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View Full Version : Completely, absolutely lost on an MKIII Supra.



Chris
08-09-2008, 02:35 AM
Sorry to post this here guys, but my thread on supramania has stopped garnering responses, so I figured I'd see what you guys had to weigh in.

I've got a 7MGE 3.0 6L 1986.5 Supra.

We've been having problems with it lately. What the car does at the moment is misfire. A simple enough problem, but my dad and I are completely lost as to the cause.

When you start it up, it will miss a bit at idle. Enough to be annoying, but the RPM meter holds pretty steady. As the car warms up, the misses will get a bit worse, but will still be drivable. The low-end torque is pretty bad, until you hit about 3200 RPMs. Then the motor smooths out completely and runs like a scalded dog.

If you keep it warm, you can start it up, restart it, whatever, and as far as I know it continues to run pretty well.

But if you let the car sit for awhile (15 to 30 minutes) and start it back up, the motor loabs/hunts at idle. It's a rhythmic shudder.

We've checked for vacuum leaks by spraying carb cleaner while it's loabing, but no luck. We plan to test it with a vacuum pressure tester.

This is what we have replaced on the motor so far:
Spark Plug Wires
Spark plugs have been checked and gapped
AFM
Throttle Position Sensor
Idle Speed Control has been cleaned
Plug galley is clear of oil and shit after we changed out the valve cover gaskets.


We still need to check the fuel pressure. Bypassing the fuel pump relay (switches the fuel pump from low to high, IIRC) doesn't do anything for the loabing.

The car also seems to run pretty rich. I can see how that may cause the misfire, or the lack of low end torque, but I'm not sure on the loabing after it warms up and sits.

So I'm completely lost. I really want to drive this car when I start to school next week, but at this rate it looks like I'll be taking the Celica unless I can get this problem fixed. So I need help here guys, I'm in a time crunch and if I need to order any new parts I need to do it fast. If you've taken the time to read this far, thanks. Any suggestions will be appreciated.

alltracman78
08-09-2008, 02:47 AM
Any particular cylinder[s], or all of them?

Have you checked your coils?

Have you ran it with a vaccum gauge on it?

Done a leakdown test?

Chris
08-09-2008, 02:58 AM
Any particular cylinder[s], or all of them?

Have you checked your coils?

Have you ran it with a vaccum gauge on it?

Done a leakdown test?


I honestly can't tell on the first one, whats the best way to check, just pull out plugs until it stops loabing?


On the coil, when we were timing the thing with the light we had the wire partially out of the distributor. That spark was still jumping pretty far, so the coil has to be pretty healthy.

We plan to put a vacuum gauge on it come Monday. No leakdown test. Could this be a blown headgasket?

T-spoon
08-09-2008, 03:09 AM
Heh, every problem on a 7M is a BHG. :hehe: I kid, I kid...








... but no really.

Obviously pay more attention to alltracman :)

Chris
08-09-2008, 03:19 AM
Heh, every problem on a 7M is a BHG. :hehe: I kid, I kid...








... but no really.

Obviously pay more attention to alltracman :)


God, I hope not. If it is then the car probably won't see action until winter break at best. Damnit. :(


I know the local mechanic has at the very least a compression test, we'll see what that does. We'll try and get a hold of a leakdown tester though. It's the only sure way to find out if this could be a BHG.

On that note, would spraying the head gasket with the carb cleaner do anything to help diagnose the problem?

alltracman78
08-09-2008, 03:22 AM
I honestly can't tell on the first one, whats the best way to check, just pull out plugs until it stops loabing?
Pull wires, 1 at a time.
If you have a problem cylinder[s] when you pull the wire it either won't effect the engine at all or will effect it less [if the cylinder is only partially misfiring the engine will still run worse without it].



On the coil, when we were timing the thing with the light we had the wire partially out of the distributor. That spark was still jumping pretty far, so the coil has to be pretty healthy.
Possibly.
I didn't know any of the 7M had dist, I was under the impression they were all coils...

The coil could still be bad, but that does make it less suspect.

IMO I would change your cap/rotor and plugs [just throw in a set of coppers for now, but make sure you use NGK] just to be sure.
Cheap insurance.


We plan to put a vacuum gauge on it come Monday. No leakdown test. Could this be a blown headgasket?
Possibly a mechanical problem, it would be a good idea to rule that possibility out before you go too far.

T-spoon
08-09-2008, 03:24 AM
Yeah, 7MGE use a distributer while the GTE has the coils and then the cam position sensor... I think where the dist. is on the GE.

alltracman78
08-09-2008, 03:47 AM
Ok, good to know. :)

I've only worked on the turbos.

Chris
08-09-2008, 07:10 AM
Pull wires, 1 at a time.
If you have a problem cylinder[s] when you pull the wire it either won't effect the engine at all or will effect it less [if the cylinder is only partially misfiring the engine will still run worse without it].

Okay. Stupid question here, any way I can pull the wires off the cap or will that shock the hell out of me? Two of my spark plugs are completely blocked by the throttle body.




Possibly.
I didn't know any of the 7M had dist, I was under the impression they were all coils...

The coil could still be bad, but that does make it less suspect.


Yep, cap and rotor on the N/A model 7mge.



IMO I would change your cap/rotor and plugs [just throw in a set of coppers for now, but make sure you use NGK] just to be sure.
Cheap insurance.

Forgot to mention that the cap and rotor have been changed.



Possibly a mechanical problem, it would be a good idea to rule that possibility out before you go too far.

Sounds good. I guess we'll see how far we can get.

Murgatroy
08-09-2008, 07:12 AM
Yes, you can pull the wires off the cap without fear of being shocked.

GT400
08-09-2008, 01:58 PM
Yes, you can pull the wires off the cap without fear of being shocked.

as long as you aren't touching the car. after zapping my hands numb countless times, it seems the trick to not getting shocked is to not have yourself grounded to the car. so avoid touching bare metal with bare skin and you should be all set.

as far as your misfire, a leakdown test will be very telling, make sure you do it with the radiator cap off, and watch for bubbles.

Does the car overheat at all? does it use any antifreeze?

My first toyota was an 86.5 supra. Mine blew the head gasket big time, emptying the coolant system in about 4 minutes. it was ugly.

The 7mge motor was no torque monster, but it sounds like youre down on power, especially if you have a noticable misfire.

good luck,
Daniel

Chris
08-09-2008, 03:40 PM
as long as you aren't touching the car. after zapping my hands numb countless times, it seems the trick to not getting shocked is to not have yourself grounded to the car. so avoid touching bare metal with bare skin and you should be all set.

as far as your misfire, a leakdown test will be very telling, make sure you do it with the radiator cap off, and watch for bubbles.

Does the car overheat at all? does it use any antifreeze?

My first toyota was an 86.5 supra. Mine blew the head gasket big time, emptying the coolant system in about 4 minutes. it was ugly.

The 7mge motor was no torque monster, but it sounds like youre down on power, especially if you have a noticable misfire.

good luck,
Daniel


Car uses a bit of anti-freeze, last I checked, but I figured that was because it has a leak somewhere around the heater core.

Nah, the car doesn't overheat at all.

But it's looking more and more a blown head gasket may be the issue here.

Some people on supramania finally responded and suggested to test the water temp sensor, read the VF signal going to the ECU, test the cold start injector, and some other things. I'll get back to you guys with the results.

JEDI
08-09-2008, 06:57 PM
Sounds like the head gasket has a small leak. The reason it runs ok after it warms up is when the engine warms up and the parts expand they seal. Also the antifreeze thing is a sure sign. You could just try retorquing the head bolts because on all mk3 supras thats a problem. When they were made at the factory toyota underestimated the torque on these bolts.

Chris
08-09-2008, 08:58 PM
Sounds like the head gasket has a small leak. The reason it runs ok after it warms up is when the engine warms up and the parts expand they seal. Also the antifreeze thing is a sure sign. You could just try retorquing the head bolts because on all mk3 supras thats a problem. When they were made at the factory toyota underestimated the torque on these bolts.


But wouldn't it do it at start up if warming up the engine closed the gap? And it only does it after it has warmed up and set. The longer I let it set after I warm the motor up, the better the idle gets.

While testing the water temp sensor's resistance, I noticed that the car would not start without it. It ran rougher when the sensor was not plugged in, once we plugged it in the engine smoothed out a bit.

Alltracman, Plugging the plug wires out of the cap didn't do anything for the motor, the lope got worse when the wires were unplugged. Plugging them back in and revving the motor smoothed it out.

andy
08-09-2008, 09:32 PM
got a 86.5 supra sitting in the drive now. its my dads, no 7mge though. its a 1jz now :) good luck gettin it goin. replace cap and stuff. also check your idle air control valve. and some seafoam. and get some compression results.

Chris
08-09-2008, 09:38 PM
got a 86.5 supra sitting in the drive now. its my dads, no 7mge though. its a 1jz now :) good luck gettin it goin. replace cap and stuff. also check your idle air control valve. and some seafoam. and get some compression results.

I'm planning on running some injector cleaner through it once the tank is mostly used up.

We reset the ECU so we could try and get an accurate error code reading. I'm going to get out and drive it tonight and see if anything other than a code 43 (starter) comes up.

JEDI
08-10-2008, 07:16 AM
Well theres different possibilties at startup that would not be there after running. Such as : if the had gasket has a small leak between the cylinder and a coolant run it wouldnt leak as bad at first startup because when the engine is cool the coolant isnt under pressure. As it warms up the coolant gets hot and creates pressure in the coolant system then more is forced in the cylinder. But as it reaches the engines peak operating temperature it expands the head enough to seal the leaky gasket.

andy
08-10-2008, 04:45 PM
leave the rad cap off and let it run and see if the burp does anything.

Kiasis
08-10-2008, 04:53 PM
insert ignorant and probably useless comment here --> I had my 3SGE diagnosed at Toyota via a leak-down test as a blown HG (coffee colored coolant, bubbled up at radiator cap, whole bit). When I finally got it torn apart, the HG was fine. Absolutely no tears, holes, etc. Turns out I had a slightly warped head. Coolant was seeping around the HG (when in the unpressurized cold to swollen pressurized hot cycle, I don't know) and all my pistons had cracked ring lanyards and pitted heads as a result. I have no idea if this could be applicable to the 7MGE, but something else to toss in the hat.

Chris
08-10-2008, 07:18 PM
insert ignorant and probably useless comment here --> I had my 3SGE diagnosed at Toyota via a leak-down test as a blown HG (coffee colored coolant, bubbled up at radiator cap, whole bit). When I finally got it torn apart, the HG was fine. Absolutely no tears, holes, etc. Turns out I had a slightly warped head. Coolant was seeping around the HG (when in the unpressurized cold to swollen pressurized hot cycle, I don't know) and all my pistons had cracked ring lanyards and pitted heads as a result. I have no idea if this could be applicable to the 7MGE, but something else to toss in the hat.

Did you experience any power loss, or symptoms other than the coolant?



leave the rad cap off and let it run and see if the burp does anything.


Just take it off, warm the car up and see if any bubbles surface?

quark
08-10-2008, 07:20 PM
I am pretty sure that it is your EGR Valve that gets stock open... It sound pretty much like that.

T-spoon
08-10-2008, 08:25 PM
insert ignorant and probably useless comment here --> I had my 3SGE diagnosed at Toyota via a leak-down test as a blown HG (coffee colored coolant, bubbled up at radiator cap, whole bit). When I finally got it torn apart, the HG was fine. Absolutely no tears, holes, etc. Turns out I had a slightly warped head. Coolant was seeping around the HG (when in the unpressurized cold to swollen pressurized hot cycle, I don't know) and all my pistons had cracked ring lanyards and pitted heads as a result. I have no idea if this could be applicable to the 7MGE, but something else to toss in the hat.

Checking the head for warp is something that should be done when diagnosing to find out why a head to block seal failed, so a diagnosis of the head gasket is a broad thing, it doesn't necessarily mean the HG itself failed.

Chris
08-11-2008, 02:26 AM
I am pretty sure that it is your EGR Valve that gets stock open... It sound pretty much like that.

It's a JDM motor. :(



Checking the head for warp is something that should be done when diagnosing to find out why a head to block seal failed, so a diagnosis of the head gasket is a broad thing, it doesn't necessarily mean the HG itself failed.

Again, I really hope not.



Thanks guys for all the suggestions. Tomorrow or Tuesday my dad and I are going to meet up with that mechanic and brainstorm. We're going to do some tests, like the comp test, fuel pressure, vacuum, and hopefully I can use his mutli-meter. Today mine told me that my distributor is giving almost zero resistance, which doesn't sound quite right. So either my distributor is completely fubar'd, or it's the multi-meter. Hopefully we'll learn quite a bit tomorrow.

85gtsblackman
08-11-2008, 04:50 AM
you may have a bad injector, or tps as well

Chris
08-13-2008, 02:49 PM
you may have a bad injector, or tps as well

We replaced the TPS, but if it was the injectors, wouldn't the problem be consistent throughout all the RPMs?

Apparently a guy on the MR2 boards suffered a similiar problem, except this his idled much better. His issue turned out to be the coil. I checked mine, but it isn't exactly in spec so that may be a problem.

But his had some of the same bogging until it go to the higher rpms, and it would give him trouble after 10 minutes of driving. If he let it cool down overnight, the motor would drive fine again until it warmed up.
Mine will drive for longer than 10 minute fine, but once I let it set after it warms up, that's when I get the problem.

Testing the car last night (trying to see if driving it pulled any more error codes), I was able to get a more detailed view of what the car is doing.

From idle to 2900 RPM, the car misfires and lacks some power, but it's not horrendous. From 2900 to 3400 the car bogs down, sputters (we've replaced the AFM, helped out a bit with this) and drives like utter shit. Once it hits the RPM band at about 3500-3800, the car, most of the time, smooths itself out perfectly and takes off. Misfire seems to go away, stops bogging, etc, etc. Runs perfect.

Whatever it is doesn't always occur this way, but it's usually pretty similar to that description.

I'm going to try bypassing the fuel pump relay and driving it to see if the relay may be an issue here.

The mechanic never got back to me or my dad about helping us out, so I'm going to have to try and source a fuel pressure tester, along with a vacuum leak tester and a compression tester. Or I'm going to have to shell out money for all of the above. Money isn't something I have very much of, so I'm kind of stuck when it comes to getting concrete results on those.

85gtsblackman
08-13-2008, 05:14 PM
autozone loan a tool ?

my camry did that come to think of it, replaced dizzy w/coil, car ran fine

Chris
08-13-2008, 05:40 PM
autozone loan a tool ?

my camry did that come to think of it, replaced dizzy w/coil, car ran fine


They might.

Did you have to replace the entire distributor?