V8 Reluctant to start

As you all probably know the car usually starts at the turn of the key but of late it occasionally won't. Starter turns and everything but engine won't fire unless you pump the accelerator. So is it a fuel line problem? ECU? MAF? What are your thoughts / checklist if I want to systematically eliminate possibilities?

Cheers!

Could be MAF Sensor............... You tried Cleaning it ???

My 4.6 is doing the same. I read here about the stepper motor for the idle control. Took it out and it was filthy. The seating was caked with carbon. Cleaned it all out and so far it has started on he button (Not been out in it yet as I need to find out why it keeps flattening the battery!)

Just an update, the car's at the garage. They are suspecting crank position sensor. Since I happen to know these guys are slightly prone to throwing new parts at a problem and hoping it will go away, I'm going down there this afternoon to check wires and connectors first and will also make sure MAF and stepper etc are cleaned.. thanks for those tips!

rasheed said:

Just an update, the car's at the garage. They are suspecting crank position sensor. Since I happen to know these guys are slightly prone to throwing new parts at a problem and hoping it will go away, I'm going down there this afternoon to check wires and connectors first and will also make sure MAF and stepper etc are cleaned.. thanks for those tips!

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IF it WAS the CPS it wouldn't start at all no matter how much yer pump the Acc CPS would kill the Spark NOT the fuel ...

Hang on though............... I suppose if its dirty & not gettin a "Clean Sense" it COULD be the problem... Jags are prone to CPS problems my Son-in-law has chenged 3 on his XJ series!!!!!

Well I spent the afternoon there and and we first did the usual servicing of changing engine oil and replacing oil, fuel and air filters. Also cleaned the MAF and the throttle body and checked all cables and connectors. Put it on T4 and found the following stored faults, ECU-BECM link sync failure and Cam and Crank position sensor mismatch. Cleared them and reset the GEMS ECU to default (because of the cleaned MAF). So far have done 20 starts without a problem and car seems to drive very smoothly indeed. Partly due to the new oil and filters no doubt but just wondering if the ECU default settings actually are best? Is there a way to keep the ECU from gradually "adapting them to driving conditions" because really its very very nice right now!

So far so good, then. Will report back if the starting problem re-appears. I can't honestly say which of the steps taken appears to have cured it. Will be going back in a week to read fault codes again and see if the position sensor issues have re-appeared.

aaaand its back. will go in again tomorrow maybe (if they've a slot) and have codes read.

You can't stop an adaptive system adapting.

What you really need is fully working sensors, then you wouldn't have any problems.

Don't use non genuine air flow sensors either. Buy one marked SAGEM at a breakers. Most aftermarket MAFs will end up messing the adaptives up and you'll have to have the GEMS adaptive settings reset to sort it out again. Then again, the codes that T4 have presented are not MAF related. Normally they would give rich or lean fuelling codes and HO2 failt codes.

It looks more like you need a new crank sensor (or you've got a damaged reluctor ring on the flywheel) and/or a cam sensor. You can get both scoped to check the waveforms are OK. These sensors are not that cheap, especially the Cam sensor.

You've also got an issue relating to comms between engine ECU and the Body Control ECU. I wonder if you could have a failing engine ECU?

Cheers WSLR, your post was exactly what I was after. A sensible list of things to do. Quick question, what do you mean get the sensors scoped? I assume you mean to test feed various signals and watch the output on an oscilloscope but out here you see I'd have to do it myself. So where might I get detailled procedures as I'd need to know what voltages to feed and what readings to watch for?

ps. can anyone give me part nos for these two sensors? is the crankshaft speed sensor the same as the crankshaft position sensor?