Shainiac

iTrader: (7)

Heres the scoop, when my car is fully warmed up, it will not redline at all.
It acts as if there is a rev limiter at 3800rpm. It just bounces there until I back off the throttle.
At part throttle, i can rev slowly and smoothly to redline, but if I give it any more gas, it begins to cut out.

So, after grounding the ECU to the chassis and grounding the MAP sensor to the strut tower (early 86 model) the problem remains. I began to doubt my solder points, but grounding the ECU did make a difference. Low speed shuddering is improved as is flooding at startup. I found the instructions for testing the MAP sensor in the FSM, but I dont have a vac pump with a gauge.

Any advice?

Brody8877

iTrader: (10)

are you sure you do not have a clogged cat or if your secondary is firing up.

RotaryWeaponSE7EN

iTrader: (6)

Mine did that for a while, ended up being the fuel pump.

mario1386

sorry for the thread jacking,


but i got the same problem at like 6000rpms

Phantomkid

3800 rpms is a known ground problem search that and try not only grounding the ecu but the other grounds like under the intake manifold. Havce you tried checking for faults. Is this turbo or NA do you have a voltmeter? If so check voltage at the connector at the ecu with the connector still connected it should be i think around 2.6 if theres no voltage therew then you either have a bad map or bad wiring. Does it totally cut out. I had this problem when but with my emanage it would not put out the map signal so the ecu never recieved the signal it could rev up to redline but WOT would just die out. I would try checking for faults if you know how to check at the test connector i believe the MAP is one long 2 short if not look on teamfc3s they have a write up. Good luck

Phantomkid

as for mario you may have a fuel problem is your tank low? hook up a fuel pressure gauge watch it when driving see if it cuts pressure when at 6000 rpms. YOur problem sounds different being the rpm change does your problem also only happen at WOT

mario1386

well i have a new pump and filters and the tank is full.,and still does it.

Shainiac

iTrader: (7)

Please dont thread jack. Ive had enough trouble getting help in my other thread regarding this issue. The ground under the manifold is the same wires I grounded in the harness to the chassis. I am not sure how the car runs well at low loads over 3800rpm. The problem is non-existant when the car is cold. This is a rather large detail I forgot to mention in my original post. It will redline under WOT without a hicup before the thermostat opens.

The secondaries fire over 3800 regardless of load, correct? I tried unplugging the MAP sensor from the manifold and it ran worse and still had the hesitation.

-Alex

mario1386

sorry

farberio

iTrader: (7)

Just to get them out of the way have you verified that your 6 ports are working?

Shainiac

iTrader: (7)

Yes, they are working fine. This isnt a mechanical problem though. It is most definitely a electrical problem.

HAILERS

Testing the boost/pressure sensor: With the engine hot, engine off, key ON, check the output of the boost/pressure sensor with a meter.

Then with the engine hot and idling, check the output of the boost/pressure sensor with a meter. Write back what each was.

You'd read that with all plugs connected and read it at the boost/pressure sensors Brown/RED wire either at the sensor or at the ECU plug by back probing it.

It sounds like a secondary injector problem ...maybe. On these cars you can reach high rpms without the secondary injectors working by using light throttle pressure til you get there in the high rpms. Sounds a little like your car. But if hard throttle is put to it, the boost/pressure signal goes to zero and over 3800 rpm the secondarys are supposed to come online. Your car stumbles and won't advance past that 3800rpm if I read right.

Since it's a 86 non turbo you can reach the secondary injector plugs easily. Can you verify batt voltage on one wire of each of those injectors. Should be there. Matters not which of the two wires.

Pulling the vac hose off the boost/pressure sensor and plugging the hose, should result in the secondarys coming online in the driveway any time the revs are over 3800 rpm. If I do that on my car, and slowly rev the engine to 3800 rpm, the revs will get crummy at that speed (too much fuel for no real load), but IF memory serves, if I floor it the revs will go to red line. I'm not sure what good that information will do you.

There is a safe way of seeing if the ECU is pulsing the secondary injectors using a LED light (and ONLY a LED light). I can play around and refigure that out if your interested.

In general, does this car idle and run fairly well just driving around the block??? Aux ports not opening should not be your problem. I can disable the feed to my aux ports and redline without stumble.

Has this car ever run good for you? This present problem a new problem? If it never ran good at 3800 rpm, maybe the previous owner installed tooooo large injectors in the secondarys. The last numbers on the side of the injectors should read -1350. Written on the side of the elect jack on the injectors.

HAILERS

You could buy a LED from Radio Shack as shown in the first jpg attached.

I pulled the REAR secondary plug off. I put the RED wire of the LED in the socket that had a brown/yellow wire. The other LED wire goes in the other injector plug socket.

Vacuum line off the boost sensor and the line plugged. Start the engine. Rev the engine from the engine bay. LED will light up when you hit approx 3800 rpm and then the engine will pulse (due to primary injector duty cycle being halved and the seondary coming online). The LED will pulse on off with the engine pulsation. Now rev the engine full throttle. LED light stays on all the time. This more than less proves the ECU is good.

Do the same with the FRONT secondary. Red LED wire to the light green/white wire and the other LED wire in the other socket. Repeat the above.

If you get the LED wires in the wrong socket, you will get no light. NO harm done to anything if you do that. Just swap the LED wire around and try again.

The only way you could harm anything is if both LED wires touched eachother for a prolonged period of time while the engine was running or key to ON and they are touching each other.

With the meter on the brown/red output wire of the boost sensor and all connectors on the engine/car, and key just to ON, the reading is 3.53 vdc. Then with the engine at idle of 750 rpm approx and fully hot, the reading is 1.56vdc. It might bounce a little b/t 1.50 and 1.60vdc. Not to worry.

The very first time I ever changed out vacuum hose on a RX, it ran crummy as I drove down the street for the first time. I went back and discovered that the boost sensor vacuum line on the original hose has a orifice in it to prevent surging at the boost/pressure sensor. I put the orifice in the new line and all was well. You might check for this item in your pressure sensors hose. Just a thought. Part number is in a old thread. Search for HAILERS and ORIFICE. Also NZCONVERTIBLE wrote about this and how to make a orifice. He might have called it a "pill" (wrong fricking name, sorry 'bout that).

This site: http://www.teamfc3s.org/info/article...odes/main.html lists some ideas on LED usage and Radio Shack part numbers etc.

HAILERS

One last thought is the solenoid resistor package mounted on the fender below the afm/airfilter. Some people have said they had a bad one.

Easy to figure out. Pull it out of the car. Ohm it out. You ohm from the middle wire to each of the other wires one at a time. The resistance should be SIX ohms give or take one ohm.

https://www.rx7club.com/showthread.p...ighlight=DRILL

EDIT: About my post above this. Over 3800 the LED should shine steady. Under 3800 rpm no LED light. At 3800 rpm and engine pulsing.......LED comes and goes.

Shainiac

iTrader: (7)

Wow, that is a lot of awesome information. Unfortunately I dont have time to work on the car today, but I should have some useable hours of daylight tomorrow. I am a bit ignorant when it comes to using a multi meter. When backprobing the MAP sensor at the plug, the RED probe on the multimeter goes to the Brn/Red wire and the BLACK probe goes were? Excuse the stupid questions, but Im new to electronics.

As for the car, daily driving and fuel mileage are as good as before this problem started. As long as I keep the revs under 3800 or the load low, the problem isnt apparent. At first, the car would only have this problem intermittently, but as time passed, the problem grew more frequent until the point that it happened every time the car was hot. I am still curious as to why it redlines fine when cold (temp below 1/4 and my mech temp gauge reading 0* post thermostat)
One thing I though might be worth mentioning, I replaced a few of my injector clips about a year ago. The crappy clips that were on there before had trouble making connection and would Blow the EGI fuse which makes me think it is not a bad connection, but I suppose it could be no connection at all? I could be possible that I swapped wires when putting the new clips on the old harness. Would this be a problem?

Thanks again for all the great info and I will report back tomorrow with readings and hopefully LED results!

HAILERS

Negative meter lead goes to any good ground. The bracket that holds the pressure sensor on is grounded pretty good. Use it. Meter on DC Volts. Leave the elect plug connected to the pressure sensor.

HINT: unbolt the pressure sensor and turn its elect plug up instead of down. That way you can access the brown/red wire easily. Remove the vacuum hose and plug it so you can turn the sensors elec plug up instead of down easier.

EAch injector plug has two wire. It matters not which wire goes in which socket when talking about those two wires. BUT, pay attention to the color of the wires I mentioned in the post above. The LED RED wire must go where I said. If it's not easy to determine the color b/t the two wires, just try it one way and then the other way with the two LED wires. You can't hurt the ECU by swapping the LED wires.

Here's a easy one. Get a LED. Put one wire to gnd. Turn the key to ON. Put the RED LED wire in first one of the injector plugs sockets then the other. The LED should light up when you put the RED wire to the injector wire that has power, proving the injector is getting batt voltage.

Or just go to the battery. Put the RED LED wire on the pos batt terminal and the other LED wire to the neg batt terminal. LED should light up if any good. NOW swap the LED wires. The LED should not light up becasue there is a blocking diode inside it to prevent it from lighting up. Just do this to gain confidence with the LED light. No other reason to do that.

NoDOHC

SpeedOfLife had a similar problem, it turned out that his TPS was not reading fully open. This is something else that you can test.

Shainiac

iTrader: (7)

I unplugged the TPS last night and drove around for a bit. Iirc, this trips the ECU into seeing a default reading of WOT, correct? Anyways, the problem persisted so Im assuming the TPS is not the culprit.

HAILERS

Yes. The TPS defaults to a 100% open value (signal inside the ECU) if it's unplugged. The idle will turn bad/irregular on you if it's disconnected.

Shainiac

iTrader: (7)

Sooooo, I broke out the multimeter and got some numbers for my MAP today.
Before you see the numbers, keep in mind that my car has a large street port and what I think is a vacuum leak somewhere in actual throttle body. The car idles on its own but only when warmed up. I still manage to get ~22mpg, so Im assuming its not a huge leak or the MAP would be reading more load, but it would explain the higher readings at idle. After rebuilding the motor in December, I have torn the intake apart 3 times and put new gaskets or RVT between every surface with no luck. When pressure testing the manifolds, I do get a leak somewhere between the TB and the upper intake but its rather vague. That said, Im sure this and the porting throws the idle readings off a bit.

Engine off and hose plugged - 3.51v
Engine running, hose connected, 800rpm 2.1v
Engine running, hose plugged - 3.50v
If I pumped the throttle with the hose connected, the multimeter would spike to around 3.3-3.4 from what I could tell, but its a cheap multimeter, so who knows.

LED test:
I pulled each secondary clip and inserted said RadioShack LED. When revved in neutral with the vac line plugged, the engine would cut out at 3800 and the light would shine solid. This leads me to believe these are not the problem.

I am pretty unfamiliar with the resistor box under the AFM for the low imp injectors. I am pretty sure I have located it, just ignorant on where to take readings and what to look for. What is the likelyhood that the ECU is bad? Is there any way to check this other than swapping in a known good one? It would make since that the temperature would effect it if the ECU was haywire since it controls the secondaries and gets readout from the thermosensor, but that is a complete shot in the dark.

Hope this helps you help me!
Thanks

turboIIrotary

iTrader: (9)

do you have the right injectors in it? my friend has a turboII that he bought from someone and they put bigger secondaries causing it to flood out.

HAILERS

Well your getting power to the secondarys and also getting the pulsed ground from the ECU. The solenoid resistor pack is probably ok then.

The 2.1vdc reading is a bit high, but that could be lack of enough vacuum on the sensor at idle.

I'd check the numbers embossed on the side of the secondarys. Ends with -1350 for a eighty six model car.

Sounds like too much fuel when the secondarys come on. Could be too large secondarys or could be a defective AFM. No REAL way to tell if the afm is good/bad imho.

You might look to see if the large black cover on the afm has been tampered with. If it has, someone could have been playing with the afm's internal spring tension and kinda fucked it up.

The black cover is missing on the afm in the jpg. It is D shaped and black and covers the internals shown in the jpg. Tampering would be looking to see if the RTV around the edges of the black cover is missing, or is some color other than aged, clear RTV. Hard to describe.

It sounds like just tooooo much fuel. When you hit 3800 rpm under LOAD, the secondarys come online. At the same time, the primarys duty cycle is cut in half. Like if the primarys duty cycle was 80% prior to 3800 rpm, now it's 40% and the duty cycle for the secondarys is also 40% the moment the secondarys come online. And the duty cycle for both will go up the same precentage as you keep your foot in it.

I'm outta ideas. Anybody have a idea throw it in there.

HAILERS

Not when cold. Goes against my instincts, but pull the green connector off the water thermo sensor on the back of the water pump Housing. Look at the terminations inside the harness plug. Are they even with each other? or is one pushed back and won't make contact with the water thermo sensor if the plug is installed again? Geen, two wire plug. BACK of the water pump HOUSING. Can almost be accessed without removing the ??? alternator? I forget.

Shainiac

iTrader: (7)

If I have time Ill check the thermo sensor tomorrow. I may the actual sensor with a know good sensor I have laying around also. I am 99% positive this is an electrical problem causing the secondaries to not fire rather than too much fuel. I wish I had a descent video camera to take a clip in-car. As for the off chance of the PO messing with things, Ive owned the car for a couple years now. For the first entire year it ran like new. It wasnt until It got rebuilt for a coolant seal failure that things just starting showing their age. Ill check the injectors for peace of mind, but Ive had them out multiple times and all 4 are identical redish orange injectors. I had them cheaned at a reputable diesel shop locally, but I turned all 4 in at once and dont seem to have a problem with my primaries. Im just about ready to caugh up the dough for a megasquirt and say hell with the fried stock wiring harness and sensors.

Lastly, is there any real way to verify the ECU is not the culprit? Its nice to check all the obvious problem areas first, but how often do they really fail? The only local S4 junker got sent to the crusher a few months ago, so it may be worth my headache to try a used one after my vacation next week.

HAILERS

The ECU can be checkout by going to the page called CONTROL UNIT in the FSM. Look in FUEL AND EMISSIONS section. You'll find the readings for each pin on the ECU plugs. Like this: https://www.rx7club.com/attachment.p...2&d=1215530506

You unbolt the ECU so you can tilt the ECU up where you can get at the wires in the plugs. You put your meters negative lead on a known ground like the bracket that holds the ECU in place. You put the meter on DCVolts. Then you probe each wire, one at a time and compare the reading to the CONTROL UNIT page. You back probe each wire using something like a sewing needle or equiv. The plugs stay attached to the ECU.

There's a post yesterday just above or below your thead with the same problem. They claim replacing the Solenoid Resistor solved their problem. But they called it something else if memory serves(Variable Resistor package is what they called it). There is nothing variable about the resistors inside the Solenoid Resistor Package.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/wont-rev-past-4k-769788/ They called it the variable resistor pack. There is no such thing on a RX. Soooooo one has to *** u ME they mean the Solenoid Resistor Package that is under the afm/airfilter and bolted to the fender. It has six ohm resistors that feed the fuel injectors power. Personally I don't see how these resistors can go bad, but others in the past say replacing that item fixed their problem. I'm a doubting Thomas myself on that having been the problem, but..........

There is a Variable Resistor on series four cars. IT effects the idle fuel only, never the fuel above idle