HiC wrote:
> '89 Toyota Supra with a 7MGE with less than 5K since a rebuild.
> Recently it's developed an odd problem. Starts fine and runs smooth at
> first, but after it's been running approximately 20 minutes or so it
> develops a miss as if on one cylinder. Turn it off for a few minutes
> and it's okay for a bit but then starts doing it again.
>
> Could a plug wire be causing this? Or does it sound like something
> else?
>
> Thanks
>
Do you mean the miss is like it's running on one cylinder or affecting
one cylinder? It could be many things, but what you are describing
sounds like a component that is failing due to heat. It may be a plug wire.

When it's missing, try pulling off a plug wire one at a time to try and
isolate the cylinder. Then swap two wires and see if the affected
cylinder follows the wire change.

Did you replace all the secondary electrical components ( plugs, wires,
ect) after the rebuild?

"HiC" <brassplyer@yahoo.com> wrote in message
news:7fd20fe2-2c0d-434c-b840-cb4b880a1be1@e23g2000prf.googlegroups.com...
On Jan 25, 1:09 pm, "Ph@Boy" <u...@example.net> wrote:

> Do you mean the miss is like it's running on one cylinder or affecting
> one cylinder?


The latter.


> It could be many things, but what you are describing
> sounds like a component that is failing due to heat. It may be a plug
> wire.
>
> When it's missing, try pulling off a plug wire one at a time to try and
> isolate the cylinder. Then swap two wires and see if the affected
> cylinder follows the wire change.
>
> Did you replace all the secondary electrical components ( plugs, wires,
> ect) after the rebuild?


It seems to be the #1 cylinder - i.e. that's the one that makes little
or no difference when the wire is disconnected. I replaced the cap/
rotor, a new plug and wire in that cylinder makes no difference.

Possibly an injector that's having issues?
****************

If you can, try swapping the spark plug and wire from anothe cylinder and
see if the miss changes to the other cylinder. If swapping makes no
difference, check the wiring to the injector and make sure the wire harness
is secured. If the wire is tight, get your manual out for the procedure for
checking injectors. Before you go and try swapping injectors, try a bottle
of Chevron Techron fuel injector cleaner, and if you do end up removing an
injector, get replacement gaskets beforehand.
--

Ray O
(correct punctuation to reply)

On Fri, 25 Jan 2008 23:32:56 -0600, Ray O wrote:

> If you can, try swapping the spark plug and wire from anothe cylinder and
> see if the miss changes to the other cylinder.


I would suggest the #3 or #4 plug...

Ph@Boy wrote:
> HiC wrote:
>> '89 Toyota Supra with a 7MGE with less than 5K since a rebuild.
>> Recently it's developed an odd problem. Starts fine and runs smooth at
>> first, but after it's been running approximately 20 minutes or so it
>> develops a miss as if on one cylinder. Turn it off for a few minutes
>> and it's okay for a bit but then starts doing it again.
>>
>> Could a plug wire be causing this? Or does it sound like something
>> else?
>>
>> Thanks
>>
> Do you mean the miss is like it's running on one cylinder or affecting
> one cylinder? It could be many things, but what you are describing
> sounds like a component that is failing due to heat. It may be a plug wire.
>
> When it's missing, try pulling off a plug wire one at a time to try and
> isolate the cylinder. Then swap two wires and see if the affected
> cylinder follows the wire change.
>
> Did you replace all the secondary electrical components ( plugs, wires,
> ect) after the rebuild?
After you have done what Ray, Hachi, and myself have suggested and still
are having problems, it may be a mechanical problem and do a compression
test, and or leak down test.

It may be something as simple as a re torque of the cylinder head bolts,
or a bad cylinder head gasket, or maybe the person who did the rebuild
put a ring on upside down by mistake, possibly a defective ring, or
wrong piston clearance. Perhaps a leaky valve. Just some thoughts.

HiC wrote:
> On Jan 25, 1:09 pm, "Ph@Boy" <u...@example.net> wrote:
>
>> Do you mean the miss is like it's running on one cylinder or affecting
>> one cylinder?
>
>
> The latter.
>
>
>> It could be many things, but what you are describing
>> sounds like a component that is failing due to heat. It may be a plug wire.
>>
>> When it's missing, try pulling off a plug wire one at a time to try and
>> isolate the cylinder. Then swap two wires and see if the affected
>> cylinder follows the wire change.
>>
>> Did you replace all the secondary electrical components ( plugs, wires,
>> ect) after the rebuild?
>
>
> It seems to be the #1 cylinder - i.e. that's the one that makes little
> or no difference when the wire is disconnected. I replaced the cap/
> rotor, a new plug and wire in that cylinder makes no difference.
>
> Possibly an injector that's having issues?
>
>
After you have done what Ray, Hachi, and myself have suggested and still
are having problems, it may be a mechanical problem and do a compression
test, and or leak down test.

It may be something as simple as a re torque of the cylinder head bolts,
or a bad cylinder head gasket, or maybe the person who did the rebuild
put a ring on upside down by mistake, possibly a defective ring, or
wrong piston clearance. Perhaps a leaky valve. Just some thoughts.

On Jan 26, 7:55*am, "Ph@Boy" <u...@example.net> wrote:

> After you have done what Ray, Hachi, and myself have suggested and still
> are having problems, it may be a mechanical problem and do a compression
> test, and or leak down test.


I believe I found the culprit. The plastic fitting for the injector
electrical connection has just about completely disintegrated and the
plug for the #1 injector was basically only very loosely laying in
proximity to the pins on the injector.

What I think was happening was that it was *barely* making a
connection and as the engine heated up the rigidity of the wire bundle
changed and it broke the tenuous contact that was being made. I'm
actally surprised it was working at all. Once I shoved the plug into
the injector, there's enough tension from the rubber seal to hold it
in place but I definitely need to look into doing something about
those plug ends.

In one previous scouring of area junk yards I didn't even find one car
with a 7MGE engine. I'm hoping I find that the connectors on other
Toyota injectors I can find in salvage yards are the same
configuration - OF COURSE they won't be.

Maybe I'll home-fabricate something using JB Kwik or some other mold-
it-yourself epoxy. Besides the expense of a new wiring harness for
that car, I don't look forward to the PIA job of replacing it even a
little bit, so I'm all for jury-rigged but functional measures.

"HiC" <brassplyer@yahoo.com> wrote in message
news:b90699ee-81c2-4486-9cd5-b18399e1ebb2@b2g2000hsg.googlegroups.com...
On Jan 26, 7:55 am, "Ph@Boy" <u...@example.net> wrote:

> After you have done what Ray, Hachi, and myself have suggested and still
> are having problems, it may be a mechanical problem and do a compression
> test, and or leak down test.


I believe I found the culprit. The plastic fitting for the injector
electrical connection has just about completely disintegrated and the
plug for the #1 injector was basically only very loosely laying in
proximity to the pins on the injector.

What I think was happening was that it was *barely* making a
connection and as the engine heated up the rigidity of the wire bundle
changed and it broke the tenuous contact that was being made. I'm
actally surprised it was working at all. Once I shoved the plug into
the injector, there's enough tension from the rubber seal to hold it
in place but I definitely need to look into doing something about
those plug ends.

In one previous scouring of area junk yards I didn't even find one car
with a 7MGE engine. I'm hoping I find that the connectors on other
Toyota injectors I can find in salvage yards are the same
configuration - OF COURSE they won't be.

Maybe I'll home-fabricate something using JB Kwik or some other mold-
it-yourself epoxy. Besides the expense of a new wiring harness for
that car, I don't look forward to the PIA job of replacing it even a
little bit, so I'm all for jury-rigged but functional measures.

**********
If you can get at least the engine compartment end of the wiring harness,
you can splice a good connector in to the harness in your car. When
splicing, solder the wires and seal with heat shrink tubing and a dab of
silicone caulk or RTV sealant. Besides Supras, Cressidas also had 7MGE
engines.
--

Ray O
(correct punctuation to reply)