Mysterious Illness of my 7m.....

[schmall's supe]

Allright so my 7mgte 89 is all together after the bhg job now the car will crank start but not continue running without gas it will immedaitly die with out throttle. Now between 1500 rpms and anthing higher itll sound smooth anything lower and it will begin to miss and die under 700rpms. Now right around 1000 rpms it will backfire but through the intake manifold not the exhaust. It sounds as if gas is exploding beacasue of heat through the intake manifold. It seems ive got everything wired up correctly and it was throwing codes 52 which is knock sensors i believe and also at one point code 12 which is loss of power or intermiitent power to the ecu. i switched the ecu's and the problem continued both codes and the strange backfiring (frontfiring more like) also the tps cps idle speed sensor afm are all in good shape and working properly. My next step is to change up the igniter i thought maybe the wires to coilpacks could of been crossed and was causing this but no its not. SO and of now the problem remians mysterious.

Any help advice or ideas would be much appreciated thank you.

pat

 

[schmall's supe]

oh yea duh the timing is right on point too at about 12 degrees before tdc

 

[Rennat]

are you sure your timing is right... if your "backfiring" through the intake manifold than your intake valves are opening during the combustion stroke... sounds like you dont have the cams right...

 

[wingman]

i'll chime in on this one, i spent all of yesterday trying to figure this out. the engine seems to catch itself every half second or so and try to stay alive, but it's a consistent pattern and not a "die whenever you want to" situation.

mechanical timing is spot on, intake and exhaust cam timing marks are lined up on TDC
electrical timing has been gone over several times, CPS re-installed by the book...timing is fairly consistent considering how the car is running, around 10* or so if i remember right. My thought on this is the cam sprocket may be mistimed to the cam itself, but this seems really unlikely.

had code 11, checked power/ground circuits, cleared it out, never popped up again.

code 12 was thrown because of a shorting CPS wire, that was addressed with no change in engine performance

code 52 popped up during the intake backfires, no other time, and not every time the car was started

no other codes were thrown

coilpack resistances are all ok, there is power to all 3 coils, the coilpack wiring at the 4-wire connector was re-done and I thought that may have been the problem, but apparently not.

voltages at the ECU are all good (KOEO), power to all sensors, continuity to ground everywhere there should be. sensor voltages at ECU weren't checked with the engine running

one other thing I noticed was when holding the gas steady to where it would barely keep alive, it would slowly creep up in RPM, then take off to 3-4 grand with no change in throttle position. TPS is adjusted correct, IDL contact opens/closes like it should, and voltage range is good.

 

[IwantMKIII]

sure you spark plug wires are properly installed to the right cylander and corresponding coil pack? I would definately look there if the timing really is done correctly, other than that i'd look again into the CPS and ignitor

 

[schmall's supe]

yeqa most definatly the cams are on right position and we got the coilpacks wires hooked up too i believe we went through all the combonations and there spot on but were still lost.

ohh wingman your nathan right?

 

[wingman]

yeqa most definatly the cams are on right position and we got the coilpacks wires hooked up too i believe we went through all the combonations and there spot on but were still lost.

ohh wingman your nathan right?

yeah that's me.

just a heads up guys, all the obvious stupid stuff has been looked at already. plug wires were all checked, every underhood connector was taken apart, pins inspected, and put back together. the vortex screen is in the AFM, all vacuum lines/components have been looked over. Timing has been checked and rechecked on both mechanical and electrical end, basically nearly every little "gotcha" gremlin has been eliminated.

the only things that have not been tested are the vortex signal from the AFM (need a scope for that one), MAP, and igniter. fuel pressure is the last mechanical thing yet to be checked, but I highly doubt that would cause problems of this degree.

 

[IwantMKIII]

^well man we just have to cover all the basics.

As long as everything is mechanically sound it will really only be in a few places, CPS, ECU, Ignitor, AFM. AFM won't really cause problems like this that im aware of or ever heard of, usually if its bad it won't run at all or your AFR's would be going nuts. I might be possible that some of the wires on the ignitor or cps got crossed (SOMEHOW). Also check your grounds, not properly grounded components can do some really crazy things to a car.

 

[88supraFAST1]

I would add a few more grounds, if you say everything is right it only sounds to be to be an electrical problem, put some more grounds in from the engine to the engine bay, also check for vacuum leaks. i have seen it time and time again of a car running like shit because of vacuum leaks.

EDIT: Just because you cam timing is on doesn't mean your crank isn't off a tooth i would check that to.

 

[Shima]

i had a problem like this first off my intake manifold wasnt on properly leaking air causing the rmp jump on the throttle then i had smoke and blow back which i thought was from around the back of the engine just turns out 1 of my spark plugs were cracked slightly

this bugged me for at least a week untill i realised what the problem was. try checking the plugs or spraying some wd40 around the seals see if any air is escaping

 

[schmall's supe]

alright thanks guys ill check it out

 

[GrimJack]

AFM is easy to eliminate, the car will start and idle fine without it.

 

[schmall's supe]

is it possible that maybe the machine shop who did the valve job and resurfacing of my head could be to blame maybe they screwed up some of the intake valves by any chance??

 

[IJ.]

Check the valve lash.

 

[schmall's supe]

which is that gaps between the cam lobes and shims? prolly wrong what is valve lash

 

[3p141592654]

Running lean at low speed because of a big air leak might cause this. All vac lines okay? EGR connected properly to surge tank? Brake booster connected?

 

[schmall's supe]

yeaa all those aspects checked and double checked cept maybe the egr but it wouldnt cause problems of this magnitude or would it ??? and valve las is form the shim to cam lobe right?

 

[noah89t]

without having read too much of this. my car was not idling on its own last month and i played hell figuring out what it was, i sprayed some carb cleaner on the 1,2-3,4 runners on the upper plenum and the car would idle higher, so i pulled it off and the intake mani and found about a 2 inch section of gasket missing. put on all new gaskets and now it idles fine.

 

[schmall's supe]

hmm ill check out the plenum might be my prob

 

[3p141592654]

Since it won't idle, any leak is going to be huge!