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Looking for a little input on this, have tried everything I can think of to solve this issue. Previously had a lean condition on both banks and now have high negative trims. One bank is -7% LTFT at idle and the other is at -14%. Short term is fluctuating 2-3% positive alongside that. The trims become increasingly negative under load reaching nearly -20% The car idles very rough and sometimes feels like its going to stall. To my knowledge I’ve sealed all vacuum leaks and pumped smoke through the system with a DIY smoke machine. Have changed all vacuum lines and clamped them securely. Fitted new fuel injectors, this has given me a hard starting condition which goes away if I give the pump a chance to prime the fuel rail. Ive ordered a fuel pressure regulator but Im unsure if that’ll solve the problem. Can’t smell any fuel fumes, have tried unplugging different sensors. Swapped o2’s, cleaned the MAF with contact cleaner. Have replaced the evap solenoid, new spark plugs gapped to spec. New air filter months ago. Tried an idle relearn doing the key on key off method. Cleaned up my ground wires, tested coil resistance primary and secondary circuit, coils are worn but functional. Vehicle runs worse when hot, although its also running rough cold now. Camshaft or crankshaft position sensor fault maybe? Ive cleaned the idle control valve and installed new gaskets on the throttle body and manifold. Spark plugs have a black ring of carbon round the edges and biscuit coloured electrode.
Thanks again, Adam
It would appear that the engine is rich which is shown by the negative fuel trims as the computer tries to correct and bring it back to a stiochiometric ratio. This is reinforced by the black ring of carbon on the plugs, the rough idle which is worse when hot, a cold motor running better when richer and worse when hot.
Look for causes of richness in the cylinders
You say that one bank is trying to compensate more than the other – this gives some direction as to the location. You’ve ordered a fuel pressure regulator, but what was the fuel pressure. It’s interesting to read that the extra time taken to let the fuel pump prime the rail has an effect on starting, this should get to pressure almost instantly, again what was the fuel pressure??? It seems condradictory that it takes longer to prime the rail and then when it does the engine is rich. Is the return to the tank restricted/ blocked causing the pump to fight the blockage and then the rail pressure is high because it can’t release the excess to the tank??? – thus causing a higher pressure to injectors leading to a rich condition in turn causing fuel trims to go lean to correct the situation. Remember that pressure of a fuel is not the same thing as delivery of a fuel.
I get the impression that you don’t have a scope – I would like to see the firing lines on the plugs to see whcih cylinders are richer and which are leaner.
If it was a horse you could shoot it, as it’s a car just keep on making the payments !!!
Unfortunately I don’t have a scope or a fuel pressure guage. The car uses a non return fuel system and the regulator is in the fuel tank. I agree that I should be checking fuel pressure. To me it seemed logical to assume the pressure regulator may be letting the pressure drop back down. I was thinking high fuel pressure could be causing this issue, the new injectors are the exact same part number as the old. If its a pointer the old injectors were slightly lean at idle and rich under load. Bank 1 runs cylinders 1 and 4, bank 2 runs cylinders 2 and 3. Im not entirely sure why theyre running different. What would you recommend I do at this point?
Would something like this work with coil on plug?
In my opinion, coil on plug is not a factor here. I can’t see that it would make any diference to this situation – the sugestion of looking at the sparklines on a scope is that they show the effect of leaner and / or richer cylinder mixtures.
There are on some vehicles diaphram type units that operate vacuum lines/sensors and if you have one of these (remember I am speaking genericaly) here as I don’t know what vehicle you have. If you have a leak in the diaphram it is possilbe for fuel to pass into vacuum lines and then to intake manifold and then to causing a type of problem you have described. You can ‘suck and see’ on these diaphram units and see if they are vacuum tight – I guess that you will not be able to suck and much as the intake manifold but it does not require a gauge to find a leaking diaphram.
As you don’t have a scope or fuel pressure gauge and I’m assuming the fuel pressure regulator is not adjustable you have reached a sticking point. Even if the fuel regulator is adjustable you would still need a fuel pressure gauge to set the regulator. One can set a fuel pressure regulator on a ‘suck and see’ basis but it requires practice and experience, something that comes with hair in the nose and ears.
There has been a fair bit of use of the “B” word here (buy), can you get access to a mechanic who comes with hair in his nose and ears and tell him what you have done and get a quote to either fix the problem or scope the vehicle and steer you onto the next course of action. Finding a good mechanic takes research and networking with people you come into contact with.
Don’t go into the first shop you see and say “fix this”. Spend as much time on the search for a good mechanic as you have spent so far on the vehicle. Knowledge is Power and Power means control and you need very much to stay in control of this situation, so develope the Knowledge to deal with the problem. If you find a good mechanic who will talk with you rather than too you, it would be a good step on the track to fixing this situation. You are already on this journey and you have found this website, good luck.
I have number of scopes – but one the first I bought was a Hantek 8 chanel Analoge – Analyzer. In part I bought it because there are good intruction materials on Utube and it was cheap for what it could do. But in mu opinion you need to team it up with the Amp clamp, form memory there are two amp clamps, you git the one that suits your needs.
hhttps://www.ebay.co.uk/itm/Handheld-Digital-Oscilloscope-Automotive-8-Channels-Analog-Analyzer-Logic-Bag/123818624022?_trkparms=ispr%3D1&hash=item1cd42a4416:g:teEAAOSwYu1coC1~&enc=AQAEAAACYBPxNw%2BVj6nta7CKEs3N0qVJhxXosS%2Fe2xn0C9nxG8jRhE3e14HYAr0iZV2AnEtJ5Lpe93yEfcTHuJ%2FI4PZxb6XhkbPn0aUHX3y3x1OUQXr6roXd2rXhAGLlaqtuhJWQ1XHl6rBKGEToqyN0ivk6VMuSyY3owHlAV2wZUlmt2aZOEoUwoi3KvXckr9S50IXSjPdDlpy8EhwVmVZXoq0ebPwXWW%2BwJWTiuY3sMn%2Ffhhm%2F7p0Dm5T4rdEO6YrWW6hq5GOrEJE%2BYFo3jwHqLlSPJQoL77LBCTIIgPw7a4QyzCNPpxjuw0lNvtcPLHJJmPKEB%2F20BS08VmUDIqblj8W%2FXv0QGAuCWQNB1BiI%2F1c%2B0UFNhLnx2IzSGx2uqXkt0AJrDhy8tXEGq1goknXbeD6XLxigfG6%2FsxN0qRgLl3funkusyCunmy7Dy8WirpbWwE%2F6zKFyhPVXw1XoujAwKldIZrP3J1nqHCwegB5RCN9w2vnW974ma2HPUnj4Lns6a6IwVhLujMt9LwsWU6bI%2BakthXLb7bHqgHGvJ%2B6tk4Kq56yDYUwVYppxc9GZnW5knCpotx7B6wU0n0RLGfz7fqz2FhgJaIBjjVSrquqKFaLrhjIuSoM1Dke2x3Q1F77nmalmrXUjG3GZj4HEegXngqTEaodg5F4dL6dYtoksA93ERMg7uqdg7dJhUz3OSkcInGXDmRQ7nEx9pubtyeN5QltzyAbeCYXI%2Fjuo07bUtAEDK%2FMu3mYPVTFVZyfvdnAt0UrZ1JyzRg%2BSSjPN9WSsDIwSJq5mer3PU%2FFR2tW3Hs0x8it1&checksum=123818624022a6f014e2e8bf4861ace4a7dff060c28dave
Thankyou for your reply, the regulator is practically impossible to test without a fuel pressure guage in this vehicle, unfortunately the regulator isn’t driven by a vacuum line either, rather part of the fuel pump assembly. I know disconnecting the line would have been the obvious move if the FPR was driven by vacuum though, have tried blocking EVAP off to see if it was drawing extra fuel in there, no change. Even unplugging various sensors made no difference. I’ve checked MAF resistance as per the workshop manual. It appears to be in spec also. I’ll check out the scope you’ve linked me to. In the mean time I’ll have a look for a good mechanic. I know of an auto electrician but I’m not sure if this is something he would deal with.
Just a thought, take out the Air cleaner Filter Element – could it be possible that your Air cleaner is Blocked/Dirty and retricting air flow.
I could give it a go dude. Unless the MAF could be over reporting? The trims get increasingly negative with higher engine RPM. I’ll try it without the filter to see what happens.
The air filter housing does have a chip in it above the filter. Although I didn’t think much of it given it’s before the MAF. I’ve some automotive clay laying about I could plug it with to test.
You say that you cleaned the MAF with ‘contact cleaner’. I’m unsure of what that is, but regardless, did you check the MAF before you cleaned it and again after. The ‘crime site’ of any fault can give you as much information before you touch anything as after you have done something. It’s too late now to take measurements of before but it should be reporting within OEM parameters now that it has been cleaned.
A dirty MAF will show a voltage that can be different from the specified voltage – this could be the problem, remember I am talking generically here I don’t know what your vehile is but the effect is the same, an the effect of a dirty/missreporting MAF would give you the symptoms you decribe.Again speaking generically, the ‘chip?’ in your air cleaner could be an ambient temerature sensor – again there are tests that apply to this – I do say to you that BEFORE you do anything to it, to check out its current operating reporting against the specifications for your vehicle.
If you do find that it is the MAF and you correct this, remember that the Long Term Fuel Trims will take some time to adjust to the new imformation of the MAF. Add Long Term Fuel Trims to Short Term Fuel Trims for a total Fuel Trim figure before and after the engine settles down/warms to operating temperature.
Knowledge is Power and Power means Control.
The chip in the airbox housing, I meant a piece is chipped off. I tried running it today without the filter or any obstructions and it made 0 difference to my trims. Have ordered an endoscope to check inside the manifold. I’ve read that the divider can sometimes collapse inside these plastic manifolds. A camera seems a sensible idea to check where I can’t see. Air temp sensor is built into the MAF on this vehicle. And thats what I was questioning, is the MAF actually over reporting. Perhaps pick one up from the scrapyard for cheap and check it with that. Whats throwing me off is the way both banks are affected differently. The MAF seemed to be reporting a higher reading after cleaning. Contact cleaner is electronic safe, it’s for cleaning corroded contacts up. Although I also discovered it appears to be MAF safe. I do have an offbrand MAF installed and no longer have the original one. Have to see if I find anything with the endoscope, although im skeptical, manifold blockage is something I’ve overlooked. I’ll take notes before and after a different MAF
Could an exhaust blockage cause rich trims by some chance? The manifold has 2 precats in it. I was going to do an exhaust back pressure test tomorrow.
OK, so we know the air filter is not influencing the fuel trims, so I feel confident that this can be ticked off, as we move into the engine we get to the MAF………….
Can you hook up a DVOM to the MAF and take some readings – at KOEOFF KOEON then at idle and next see what happens at WOT (Wide Open Throttle). I just have a feeling that you could be right about the MAF over reporting, I have an aversion to spending money on parts until I am absolutley sure that I am replacing a dud part.
Re you looking for a broken baffle inside the intake manifold, its possible but I would think that if it broke internally there would be a permanent and definited influence to one or more cylinders. I remember years ago a Diesel Truck had a loss of Power when it was opened up under load/high speed, much was tried and eventually it was found to be a bit of the air intake trunking flapping shut when the air flow was high then springing back into place when the load was off. If the exhaust was strangled it would most likely be in the cat which would show in the post cat O2 sensor. The exhaust backpressure should be almost nothing (measured before the cat and maybe less after the cat). If you have a compound pressure gauge well and good, in years past we used to drill a tiny hole in the pipe to see what the leakage was. With a blocked or partially blocked muffler it used to hiss out as if it was an air compressor. No backpressure gauges in those days. Then we sould repair the hole with a self tapping screw. Ah those were the days, one could stand on the footpath and diagnose cars as they drove past.
Google: Symtoms of a Blocked Catalytic Converter – I don’t think that this your trouble, but Knowledge is Power etc.
So I ran an exhaust back pressure test and found no restrictions. However I did resolve the fault eventually. It turns out the previous fuel injectors had contaminated the oil with fuel and pushed it well over the fill line. New oil and filter and the negative trims are gone. However the engines now running a tad lean. Am gonna chuck some water over it and find the leak, it appears my smoke tester isn’t gonna find it. I can’t believe I’d overlooked something like this.
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