Intermittent misfire

[Suprasonic19]

I stumbled upon the diagnosis flow chart for occasional stalling (http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=15) and it shows afm after codes. Well I checked codes and nothing but code 51 when its in any gear other than park or neutral, even not touching the gas. As soon as you put it back into park or neutral flashes no codes. So i checked the afm as per tsrm (http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=96) and found odd readings and could use some interpretation.

With meter set to 200k ohms I got OL both ways with Ks and E1. Vc to E1 got 156.2 and E1 to Vc got 155.9. THA to E2 was at 3.8. All these were taken at 50 degrees. I brought the afm inside and put it in the bathroom with the heater on for awhile with a temp gauge in the room and got it up to 70 degrees. Rechecked every thing and all readings were the same except THA to E2 was now 2.7.

So it seems THA and E2 are good but all the others are well beyond specs. Should I find a replacement afm or am I misreading this?

 

[jetjock]

Without an afm code you ought not to be messing with it. Nor should you be worried about the 51 because it's supposed to work that way...

 

[Suprasonic19]

Thats what I originally thought also...but the other day I had a car in the shop for almost the same condition I have just not as consistent and it ended up being a bad afm. With the scanner hooked up I watched the isc voltage, all 4 o2 sensors, idle speed, and a/f values and most the time everything would look great but then suddenly the afm volts would drop, then o2s would show a lean condition, then the isc would go up and down trying to compensate. The car usually would stall after about 6 seconds of this happening, after I restarted it it would be fine for a couple minutes then itd do the same thing. Replaced the afm, runs perfect. The interesting thing was, the entire time I was with the car it never threw a code. No history codes either. The afm wasn't necessarily bad...just not working properly. Thats why I decided to test mine even thought it doesn't have a code for it.

 

[jetjock]

Apples to oranges. One is analog while the other is digital. You're almost surely barking up the wrong tree, Not that it can't fail but you sure aren't going to find out using an ohmmeter.

 

[Suprasonic19]

What is the proper tool to test an afm with?

 

[jetjock]

Huh? Didn't you just say you worked in a shop?

 

[Suprasonic19]

Yes I do, but Ive been wrong before, and I'm here to learn. You said I wont be able to find out if my afm is bad with an ohmmeter, so what do you recommend I use? The tsrm says an ohmmeter (analog type) but I assumed a digital one would work just as well. Is there a reason the tsrm specifically says analog type?

 

[3p141592654]

An oscilloscope, or a DVM that can measure frequency would be useful for this AFM.

 

[mk3supra978]

i wiggled my fuel injector wires and it was loose tighten those up and the misfiring sound went away kinda sounded like your video you posted check those out man

 

[Nick M]

The tsrm says an ohmmeter (analog type) but I assumed a digital one would work just as well. Is there a reason the tsrm specifically says analog type?

Toyota published a lot of technical misinformation through the years that I have seen. I suppose it is translation errors.

 

[3p141592654]

In the 80s, digital meters often had very slow sample rates, and would miss fast transients, that is probably why they recommended an analog meter. 25 years later it doesn't make sense, any decent DVM includes a high speed signal bar or other analog like indicator.

 

[Suprasonic19]

i wiggled my fuel injector wires and it was loose tighten those up and the misfiring sound went away kinda sounded like your video you posted check those out man

Ive checked those several times and they are definitely good and tight.

Toyota published a lot of technical misinformation through the years that I have seen. I suppose it is translation errors.

Funny you mention this because just tonight I found on page 58 of the fuel injection system chapter it says under inspect fuel pressure "(a) Check that battery voltage is above 11 bolts." I had no idea battery voltage was rated in an amount of bolts back in the 80s.

 

[Suprasonic19]

Today I finally got a hold of a fuel pressure tester. Here is my testing procedures and what I found.

Battery voltage at 12.8 before testing. Engine cool but not cold. Roughly 100 degree coolant temp.
1.Hooked up gauge at cold start injector fitting on fuel rail.
2.Turned key on-0 psi. Put jumper wire between +B and Fp in diag plug, pressure instantly jumped to 42psi and could hear rushing of fuel in rail and lines.
3.Removed jumper wire and pressure faded to 38psi.
4.Started engine pressure jumped to 45psi while cranking then faded to 32psi after engine started.
5.Every time the engine misfired/strained, pressure would raise to 34 then back to 32 after each miss.
6.Disconnected vacuum hose from pressure regulator and plug line with my thumb. Psi went up to 41 and stayed constant even with misfires.
7.Reconnected vacuum line and pressure fades back to 32 and continues to raise to 34 with each miss.
8.When revving engine psi jumps to 40 then levels back to 32 as soon as I would hold an rpm no matter how high or low the rpm. After Id let go of the throttle the psi drops to 30 then returns to 32.
9.As soon as I turn the key to off, pressure raises to 40 with in a second or two, then Id hear a click from under passenger side dash and the pressure would lower to 38 and would stay there for several minutes. After 10 minutes the pressure had lowered to 36. After 2 hours the pressure had lowered to 25psi.

Just a side not, I had to get the car smogged a few weeks ago and it passed. Just an fyi.

 

[Suprasonic19]

Also while doing this test I discovered a severed wire.

This is looking under the upper intake manifold. There is some slight blacking on the mani as if its shorting on it. Ill be repairing this this weekend but my question was, anyone have any idea as of what this wire may be? I followed most the harness and checked all the sensors(cps, temps, iac, tps, injectors, etc.) and couldnt find any solid brown wire.

 

[3p141592654]

That all sounds normal. Your fuel pressure is tracking engine manifold vacuum, that is why it is varying the way you noted.

 

[Suprasonic19]

Well all the readings were high, not much more than factory specs but tsrm says if pressure is high replace fuel dampener valve. So im going to look more into that.

 

[KTM530]

I could be wrong, but you broken wire looks like a knock sensor wire, has someone fixed this alreaghty?

 

[Nick M]

A little big higher fuel pressure dosn't cause a misfire.

 

[Suprasonic19]

Just wanted to pull this back to the top. I finally got my turbo back on and am revisiting the misfire problem. While the turbo was off I pulled the intake manifold and went over all the vacuum lines and connections and also to figure out the broken brown wire was. While doing that I found out the dealership wired in new knock sensors and wiring all the way to the ecu and did cut the old wire back or remove it. Post number 34 in my build thread- http://www.supramania.com/forums/showthread.php?101797-88-7MGTE-White-Pearl-Targa-Lots-of-Pics/page4 .Found many more split vacuum lines, so i replaced almost every single vacuum line I found, except ones I had already replaced but I still inspected those. finally replaced the crankcase to valve cover vent hose, got it from DM.


I went over all my intake and intercooler piping, did not find any leaks tears or any other concerns. I installed a known good fuel pressure dampener as the tsrm recommend replacing this if the fuel pressure was high which it was slightly high. After all this was done and I started the motor for the first time the miss came right back just as before. Exact same symptoms and everything. Which further leads me to believe its electrical and/or fuel.
Ive noticed the exhaust does smell rich especially when its missing alot. Yesterday I went out to dinner, was in the restaurant for a little over an hour, came out, and cranked the car. It was still hot as the outside temp was about 85 and the came stumbled to live. Didnt fire right up like normal. And as soon as it fired it died. So I cranked it again but just barely popped the throttle, it fired right up and went into high idle(1200 rpm aprox.) then slowly settled back down to normal idle(650 to 750) then started misfiring as usual. Almost immediately after it started I could smell the exhaust fumes and they smelled extremely rich. As if I was breathing straight from a gas pump.

Saturday night after I took it for the first test drive I pulled the plugs. First thing I noticed...oil in the galleries again, a small amount, but it is there.



After cleaning this and pulling the plugs I found that they all had a gap of .028in which doesnt make sense because when I installed them a thousand or so miles ago I gapped them to .031 like factory spec. I also found 5 out of 6 had black burn marks around the bottom of the ceramic. Ones like when the exhaust is escaping up through the seal of the plug. I found number four plug had a huge crack up the ceramic. These plugs are only a thousand miles old..why would they be so torn up already? Also can anyone interpret the plug tips as to what my engine is doing?



Note the large crack on number 4




I decided to try a different type of plug, figured maybe my engine isnt liking the platinum. Got the exact same type of plug just in the v-power not the lazer platinums. Gapped them to .031 in and cleaned out the galleries and plug wire tips. Installed and didnt change a thing. If anything the car feels a little sluggish taking off from a light now. Probably go back to platinums but for only 20 bucks I figured hell might as well give it a shot.

Since the car has been running again Ive noticed a whine from my alternator, and when its cold the bearings squeal, Ive got a reman one coming in tomaro. Also related, things seem to put a heavy load on the alt. Headlights dim significantly when I hit both window switches, headlights dont seem very bright either. Ill test it before I replace it just so I have specs to base off of.

So, after all this now Im on to the coil packs, Im going to test them and see what I find.

 

[Suprasonic19]

Well tonight I can finally bring an end to this very long and frustrating chase. I installed the new alternator and tested the coils, coils were good and the alt didnt change much but my lights are much brighter and it doesnt load down as much. I got ahold of a test light today and checked my timing just to rule it out before i replaced the fuel pump. And to my surprise the timing was at 25degrees btdc. I adjusted the cps as far as the range would go and one side brought it down to about 23 and the other way went up to 40. So i set the motor to tdc, pulled the upper timing cover and inspected the timing belt and alignment. All three cam/crank relations were perfect and the belt was in good shape and not loose. I then pulled the cps out and sure enough, it was about three teeth off counterclockwise. As in 3 teeth to the left if you are looking into the cps hole. I cleaned and inspected the cps, all looked good so I realigned it to the tsrm(drill mark inline with the notch on the cps housing) and installed with the retaining bolt right in the middle of the range. Put everything back together and cranked it over. The engine fired right up, no stumbling or shuddering or hesitation like usual so i knew something was better. I let it get back up to op temp and there wasn't a single miss. It was running a little high(800-900 rpms) Put the timing light back on it and it was at 15 degree btdc, rotated the cps clockwise just a smudge and brought it back down to 10 degrees. All of this was done with terminals T and E1 jumped with a wire. I locked down the bolt and pulled the jumper and the timing went up to 13degrees as per the tsrm. Went for a nice spirited drive and I was speechless how well she performed. Cant even say how great it felt to finally get this miss figured out. Thank you to all who helped and gave me advice. Until the next problem arises as I am never completely done with my supra.