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Discussion Starter · #1 ·
Hey guys, Im writing here as it´s probably the best site for MX6s/Probes and Im desperate.

I have 1993 Ford Probe GT (V6 KLDE) that won´t rev past 5500 RPM. But it did before! I replaced my valve cover gaskets and obviously I screwed something up.
I read codes from memory and got a bunch of them, so I starterd to chew through them. Now, my memory is clear and I don´t get any check engine light, but it still won´t rev past 5500 RPM.

I replaced my distributor with spare one, had the timing adjusted with timing light and the TPS as well. It didn´t help.
I replaced both coolant sensors (Fan and ECU one, not the dash one with single pin). It didn´t help.
I replaced the plugs and wires. It didn´t help.
Some time before this, about a year ago I also replaced my fuel filter.

I had a single code left after all this. #5, the knock sensor... And yeah, I admit it, I accidently ripped the wires when taking off the manifold.
I fixed the wires, cleaned the memory and went for a drive. The code is gone.
Now I have no codes when I read the memory, no flashing or glowing check engine light, but I still can´t rev past 5500 RPM! :-(

I had some opinions given on my problem by other guys from our community, they suggested:
1) To replace the solenoid on air intake. Already did that.
2) To replace the Fuel pressure regulator (I didn´t do that yet)
3) To replace my spark plugs, as apparently, while I did buy NGK ones, the ones I got are "Too cold".

What do you guys think I should do? Can the signal from Knock sensor be distorted because of the wire accident?
 

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Discussion Starter · #3 ·
I would start by checking for intake manifold air leaks and make sure all the engine grounds are attached and in good condition. Does the KLDE ecu limit rpm during knock or does it just pull timing like most N/A engines?

Also you can try these:
PMX626.info //US/Ford Probe/Manuals/1993 Electrical and Vacuum Troubleshooting Manual/

http://www.pmx626.info/US/Mazda 626 & MX-6/Work Shop Manuals/PDF/1994 US WSM_OCR.pdf
I already went through the manifold. The plastic part behind VAF is tight and non leaking. I found 1 broken hose that went to first VRIS and I replaced it, which fixed about 3 of my codes (Vris 1, Vris 2 and strangely code #16).
As for the engine grounds... Yikes, I´ll have to check those.

Im not sure to be honest. I know that during certain error codes (Like water temp. sensor), it will rev limit at 5500 RPM. If it detects knocking, it should retard the timing to 10°.

It is not knocking on idle and it drives very nicely all the way until VRIS 2 opens, then it goes for a few hundred RPM and once it gets to around 5000-5100-5200 or so it suddenly looses the will to rev further (Basicaly as if the engine is not getting enough air), it starts to jerk a bit and once it revs a tiny bit over 5500 RPM then it kicks back like hitting rev limiter.
 

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My experience is that check engine lights usually don't effect RPM limits, or very few ecu's lower RPM based on trouble codes, if the ECU doesn't get an O2 sensor reading it will run a default rich fuel map (limp mode) and the engine will run like crap all the way to factory redline (rpm cut).

So if it's not an electronic issue, it's a mechanical one.
My first thought was vacuum leak because you have to remove the manifold to change the valve cover gaskets.
An intake air leak after the air meter can result in the engine sucking in unmetered air and the ECU won't deliver enough fuel to match the amount of air the engine is getting.

Insufficient, missing and broken engine grounds can lead to spark failing at higher rpm when the current gets higher and the ground path is insufficient. Your symptoms sound the same except the engine breaks up after a certain rpm like it's misfiring (because it is).

Read the trouble shooting guides in the 1994 MX6 workshop manual I linked, work your way through the steps.
Stop randomly changing parts (I have done the same thing in the past), you can introduce more problems or issues by swapping parts.
 

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Discussion Starter · #5 ·
My experience is that check engine lights usually don't effect RPM limits, or very few ecu's lower RPM based on trouble codes, if the ECU doesn't get an O2 sensor reading it will run a default rich fuel map (limp mode) and the engine will run like crap all the way to factory redline (rpm cut).

So if it's not an electronic issue, it's a mechanical one.
My first thought was vacuum leak because you have to remove the manifold to change the valve cover gaskets.
An intake air leak after the air meter can result in the engine sucking in unmetered air and the ECU won't deliver enough fuel to match the amount of air the engine is getting.

Insufficient, missing and broken engine grounds can lead to spark failing at higher rpm when the current gets higher and the ground path is insufficient. Your symptoms sound the same except the engine breaks up after a certain rpm like it's misfiring (because it is).

Read the trouble shooting guides in the 1994 MX6 workshop manual I linked, work your way through the steps.
Stop randomly changing parts (I have done the same thing in the past), you can introduce more problems or issues by swapping parts.
I was thinking it also theoreticaly might be an alternator issue? The voltage gauge on the dash was right in the middle of "normal" when I bought the car 4 years back, but oil has been dripping on the alternator for about a year until I changed the gaskets and now it only goes slightly above "n" in "normal".
 

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I was thinking it also theoreticaly might be an alternator issue? The voltage gauge on the dash was right in the middle of "normal" when I bought the car 4 years back, but oil has been dripping on the alternator for about a year until I changed the gaskets and now it only goes slightly above "n" in "normal".
Unless your having to charge your battery every couple days than the alternator would be working enough to keep the car running. If the battery was weak and the alternator was undercharging than yes it could effect the engine at higher RPM when power demands are higher but you would notice dimming lights and radio cutout before that happens. And when electrical draw on the system was lower, dash fan, cooling fan, radio, headlights... are off the car would rev higher and have no issues.

Did you unplug the distributor or crank sensor during your valve cover gasket swap?
A poorly connected or weak crank or cam sensor signal going back to the ECU could break up or pick up interference at higher rpm affecting the ECU's ability to run the engine. (often happens to people running standalone and custom crank trigger wheels if the sensor ins't perfectly positioned, the engine runs fine up to a certain rpm then the ECU no longer gets a clear crank/cam position signal and can't run the engine).
 

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Discussion Starter · #7 ·
Unless your having to charge your battery every couple days than the alternator would be working enough to keep the car running. If the battery was weak and the alternator was undercharging than yes it could effect the engine at higher RPM when power demands are higher but you would notice dimming lights and radio cutout before that happens. And when electrical draw on the system was lower, dash fan, cooling fan, radio, headlights... are off the car would rev higher and have no issues.

Did you unplug the distributor or crank sensor during your valve cover gasket swap?
A poorly connected or weak crank or cam sensor signal going back to the ECU could break up or pick up interference at higher rpm affecting the ECU's ability to run the engine. (often happens to people running standalone and custom crank trigger wheels if the sensor ins't perfectly positioned, the engine runs fine up to a certain rpm then the ECU no longer gets a clear crank/cam position signal and can't run the engine).
Alright, so the alt should be fine then.

No, I didn´t touch the distributor or the crank sensor while doing the gaskets, but I did unplug the distributor when I was swapping it for new one. It is connected properly and tightly though, I was checking just now.
 

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Discussion Starter · #8 ·
Unless your having to charge your battery every couple days than the alternator would be working enough to keep the car running. If the battery was weak and the alternator was undercharging than yes it could effect the engine at higher RPM when power demands are higher but you would notice dimming lights and radio cutout before that happens. And when electrical draw on the system was lower, dash fan, cooling fan, radio, headlights... are off the car would rev higher and have no issues.

Did you unplug the distributor or crank sensor during your valve cover gasket swap?
A poorly connected or weak crank or cam sensor signal going back to the ECU could break up or pick up interference at higher rpm affecting the ECU's ability to run the engine. (often happens to people running standalone and custom crank trigger wheels if the sensor ins't perfectly positioned, the engine runs fine up to a certain rpm then the ECU no longer gets a clear crank/cam position signal and can't run the engine).
You don´t happen to know what should be the voltage value for normaly operating knock sensor?
 

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Same problem has our friend (my and ChrisNotEvans) with basically the same Probe (93 KLDE). He tried everything, last time knock sensor (new one of course) and it doesnt helped.
Always the same story, diagnosis saying "everythings OK" but when you reach 5500RPM power is gone.
Its really strange.
 
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