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I had forgotten all about this one, but something has occurred to me – if your filter is PARTIALY blocked at the pump ( or if there is a PARTIAL obstruction in the fuel delivery system ) The pump can get the fuel system up to pressure but as the fuel is used from the delivery side of the obstruction, the pump can only gradually replace the fuel used. Look for the pressure building back up when you let it idle.
Thinking this through a bit further, as the fuel pressure drops and the engine injectors are being ‘starved’ the computer will compensate for this by extending the time length of the injector open. I’ve re read your original post about the fuel pressure dropping and this seems to ‘fit the bill’
To see this in real life, take the garden hose and just turn it on a fraction and watch the pressure build up slowly, when you let the pressure go at the other end it’s good for a bit and then the pressure drops to match the delivery rate.
Back to your car, look for somewhere the car has been jacked up and the jack lifting pad has crushed a fuel line, remember never give up you will get it fixed in the end.
Sounds like your fuel pump is marginal, good enough to keep with fuel requirements at idle, lbut an increased load sees it falling behind down to 43lbs. My feeling is that regulator would be at fault at any engine RPM, this feels like a volume supply issue. If you set a steady 3000RPM without drivning it, the fuel pressure should decay, but bear in mind that high revs in neutral do not use as much fuel as under load.
Without using the “B” word, could you swap the O2 sensors to oposing banks and see if the trouble migrates and follows the sensor – cost nothing and might be a pathway to future investigation. You will need a dedicated socket to fit the O2 sensors, but these days you really have to ahve one anyway.
Did you reduce the oil level? – It was interesting that it was high enough to fire a warning, that would not happen if it was just a little bit up. Theoretically it would be high enough for one of the rotating parts in the crankcase to hit the surface of the oil and explode oil everywhere including the cylinder walls, beyond the capacity of the oil rings to cope. I’ve never heard of anyone filling the sump that high but …………..
Many years ago there was an engine with A sloping cylinder that had a persistant problem with the internal flywheel spinning oil up into the cylinder – caused problems. Won’t cost any financial paid to correct the oil level and see what happens. Might take a little while for the rich situation to correct.I would think that a little oil on plugs threads comes under the ‘would’nt help’ category, but you can’t remember which ones so disregard this. If you find them clean up and see if it comes back.
After trying the water trick we can move onto signal strength from the Crankshaft Position Sensor but thats another story and may not be required, along with hydraulic lifters to the valves.Smoke and mirrors, er I mean scanners, are good and I am not decrying them. For now stay lo tech and try the water trick. I keep comming back to it (missfire) being on two cylinders that come on song when the revs increase.
Staying with the Lo Tech, have you tried moving first the Coil on Plugs to different cylinders and putting known good cylinder’s COP’s to numbers 2 and 8? Does the trouble move to other cylinders or does it stay with numbers 2 and 8. Only move the COPs not the plugs at the first test – you need to know if it is coils or plugs and moving both at the same time is going to be too much information.If moving the COPs around does not move the missfire, repeat and move the plugs around and try again. Knowledge is power and power means control – the above will add to the knowledge and you can move on from there.
If we know what the foregoing does to the problem we are a step closer to fixing it, and, still hav’nt used the “B” word.OH,……………. it is amazing what a chance remark can have in the course of events, the fact that it only occurs at idle pretty much negates everything I said in my previous comment. Get the garden hose, put it on a trickle flow – run the motor and run the water flow around all items that are connected to the cars vacuum intake. Keep the water away from electrical items and your hands away from the fans …. you are looking for a small vacuum leak that is so small that it is overridden by an increase in RPMs and an increase in the vacuum.
Don’t forget the Brake Booster pipe – and Brake Boosters can have an internal leak, this can be checked by dissconecting the pipe and blocking it – if the trouble goes away the leak is inside the booster…This is not guaranteed to find your problem but is a good starting point, low tech and does not mean the use of the “B” word. (BUY)…………….. WHEN you have done this let the motor run for while to thoroughly dry out the engine. I’m not a fan of riding ’em hard and putting ’em away wet!
I have never seen a 2005 Chevy Suburban, but does you engine have a waste spark type system? Now people will say that as it has Coil On Plug that is does not, but be careful with that one. Can you scan the Crankshaft Position Sensor and synchronise those pulses with No1 and see how many “trigger points” there are, there does not have to be a separate pulse for each and every cylinder. However all pulses should be of equal value or strength. It can be that 4 trigger pulses will do for 8 cylinders. I do not have the time to do this but you could go through the firing order and work it through, but it’s easy to make a mistake……………it’s relevant to something that 2 and 8 mostly missfire, and the rest of the horses are pulling their weight.
IF your scanner is Bidirectional, you can shut off each cylinder in turn and measure the RPM drops each time, could be a pair of lazy cylinders, but I think you would have found them earlier. When I was a child we used to talk about a “V8 beat”, this of course was an urban myth and a good V8 was as smooth as could be when all cylinders worked in harmony.And so back to the missfire – you say you have a missfire OK, is it spark related or injector related ???. In other words what is the root cause of the missfire. Having sorted that out, which cylinder?. Back in the day we could find a problem by starting a cold engine and running it for a few seconds and finding which exhaust manifold port was the coolest, this was a pretty cool way of finding a problem area. Back in the present we have Infra Red Heat Guns and put the red dot on any part of the engine to get a far more accurate result. Your random missfire would I feel have to be pretty constant and on one cylinder only for this to be of any use to you here.
I think it come back to the first sentence – is it spark or injector related.
My feeling is that the focus has moved from the missfire to the blip, the immediate problem being the missfire, keep the problem in the front. From memory Auto Enginuity can count missfires and their source, when you say “random” missfire, are you talking about a missfire from any cylinder or one particular cylinder. If any cylinder it could be from the CKP sensor or if from a particular cylinder it could be in the area of a paticular ignition coil.
I’m not saying the it is the ignition coil for example but something that relates to that particular part of the system that makes the ignition coil working in harmony with the rest of the engine.
You say that the blip occurs accross ALL sensors and that they drop to zero for a second and return to normal.
In my opinion you are looking for a “common to all” fault. Look and the ground side of the electrical system, start with the battery and move onwards to chassis and block grounds and don’t forget the ECM ground as you obviously have enough power to crank and start, but you could still have a poor ground to the ECM.You can do this by eye and with the multimeter, then check power feed to the fuses box and then to the fuses to the ECM (engine control module/ computer).
Something I assumed, and I should not have – – does the blip coincide with the missfire. A different senario, but you have enough to go on with at present, if the above does not help come back and let us know how you get on, I still feel that what you said about the blip occurring across all sensors is significant.
DO NOT DRIVE THE CAR – Whatever it is – it is dangerous!!!!. It’s most likely in the rack, but, it’s possible that someone has hit something and broken the rack loose from the anchor bolts/ locating loops. If this is the case the whole rack could slide left or right in answer to oposing force from the steering. Either way it could be really exciting. Whatever the problem is DO NOT DRIVE THE CAR untill it’s fixed.
