Missfire and popping

I am at my wits end. We recently bought a 1998 4.0 v8 and have had all manner of problems. After a head re-build, brain un-lock new plugs and leads (the firing of which has been proven) I am left with a misfire and loud popping of air when pressing the accelerator. This results in a severe lack of power and the rangie stalling.
Could this be an air fuel mixture problem? If so does anyone have any idea how I can resolve this?

Really don't want to give up just yet.

A head rebuild? just one? if job done correctly should have no problems. You could have an air leak. Be very carefull and with a fire extinguisher to hand spray some engine start around the air intake area, whilst the engine is idling, and anywhere that could leak air. If the revs suddenly change then you have found the leak.
Ideally you need a local independant to do a diagnostic. And whilst waiting do a compression test to prove the work done.

Other areas to look at are fuel pressure, Lambdas, Maff etc etc etc but start with the basics

Hi. The problem was there before re build.
How is best to check for air leak.

ibateman said:

Hi. The problem was there before re build.
How is best to check for air leak.

Click to expand...

Read my post again !!!

Could be a dodgy MAF

Run the car then unplug the MAF, if the engine changes it is a dodgy MAF....if it still runs rough then MAF is most likely OK!

Sorry to be a bit dim but what is the maf?

Mass Air Flow meter, it measures the incoming air and telss the ecu so it can use the right fuel map.

If it is duff when you unplug it there will be no change to engine running, if it works ok, when you unplug it the engine will run rougher.

Thanks for that. That is job number one tomorrow morning.

i had the same problem last week i fitted a new maf sensor and now runs better than ever

ibateman said:

I am at my wits end. We recently bought a 1998 4.0 v8 and have had all manner of problems. After a head re-build, brain un-lock new plugs and leads (the firing of which has been proven) I am left with a misfire and loud popping of air when pressing the accelerator. This results in a severe lack of power and the rangie stalling.
Could this be an air fuel mixture problem? If so does anyone have any idea how I can resolve this?

Really don't want to give up just yet.

Click to expand...

Does sound like the classic symptoms of the mixture going weak due to lack (or incorrect) signal from the MAF - before condemning it - make sure it is plugged in properly - the connector has to be pushed in all the way. Also you could try removing it and cleaning it with electrical contact spray - let the resistor dry and then refit.

The car should actually improve once running and then the maf disconnected.

The ecu sees the maf as totally failed and runs on back up fuel trims.

Unfortunately it will not start with the maf disconnected.

Thanks for your responses.
This morning I manually restricted the air intake and the rangie showed signs of improving so new maf now ordered.
Thanks again.

So, this morning, new maf in hand I confidently fitted and started the rangie.
But..... Bad news. Popping and lack of will to do anything still present. Checked for air leaks and everything seems good.
Any ideas anyone?

Could it be the timing???

I am not too good with engines. How could I check this or how could it have been knocked out in the first place?
Thanks for your reply.

Send the MAF back and get a refund. I would put money on an air leak. The best way to find this is as mentioned a spray of carb cleaner or similar or better still a smoke test. A look at some live data and the long term trim values will give you a good clue to whats going on. If your not happy with doing this yourself then take her to a good indepent for a session, it will be money well spent. Dont just through cash at it on second guesses.

Well. I have today gone over the whole air intake system and can find no leaks. The car will rev up lovely on the drive but as soon as I try to drive it starts with the popping and lack of power. Any more ideas?

Could this be the crank shaft position sensor?

had the same with my 4.6 v8 tried new filters maf sensor etc but problem still there took to garage and no faults were showing so i left it with them to hopefully sort out. Turned out it needed new coil pack.

Look at the wires/HT leads when dark, any visible sparks and they are fubar - just an easy free thing to check

When were they last changed? (First thing i had to change on mine and what an improvement)