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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / January 2008Possible cause of miss as '89 Supra warms up?
'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 > '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 [quoted text clipped - 6 lines] > > 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? > 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. [quoted text clipped - 5 lines] > 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? 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 [quoted text clipped - 6 lines] > 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.  SignatureRay O (correct punctuation to reply) > 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... ;) >> Do you mean the miss is like it's running on one cylinder or affecting >> one cylinder? [quoted text clipped - 16 lines] > > 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. >> '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 [quoted text clipped - 17 lines] > 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. > 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. 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. SignatureRay O (correct punctuation to reply) |
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