I have a supra that is only running on the first and last cylinder. It was running poor and I pulled off the spark plug wires to see how it ran. After more testing I removed all 4 middle plug wires and it kept running the exact same. Any suggestions what would be causing this? The plugs and wires are new.
Do you have good compression on all cylinders?
Do you have good spark on all 6 wires . . . I’m talking an extremely bright blue spark using a spark tester. With all due respect to anybody possibly reading this, I don’t consider holding a spark plug against ground as a proper test. Opinions may vary, but you got mine
I don’t know what year Supra you have, but I’ll assume you have EFI . . . are all of the injectors working properly? I would use a noid light for this purpose, as that will tell you if they’re being properly pulsed
1 Like
Hmm, the plugs and wires are new. Did this problem arise right after replacing them? Wise mechanic say “always look first where the human was last”.
If you go backwards around the distributor starting from one, the #1 and the #6 plug wires will still be in the correct location but the rest will be wrong.
4 Likes
6cyl motor will run on 2 cylinders. Nice. Getting close to a perpetual motion machine. Only 2 more cyls to go.
Compression is not super but good enough to run decent. the highest is 130 lowest is 110. IN this order from first to last, 130, 120, 125, 120, 110, 120.
I consider those compression numbers to be quite low
Do you have hydraulic valve lash adjusters, or do you have to manually adjust the valve lash? I’m thinking buckets and shims, since this is a Toyota. If the latter, perhaps the valve lash is too tight, which would be normal as an engine ages. If it is way out of spec, I’d suggest adjusting it, and checking that compression again
You still haven’t gotten back to me, as to using the spark tester
I’ve seen plenty of weak ignition systems that were enough to barely fire the spark plug held against engine ground, but not nearly enough to fire the spark tester. I’m wondering if #1 and #6 are even getting a good spark?
You really need to have good spark, good fuel pressure and good compression
At least one of those is clearly not good, IMO
I am going to try a spark tester Monday when I get to the car. One guy who looked at it yesterday pulled one of the wires off the dist cap and almost knocked him on his butt from the spark.
As for the valve lash adjusters I don’t know. That is beyond my knowledge.
I did a fuel pressure test the summer of 2015 it was good and also vacuum pressure tested was good. Within the Haynes book recommendations.
Those compression tests were done the other day. I did compression tests also in the summer of 2015 and they came up on average. I did 3 test for each cylinder. 1 - 145 2 - 145 3 - 155 4 - 155 5 - 130 6 - 120.
Vacuum pressure? That’s an interesting concept.
1 Like
Even if those numbers are low, they are not low enough to cause a problem like this. Furthermore, the compression of cylinders #1 and #6 are not out of line with the rest of the cylinders.
What is special about 1 and 6? For one thing, they are a 360 degree pair that reach top dead center together. Cylinders 2 and 5 are another 360 degree pair and cylinders 3 and 4 are another 360 degree pair. That means that the wires that go to plugs 1 and 6 should be on opposite sides of the distributor. The wires that go to plugs 2 and 5 should be on opposite sides of the distributor, and the wires that go to plugs 3 and 4 should be on opposite sides of the distributor. If you swap the wires of any 360 degree pair, those plugs fire at the end of the exhaust stroke instead of at the end of the compression stroke and both of those cylinders won’t fire even though they are getting a strong spark.
2 Likes
So are you saying 4 of the wires may be in the wrong sides?
If you do the 1-5-3-6-2-4 firing sequence clockwise when it should be counterclockwise or vice versa and you start from the correct distributor terminal for cylinder number one, 1 and 6 will be correct but the rest will be wrong and their cylinders won’t fire even though they are getting a strong spark. It’s just something to check.
1 Like
In line 6 cylinders have the firing order 1-5-3-6-2-4 @B.L.E. V-6 engines use the firing order 1-2-3-4-5-6 , 1-6-5-4-3-2, or the Ford equivalant.
I think the 5MGE uses hydraulic lifters. When that engine debuted, I remember wishing my 1982 Cressida’s 5M engine had those. (BTW My Cressida’s valve adjustments are via lock-nuts- no shims)
I think OP has an extremely old Supra, with an inline 6
I also seem to remember something about dropping in a replacement engine . . . and the replacement engine was from a different model year, with no provisions for a knock sensor. I’m not sure if that was this guy, or somebody else
Yes db. I seem to have let that engine totally slip my mind. I actually thought that the 22R engine or a variant was still in the Celica/Supras at that time. And it is amazing that a 6 cylinder will run on 2 cylinders.
What’s the recent history for this car? Was the engine running ok, then for no reason you started it up one day and it was running poorly? Which you later discovered was b/c the middle 4 cylinders weren’t properly working? Or is this engine had major work done on it and has since then never run properly?
For a cylinder to work properly it needs 5 basics
- good spark
- at the right time
- proper amount of the correct fuel/air mixture
- good compression
- ability to expell the burned exhaust gasses
Seems unlikely to be 3 or 5 since those would generally affect all cylinders. You’d already proved 4 is unlikely. So that leaves either 1 or 2. Suggest to Focus on the ignition system. I presume this car uses a distributor cap w/electronic ignition module. So first thing to do would be to ohm out the high voltage wires between the cap and the spark plugs, then replace the cap and the ignition rotor, after that replace the ignition module.
Those compression numbers are way too low and it’s possible that low compression could be keeping it from starting.
You might try this. Remove all of the spark plugs, Add a tablespoon of oil to each cylinder. Reinstall the spark plugs and see if it will start and run. If it does then the engine is on its deathbed.
1 Like
The engine has never been running ok since I got it. A few years ago I changed the engine and have never got it running right. Recently I have got back to it.
I did a spark test with a spark tester on all 6. They all had great spark. I also put a stethoscope to all 6 fuel injectors and all 6 sounded nice and crisp. It could be a timing problem, but would it run on 2 cylinders if it was not timed very close? It could be a injector problem, but does the sound not tell me they should be working? One person suggested that perhaps the valves are not working properly. I have found someone to look at it cheap. If they cant get it running right they will not charge me hardly anything. I have enough things to do and winter is coming soon.
Have you done as the others suggested, and made sure your ignition wires are routed correctly, on the cap?
I believe the cap has a number next to each terminal . . . ?
Yes the wires are right. Yes the cap does have each number on it. It idles really nice which I would think if it was not on time or very close it would not idle at all on 2 cylinders.