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Discussion Starter · #1 ·
Anyone out there that can point in the right direction with this particular issue would be greatly appreciated.
Ill start from scratch:
At this very point in time the engine will start, rev to about 2k, then fall on it's face. Will run a bit longer if you keep your foot on the throttle, but it really doesn't want to. I've had a weird idle for years and can never figure it out. Now its to the point where I can't get it to idle.
Things I've done:
Checked absolutely everywhere for vacuum leaks.
Plugs, wires, cap, rotor and ignition coil. Clean wire harness regarding the ignition system
Coolant temp sensor on the water inlet
Fuel filter
Throttle body and IAC removal for cleaning (just found resistance values for testing, but they're for operating engine
temperature and the engine won't idle)
Clean wire harness regarding the throttle body and IAC.
EGR removal for cleaning. Found that it won't seal 100% even after cleaning so I replaced it with fully functioning EGR and new gasket. EGR vacuum relief port is not plugged.
Calibrated the TPS to WSM specs.
Set ignition timing (yes, test connector was grounded)
Checked MAF for operation and cleanliness.

I can't think of much more. If I missed anything, or wasn't thorough enough with testing or cleaning, please let me know. Right now, I'm looking at the IAC, but cannot find a replacement anywhere online. I have a spare, but it was removed from a non turbo, auto trans throttle body. Does anyone know if there is a difference between the M/T IAC and the A/T IAC?

Any guidance or suggestions are appreciated.
Thank you
 

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The 88-92 BAC/ISC valves (IAC) are all the same (auto/5speed/Turbo/N/A).

1-Does the ECU throw any codes with the test connector grounded? If not disconnect the turbo solenoid or TPS or IAC and see if those codes show up.
2-Jump the yellow connector next to the test connector and confirm there is fuel running through the fuel rail (you can feel it in the rubber hoses, hear it in the rail and feel the FPR get cool...)
3-Check for continuity between the distributor wires and ECU. Instructions in this thread: 1G F231 eca availability/interchangeability

You say the car revs to about 2000rpm and needs throttle to keep running but doesn't want to. If you try driving it does it sputter, arc and break up?

Most of the things you have checked won't prevent the car from revving past 2000rpm.

I don't want to send you down the wrong path but your symptoms sound like the ECU has failed.
 

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Discussion Starter · #3 · (Edited)
The 88-92 BAC/ISC valves (IAC) are all the same (auto/5speed/Turbo/N/A).

1-Does the ECU throw any codes with the test connector grounded? If not disconnect the turbo solenoid or TPS or IAC and see if those codes show up.
2-Jump the yellow connector next to the test connector and confirm there is fuel running through the fuel rail (you can feel it in the rubber hoses, hear it in the rail and feel the FPR get cool...)
3-Check for continuity between the distributor wires and ECU. Instructions in this thread: 1G F231 eca availability/interchangeability

You say the car revs to about 2000rpm and needs throttle to keep running but doesn't want to. If you try driving it does it sputter, arc and break up?

Most of the things you have checked won't prevent the car from revving past 2000rpm.

I don't want to send you down the wrong path but your symptoms sound like the ECU has failed.
Thank you for your reply man. I was hoping you'd be the guy to come through.

The engine will rev past 2k. Those are just the symptoms from just turning the key and without using any throttle. It's not very consistent with that though. Sometimes it'll run longer than others. Sometimes it'll fire up a bit, but won't run. When it does run, it smells super fuel rich.

I've replaced the o2 within the last year with an NTK. It is throwing a code 17. Something I noticed last time I was messing with it. The WSM I'm referencing is the '88 one, and I know there are some differences. It says in the '88 manual that code 17 is o2 sensor related however, it also says that if it doesn't throw a MIL then to suspect a vacuum leak, contaminated o2 or fuel injection issues. It does not throw a MIL and doesn't code for anything else but 17.

I've never replaced the injectors or pump. Never replaced anything on the fuel system besides the filter. I also haven't recently checked fuel pressure.

Before I had the throttle body off for cleaning, the car still had a funny idle, but would at least be able to keep running after a few minutes of warming. Aside from the poor idle, the car would drive pretty well, even during hard acceleration. It ran a long time under these conditions, but never quit, and would always restart. Now it seems like the same symptoms have worsened to the point where I won't road test the car.

I'm beginning to suspect a bad PCM as well, but I don't have another one and I don't think I've gone through all of my possibilities.

I'm leaving town tomorrow and when I get back I'm going to try the test procedures you had mentioned. In the meantime, if you can think of anything else with the info I've given, let me know. Also, let me know if there is anything you'd like me to check or any specs I can provide.

Again, I really appreciate your response.
 

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Discussion Starter · #4 ·
Found an ECM on ebay for half the cost of what it is for a reman from rockauto. The part number for the ebay one is "F220 18 881H" and the number on rockauto "F220-18-880J". Both say they fit an 89 mx6 gt. Is there any actual difference between the two or will either one run the engine?

Any response is appreciated.
 

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88-89 F2T ECU's are all interchangeable and will run the car the same, if there is any actual difference between them i have never noticed it.

I will sell you a working ECU with boost cut removal chip installed for 150$ + shipping.
 

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I read your reply to my 1st post when you wrote it, you ended with I'm going away will test when I get back.
Your next post was about purchasing an ECU so I offered one, did you do the other tests? How high can you get the engine to rev? Every blown ECU I have encountered wont allow more than 3000rpm, make more power at 2000rpm (10hp) and can barely move the car at 3000rpm (1hp) in 1st gear. I will be honest I never tried second gear because you know it's just going to get worse, runs just as bad in reverse. At idle and on throttle the ignition timing and fuel are way off, sputters, arcs, has mini backfires.
You say you are getting a code reading form the ECU, usually when they go they wont throw any codes.
Disconnect the ground at the battery and hold the brakes for a bit to reset the ecu, don't star the car just turn the key and check the codes, if the ECU is throwing codes properly (still functioning) and code 17 is still present it's a signal/wiring issue, if you have to start the car to get the code it's sensor or vacuum or mechanical related.
That being said code 17 isn't going to keep you car from running, O2 sensor will make it run rich, vacuum leaks will make it stall at idle but will run under throttle and the more gas you give it the better it runs because the vacuum leak becomes less significant. Fuel injection issue works in revers of a vacuum leak the more throttle and higher the fuel requirements the worse the car runs.

Check your engine and harness grounds.
The 1988 wsm will do for an 89 f2t.
You mentions it stalls after warm up, thats not a symptom of a blown ecu. When the engine reaches operating temps???
So the coolant temp idle valve should close and the electric idle valve should be the only thing controlling idle, one of the solenoid valves on the firewall opens or closes (in the book) the blue vacuum thingy under the intake manifold closes (it is screwed into the coolant section of the intake and bleeds off vacuum to the fuel pressure regulator and so does the firewall solenoid valve if I recall, both can be bypassed with the vacuum hoses without the engine throwing codes). O2 signals are used to control idle fuel, either they are used for enrichment maps during idle or injector duty cycles are fixed and the FPR does all the warm up enrichment by vacuum signals.

When a car gets to operating temp it can effect bad wires, the more heat a wire absorbs the less conductive it is for example a car that will only turn over fast enough to start when cold has a wire issue in or to the starter, when the wire heats it can't conduct enough amperage to run the starter motor fast enough. Every corroded strand of in a wire is one less strand transferring power at that point in the wire.

Use the manual and check stuff based on symptoms.

I'm not sure your ECU is the issue if your goind to buy one I will sell you one but because I suggested it could be the ECU if it turns out its not the ECU that makes me an asshole, if you buy it somehere else for more does that make me a bigger asshole. I want ti help you trouble shoot not buy more parts to swap, if your are going to buy an ECU just to try I will grab the ECU from my shop Sunday, box it and weigh it. We can figure out shipping options and cost Sunday.


The ECU I would sell you is sitting in a car that ran when it was parked a couple years ago. I don't have one that is running at the moment to test it in. I will replace it if you have issues.

Give me more info and I will give you more trouble shooting advice. I am working with a long list of swapped parts and a short list of symptoms.
 

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Discussion Starter · #8 ·
I read your reply to my 1st post when you wrote it, you ended with I'm going away will test when I get back.
Your next post was about purchasing an ECU so I offered one, did you do the other tests? How high can you get the engine to rev? Every blown ECU I have encountered wont allow more than 3000rpm, make more power at 2000rpm (10hp) and can barely move the car at 3000rpm (1hp) in 1st gear. I will be honest I never tried second gear because you know it's just going to get worse, runs just as bad in reverse. At idle and on throttle the ignition timing and fuel are way off, sputters, arcs, has mini backfires.
You say you are getting a code reading form the ECU, usually when they go they wont throw any codes.
Disconnect the ground at the battery and hold the brakes for a bit to reset the ecu, don't star the car just turn the key and check the codes, if the ECU is throwing codes properly (still functioning) and code 17 is still present it's a signal/wiring issue, if you have to start the car to get the code it's sensor or vacuum or mechanical related.
That being said code 17 isn't going to keep you car from running, O2 sensor will make it run rich, vacuum leaks will make it stall at idle but will run under throttle and the more gas you give it the better it runs because the vacuum leak becomes less significant. Fuel injection issue works in revers of a vacuum leak the more throttle and higher the fuel requirements the worse the car runs.

Check your engine and harness grounds.
The 1988 wsm will do for an 89 f2t.
You mentions it stalls after warm up, thats not a symptom of a blown ecu. When the engine reaches operating temps???
So the coolant temp idle valve should close and the electric idle valve should be the only thing controlling idle, one of the solenoid valves on the firewall opens or closes (in the book) the blue vacuum thingy under the intake manifold closes (it is screwed into the coolant section of the intake and bleeds off vacuum to the fuel pressure regulator and so does the firewall solenoid valve if I recall, both can be bypassed with the vacuum hoses without the engine throwing codes). O2 signals are used to control idle fuel, either they are used for enrichment maps during idle or injector duty cycles are fixed and the FPR does all the warm up enrichment by vacuum signals.

When a car gets to operating temp it can effect bad wires, the more heat a wire absorbs the less conductive it is for example a car that will only turn over fast enough to start when cold has a wire issue in or to the starter, when the wire heats it can't conduct enough amperage to run the starter motor fast enough. Every corroded strand of in a wire is one less strand transferring power at that point in the wire.

Use the manual and check stuff based on symptoms.

I'm not sure your ECU is the issue if your goind to buy one I will sell you one but because I suggested it could be the ECU if it turns out its not the ECU that makes me an asshole, if you buy it somehere else for more does that make me a bigger asshole. I want ti help you trouble shoot not buy more parts to swap, if your are going to buy an ECU just to try I will grab the ECU from my shop Sunday, box it and weigh it. We can figure out shipping options and cost Sunday.


The ECU I would sell you is sitting in a car that ran when it was parked a couple years ago. I don't have one that is running at the moment to test it in. I will replace it if you have issues.

Give me more info and I will give you more trouble shooting advice. I am working with a long list of swapped parts and a short list of symptoms.
Thank you again for you reply man. Honestly, I've been sort of vague as far as describing symptoms. I've been dealing with the issue for years and have not gotten anywhere with it myself and have not been given good troubleshooting advice. I've had a couple older guys look at it and they threw their hands up at it. So it's been pretty frustrating and I truthfully didn't think that I would be getting any helpful advice by posting to this forum, but here you are proving that wrong. So thank you again for that.

I've made a list of the things you wanted me to check. I also have some other troubleshooting flowcharts I've printed from the manual that I'll be working with today.

I can confirm that there is fuel running through the rail, still haven't gotten around to checking pump pressure.

I've reset the ECU and it is not currently giving me any codes.

Starting the car from a cold start: It will fire almost immediately. Will start to idle up to about 2k and begin to come down to an idle then will quit. All of that will happen in about 10 seconds.

Trying to restart the car after that: (engine is still cold) Will crank, but won't willingly start like it did initially. Get on the throttle while cranking and the engine will eventually fire and will run and die the same way it did from the initial cold start.

The engine will do that all day and never actually idle.

The engine will rev through the full range of rpm, but suddenly will start falling on its face. Give it throttle (about 50% throttle) to keep it from dying and it will sputter and breakup terribly (around 1k) then suddenly again will rev up and give me full range of rpm again. This cycle will repeat all day and never actually idle. Can't drive the car right now because of this.

This is the worst the problem has ever been. This is what I ended up with after I removed the BAC for inspection and cleaning. The BAC was very clean and it looked intact. Didn't really know what else I could do as far as testing its functionality. I made a new gasket for it and reinstalled along with replacing and cleaning other parts mentioned in my first post.

Last time I played with it: I disconnected the connector to the FPR solenoid on the firewall and the engine seems to run a bit longer and a bit smoother, but still dies after about 6 seconds.

Overall, the engine will not idle longer than 10 seconds. The ECU is not throwing any codes at the moment. Even after all the starting, running and restarting.

I'm going to try it all again today and go through the list of things to check you've given me. The only thing I may not be able to get to today is checking continuity on the distributor circuit. I'll need to bring my good meter home from work.

As for the ECU, I'll still take it. Whether my current ECU is bad or not, I'd like to have a spare and my current ECU still has boost cut. It's not very important right now that I have boost cut removal, it will be if I can get this engine running properly again.

Will be back later today with more info. Thank you again. let me know if there is a better more direct way to contact you about this.
 

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Discussion Starter · #9 ·
Reset ECU and checked for codes. No codes. Cranked the engine a few times and it started but just died. No idle at all. No revving to 2k and dropping. Just a few sputters. Didn't really try to get it to run today, but have had it running previously through full rpm range. Still no codes at this point.

ECU responds to disconnecting turbo solenoid and TPS. Threw corresponding codes as it should.

Checked and cleaned engine grounds all over.

I noticed today that the fuel pump sounds pretty loud and whiney. I've never changed the fuel pump since I've owned the car. I still haven't gotten a chance to check fuel pressure.

If you've got any suggestions for me given the new info, throw it at me. Otherwise, stay tuned and I'll get back to you with results from the continuity test. Also a fuel pressure reading.
 

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I recommend skipping the continuity test for the distributor wires and just untapping the harness from the dissi wires towards the injectors, you are looking for the point two wires are crimped to 1 (yellow and green tape), the crimp block causes corrosion and bad conductivity, eliminate it and solder the wires together.Preventive surgery at worst.

Your symptoms are hard to diagnose.
It does sound like you have a vacuum leak causing idle and stall issues but the way the engine runs under throttle sounds like a second issue.
Your ecu throws codes properly but "it stutters and breaks up terribly at 1000rpm" are the symptoms of a bad ECU but it could also be 1 bad signal from the dissi. Based on your last two post I do not suspect the ECU is your problem.
You could have a massive vacuum leak at or after the throttle body. You could try unplugging the air flow meter and seeing if the car idle or runs any better, with the AFM unplugged the ECU no longer uses it's signals to idle and run the car, if there is a vacuum leak between the AFM and TB thats causing the car to stall with the AFM disconnected the car will idle.
It could be the ISC valve (electric idle valve) thats attached to the bac valve isn't functioning properly and staying completely shut.
It can be tested using the workshop manual.

Have you checked the throttle body boot for cracks?

I have trouble shot and diagnosed hundreds of F2 motor issues over the years the workshop manual has helped a lot but sometimes old school/backyard mechanics is just as useful. I would remove the throttle body boot (throttle plates visible and exposed to the air), unplug the AFM harness connector and have someone start the engine (turn the throttle flap manually and remove the throttle cable from the flap so they cant operate the throttle and you have full control over it or it's their foot and the throttle flap vs your finger = foot wins) while I tried blocking the BAC/ISC holes in front of the throttle plates with my fingers to see if idle can be achieved and or controlled that way. If by blocking 80% of the air to the valve you can get the car to idle and you remove you fingers and the engine stalls it's the Bac/Isc valve, If you don't feel any vacuum on your fingers clean the area around the BAC/ISC ports and cover them with electric tape, hold both ends inside the TB with two fingers and try starting the car, if no suction pockets form over the ports in the electric tap the BAC/ISC valves are seized shut. You can allow more air to bypass the throttle body using the throttle adjustment screw, Trying this on a non running car can cause more issues, you must mark the crew driver slit position on the aluminum of the TB using a sharpy, one mark at each end of the slit, Then insert the screw driver and put a dot on the stem of the screw driver exactly at one of the sharpy lines on the TB, turn the screw driver counter clockwise and when the dot and line line up, stop and put a notch or number on paper and do your next counter clockwise turn and write it down. (You are probably thinking, I am not an idiot why would I write down every turn, I can just count them but only one method is foolproof). If you can achieve idle by backing off the idle bypass screw than return it to it's original position and replace the BAC/ISC valve.

I am focusing on your idle control valves because you worked on them and symptoms got worse.

You should also pressure test the system, connect a fitting and air in the air pipe system before the turbo and put about 10 psi into the system and check for leaks.
One kid I met had an issue with his car running, he had figured out to use a a drill driver for self tapping screws and a piece of a pencil through two holes he drilled in the black plastic air flow meter cover I believe what he told me was "I put the bit driver in the first hole when the car is cold and once it's warm I put the pencil in the second hole and remove the bit driver."
He was locking the air flow meter flap opened at different positions to keep the car running. It turns out his intercooler had a 4 inch slit in it along the upper tank to core edge. he was manipulating fuel delivery to the engine through the MAF to keep the engine running despite the giant vacuum leak. That was clever on his part but the car ran like shit, had to ride the clutch or it wanted to stall, it was twitch and wanted to go, boost came one and it was really slow ... so what the fu#@ a driver and a pencil??? Smart and clever but putting thought into bypassing the problem and suffering the consequences instead of figuring out the problem and resolving it isn't practical use of smart and clever.

I don't know exactly what symptoms his car was suffering before he "resolved them" with the pencil and driver but I do know the symptoms of a significant vacuum leak and he managed to bypass them by manipulating the air flow meter flap to control fuel.

So test 1- remove the air filter cover and move the flap while someone tries to start the car.
If it starts or idles better with more fuel (afm flap position)...
Test 2 - check for vacuum leaks in the whole system.
Test 3 - test the bac/isc system.

I know if you blow off an intercooler pipe and disconnect the AFM connector you can limp the car back home, pretty much the biggest vacuum/boost leak you can have before the TB just the throttle body sucking in air through a pipe. no boost no meter.

So I am leaning towards your issue being air to the engine and metering or control as your idle issue based on the symptoms. If there is a second issue than it can't be figured out until the car is idling and running.
 
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