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I posted once before about needing the firing order for this car and I got the answer, THANK YOU again to the person that answered me. We have another question, my dads been having a hard time with this car and even took it to a Jag specialist but they couldn’t figure it out either. The issue is, it backfires in the throttle body. He’s changed the plugs and the timing chain is good. What could possibly be the issue?
Need help with figuring out why it backfires in the throttle body. Plugs have been changed, timing chain is good. We’re stumped.
Last edited by GGG; Aug 14, 2019 at 02:50 AM.
Reason: Post was locked for moderation - text coding repaired
Surprising that a specialist couldn't figure it out! Thats disappointing.
Backfire is often related to ignition timing or a lack of it. A major conponent failure like ignition modules or crank sensors would set codes in the ECU. Did the shop come up with anything?
Lets get that Rose Bronze beauty back on the road. Its a rare color on an already rare car.
Thank you SleekJag12.. And nope, they came up with nothing. They had the vehicle for almost 2 months too. They called my dad to come get it, so when he gets there, no car. They accidentally gave it to someone else!!!! He of course got it back though but sheesh! Yesss, we need Rosie back on the road!!
May be an obvious question but how did this condition start. was the car running ok until what point? It almost sounds as though the firing order might be out of sequence, worth checking that again?
Hello. My very first question in this forum was the firing order. Another person provided that, that wasn’t the issue. Wish it was.
Double check from the diagram above.
My main question though was how did this start? These problems are usually the result of something that happened... in my case I fix something and mess something else up. Was the car running ok previously and what was your dad doing to the car before the problem started happening...
He said the car was running perfectly. He changed the power steering pump. He started the car and it was running but it was making noise like something was hitting the fan. He turned it off to check it out and everything looked fine, he restarted it and it wouldn’t run again. That was the last time it ran.
There are 2 crankshaft position sensors ,on the V12 one in the front and one in the back
Sometimes the face of the sensor gets dirty other then the connector , the ECU will get lost if not a good signal as it has a designed in hunting or learning which crankshaft rotation is the true # 1 TDC
if you put your finger on the # 1 fuel pump relay do you feel it click 3 times
The first 2 clicks is for 4 seconds to charge the fuel lines , this line pressure should hold for days
The 3rd click is by the crankshaft position sensor through the ECU and will keep the fuel pump running for the duration of your drive by design
In your start sequence the trapped fuel charge may have bleed off and requires a couple of ignition key rotations to charge the fuel lines
The missfire may be a sign the CKPS was failing
To bypass the fuel pump enable and Keep # 1 on jumper relay socket # 30 to # 87 or just put power on # 87 ( fwd socket )
Don't just jam a wire into the sockets as the pumps are current dependent and won't run properly so use blade connectors
Are all your engine ground wire terminal post cleaned ? Around 5 of them including the main large engine block ground strap at the starter which causes weird problems
I the heat of battle the ECU on the inline 6 engine needs 11.4 volts or no proper ECU operation ( spark control )
Watch your volt gauge for sag below this point ( the V12 ECU is probably in the 11,4 volt area )
Last edited by Lady Penelope; Aug 17, 2019 at 08:25 PM.
Wondering what the 'something hitting the fan' noise could be after fitting the new power steering pump. Is the fan ok? did anything actually hit it or was it a similar noise? If the car was running fine before there has to be a clue here. Was anything else damaged or knocked out of place when installing pump?
As far as he knows, yes the fan is ok. If anyone is open to talking to him or myself on the phone, that would be awesome and would probably give a better understanding. He’s not very good at messaging that’s why I’m doing it for him. But I feel like I’m totally clueless as the middle man. You can message me @ 1-719-321-3811
I've only had my XJ12 for 10 days so still familiarizing myself with it, I am more familiar with 60's and 70's Jags, so I'm probably not the best person to discuss around specifics unlike the super resource 'Lady Penelope'.
My logic with all problem solving is 'what changed'? If the car was running fine, then the ps pump was removed and a new one fitted, then there was a noise like something hitting the fan, what was dislodged or damaged around the ps pump area that might have caused that? What could cause that noise and why would a misfire then start?
There are a lot of sensitive engine management components on these engines, did you knock anything out of position? did you try running an obdII reader on it to see what codes it threw? (I am using a cheapo $15 amazon one, see my other post).
I'll look on my 96 car around the ps pump for clues later today...
Are the 3 sensors the same part # and are swapable for troubleshooting being the Cam sensor is only used in the starting sequence ? It may take more engine rotations with the Cam sensor INOP . To test this remove the connector to get that information before swapping sensors
Based on that new info, your most likely suspect is the front crank sensor. It resides immediately behind the lower crank pulley at the bottom of the crankcase as shown in the diagram. The belts probably had to be removed for that p/s pump job, and the alternator belt runs very close to the sensor.
Check the sensor for damage and make sure its not loose. It should be clean. Also check the leads as they are in a tight spot too. A broken wire could easily contact the fan or pulleys.
Keep the info moving... we can probably get that car moving soon too.
The easiest thing to do and yourself is to clean the face of your sensors and grounds and jumper the # 1 fuel pump relay
The alternator belt if too loose can cause problems in other areas that we will get into later and if you alert me with a Private mail to alert me if you are in a Private Mail bind and timely attention
Last edited by Lady Penelope; Aug 19, 2019 at 08:57 AM.
in a non conventional manor you can remove the power steering pump and the adapter section
You would have to make a wooden plug for the hole in the engine block
Did you or the mechanic set aside and save the replaced coils as cheap brand new coils can cause problems in running as they can indirectly effect the ECU power that operates the ECU as a whole and not a sub-system like your ignition
By parts being replaced you my have a changing set problems and the challenge is to differentiate the original issues and new , this is common in a imperfect world
The first way to look at it is a running problem then a starting problem as this seems to have changed
1995 Jaguar XJ12
