secondaries only come on line over 3500 rpm AND a LOAD being put on the engine. IF the car accelerates smoothly to six grand by using a light pedal depression......then suspect bad/irregular grounds for the ECU and/or the orifice missing.

ECU grounds located under the dynamic chamber/throttle body. OR additional ones added at the mechanical splice located approx a half foot from the three ECU plugs. See the post from RXSTER at the other site.

HAILERS

Also check and see if the secondary injector plugs have been replaced and if so.......make sure the splices are any good. Put a meter lead on the injector plug and the other meters lead on a good ground, then turn the key to ON. One of the injector sockets should have 12v on it. Now twist and turn the injectors wires, especially at the splice if it exists. If the voltage comes and goes then the splice is corrupt/bad/ng. While there. put the meter on ohms and put one lead on one injector pin and the meters other lead on the other pin on the injector. Should read approx 2.2 ohms for a 86 and early 87.

gergrx7

oops o damn its early and i wasnt really reading good i just saw secondaries and was think of the tb but now i just read it well and i sound very dumb sry ignore my post i thought u were talking aboiut the TB sorry

HAILERS

OH! I actually just now read the thread. Sooooo....just how do you know the secondaries are not firing/ squirting/flowing/ whatever??????

Do this if not sure. Tap into the secondary injector wires at the ECU (they call them wire taps at RadioShack). Plug the pressure sensor vacuum hose, at the pressure sensor as described above. Monitor the voltage. It should show battery voltage until you accelerate to above 3500 rpm, then the voltage should drop. If the voltage drops....the injectors are firing/squirting/flowing/whatever/ most probably.

yearrgh

You mean it's in the vac line leading to the pressure sensor, right?

Thanks everyone, now we've got some things to check. One question though, if it's a late '87, didn't the injectors change, or was that in '88?

yearrgh

I'm pretty sure they're not firing, from the research i've done. Under conditions that the secondaries should be firing, the car falls on its *** and feels fuel starved.

HAILERS

Should be flowing when: The car is being driven under hard acceleration AND the rpm are over 3500 rpm.

The exception is: The vac hose to the pressure sensor is taken off and plugged. THEN the things flow just sitting in the driveway and reving over .......3500 rpm. The FSM claims, that with unusually good hearing .....under the above condition.... you can hear the injectors clicking. I obviously can't hear for flip. If you are also hearing deprived.....put a wire tap on one of the secondary injectors wires and monitor the voltage drop as the car is reved over 3599 rpm with the pressure sensors vacuum line blocked/plugged. It's in the FSM..sorta. FUEL SECTION. ONLINE. HTTP://WWW.ILUVMYRX7.COM free.

yearrgh

Sounds good, I'll try the screwdriver to ear trick to listen, if that doesn't work we can try what you said. Thanks again, I'll post an update after we try it.

HAILERS

Yes. The vacuum line to the pressure sensor should have a small piece of plastic stuck way down in it. It should have a small hole through the plasti piece.

If it falls on it's face and stays down on its face, it sounds like a secondary injector problem. Wiring.

If it falls on its face around 35-3800, then recovers the rest of the way to the rev limiter.....then is possibly the grounds for the ECU/engine. Make sure that the ground strap/wire from the right side of the transmission to the firewall is on plus the large ground attached to the starter bolt is secure/clean. The ground problems for the ECU should have been fixed by Mazda by the time your car was built. If not they were derilict in their duty.

If the secondary injector wiring plugs have a sign of being replaced....look for bad splices a the new wires/piggyback/splices.

yearrgh

I updaded the other post, but forgot this one. It turns out that the rear leading spark plug wire was broken off at the boot. Figures, I checked the other 3 to make sure they were in the right place and assumed that that one was as well. Lazy me. Anyhow, he fixed that and it runs fine now, but I still don't understand how that would cause a problem like he was having... Thanks again for the help.