1996 XJS I6 bogging under acceleration
#1
12-21-2010, 01:47 AM
1996 XJS I6 bogging under acceleration
Let's get the annoying stuff out of the way:
I've been through a lot with the engine. It's got new O2 sensors, a new MAFS, new fluids, a new air filter and a freshly cleaned intake system. It recently passed both a smoke and a propane test just fine.
Everything was wonderful for a few days. Then, it decided to spend a couple of days misbehaving from cold starts. Occasionally, the power brakes would be gone for a few minutes. It stumbled at stop lights a few times, and it died once. It's been taking a little more time to start than before.
Then, I drove it from NC to PA. I ran a can of Seafoam through the tank to help clear anything that might dislodge after the cleaning. It worked out fine, and the drive was entirely uneventful. Everything was cool.
When I arrived, I got a few days of trouble free motoring, and then things went wrong again. Whenever the throttle is applied to any degree beyond granny speeds, it just bogs and stutters until you back off.
It is drivable, and it's going to carry me back, but it's going to be annoying.
There are no codes being thrown. Everything on the vehicle has been sorted over the past few weeks, and it was running fine. The cold weather might have something to do with it, but it may be a coincidence.
If anybody is out there, I'd like some suggestions today. If you read this thread and have even the slightest idea that may be helpful, go ahead and reply. It won't hurt to have other opinions.
I won't have much time to work on it tomorrow. It's cold as heck, I have limited tools, and I have no garage up here, being restricted to one space in a persnickety town-home complex. This is what happens when you visit relatives.
My other thread, updated recently, details the work that has been done so far.
I've been through a lot with the engine. It's got new O2 sensors, a new MAFS, new fluids, a new air filter and a freshly cleaned intake system. It recently passed both a smoke and a propane test just fine.
Everything was wonderful for a few days. Then, it decided to spend a couple of days misbehaving from cold starts. Occasionally, the power brakes would be gone for a few minutes. It stumbled at stop lights a few times, and it died once. It's been taking a little more time to start than before.
Then, I drove it from NC to PA. I ran a can of Seafoam through the tank to help clear anything that might dislodge after the cleaning. It worked out fine, and the drive was entirely uneventful. Everything was cool.
When I arrived, I got a few days of trouble free motoring, and then things went wrong again. Whenever the throttle is applied to any degree beyond granny speeds, it just bogs and stutters until you back off.
It is drivable, and it's going to carry me back, but it's going to be annoying.
There are no codes being thrown. Everything on the vehicle has been sorted over the past few weeks, and it was running fine. The cold weather might have something to do with it, but it may be a coincidence.
If anybody is out there, I'd like some suggestions today. If you read this thread and have even the slightest idea that may be helpful, go ahead and reply. It won't hurt to have other opinions.
I won't have much time to work on it tomorrow. It's cold as heck, I have limited tools, and I have no garage up here, being restricted to one space in a persnickety town-home complex. This is what happens when you visit relatives.
My other thread, updated recently, details the work that has been done so far.
#2
12-21-2010, 02:21 AM
I had EXACTLY the problem you describe with the AJ16 in my X300. It's a long shot, but quick and easy to check: make sure there are no foreign objects between your air filter and MAF.
More info:
There were no check engine lights, and the first thing I did was check and clean the spark plugs and coils. This didn't make any difference.
So I went on to check the air filter - it wasn't too dirty, so I continued down the line and took out the air flow meter. it looked OK, but when I removed it, there was some debri between it's intake mesh and the air filter - wasp carcasses etc. and I heard a leaf* fall out and scuttle down through the engine bay. At the time I thought nothing of it - some muppet had obviously been careless when replacing the air filter, and let crap fall into the line.
I decided to swap in the air flow meter from my dads X300, and what do you know, the car runs perfectly. Oh hell, thinks I, seeing the 700 quid price tag on a new air flow meter.
Anyway, I couldn't help but try my air flow meter in my dads car just to be 100% sure it was fault, but the damn thing worked fine. No I was confused.
*Then I remembered the leaf. I hadn't even seen the thing, so I guessed what size it would have been, and made a replica leaf out of masking tape. Sticking it to the intake mesh of the air flow meter, I fired up the car, which promptly chocked to death. I moved the masking tape leaf down to a lower position on the mesh, and the car idled, but would not rev properly: just like the original fault. In some positions, the masking tape seemed not to affect the car at all.
More repositioning of the masking tape confirmed it: The phantom leaf had been the culprit. It hadnt been blocking the air flow to the engine, but rather changing the aerodynamics of the tube feeding into the air flow meter. This was confusing the air flow meter, and making is send false information to the computer, which stopped the car from running properly.
Moral of the story: Be careful when you service your air filter, and ensure that no engine bay rubbish falls down behind it!
#3
12-21-2010, 02:16 PM
Veteran Member
#4
12-21-2010, 03:53 PM
Veteran Member
Sounds to me like fuel starvation, there's enough at low speeds and low power demand, not enough when you want power for acceleration and higher demand. However, I suppose it could be ignition, but lets keep to one thing at a time !
Two possible things as fuelling cause, (as I see it) -
1. Fuel pressure at the injectors is insufficient, so although pulse length is OK not enough fuel passes through.
2. ECU is not commanding enough supply based on false sensor readings, so pulse length is too short. You wont get any fault codes if the ECU thinks things are OK. Sophisticated systems cross-check sensor readings and flash up warnings if things seem out of range, but I don't know how sophisticated the system is on a 1996, maybe Doug does.
For ignition, there is the possibility of the crank position sensor starting to fail at higher revs, but I am only guessing here, as this is outside my personal experience.
What would make the pulse too short ? Well, the biggest influence on engine fueling is engine temperature and mass air flow, so MAF box needs checking, and also the engine temperature transmitter to the ECU. Sometimes these are things like corrosion at electric line connector plugs, so unplug and clean these as you have no real workshop facilities.
Two possible things as fuelling cause, (as I see it) -
1. Fuel pressure at the injectors is insufficient, so although pulse length is OK not enough fuel passes through.
2. ECU is not commanding enough supply based on false sensor readings, so pulse length is too short. You wont get any fault codes if the ECU thinks things are OK. Sophisticated systems cross-check sensor readings and flash up warnings if things seem out of range, but I don't know how sophisticated the system is on a 1996, maybe Doug does.
For ignition, there is the possibility of the crank position sensor starting to fail at higher revs, but I am only guessing here, as this is outside my personal experience.
What would make the pulse too short ? Well, the biggest influence on engine fueling is engine temperature and mass air flow, so MAF box needs checking, and also the engine temperature transmitter to the ECU. Sometimes these are things like corrosion at electric line connector plugs, so unplug and clean these as you have no real workshop facilities.
#5
12-22-2010, 01:02 PM
Hi Kennith,
I had EXACTLY the problem you describe with the AJ16 in my X300. It's a long shot, but quick and easy to check: make sure there are no foreign objects between your air filter and MAF.
More info:
I had EXACTLY the problem you describe with the AJ16 in my X300. It's a long shot, but quick and easy to check: make sure there are no foreign objects between your air filter and MAF.
More info:
I'll be checking thoroughly. I've got a few hours before the drive.
#6
12-22-2010, 01:07 PM
1. people will have you consider a fuel filter
2. I think you might want to clean out or replace your EGR Valve. I had similar issues, but my engine would stall out. Turns out it was either the filthy throttle body, or the EGR valve. Both were absolutely filthy.
I own a 1996 XJS as well.
2. I think you might want to clean out or replace your EGR Valve. I had similar issues, but my engine would stall out. Turns out it was either the filthy throttle body, or the EGR valve. Both were absolutely filthy.
I own a 1996 XJS as well.
2: It's on the list to do when I get back. I'll be replacing that and whatever is involved with the brake accumulator as a matter of course during this investigation.
Last edited by kennith13; 12-22-2010 at 01:09 PM.
#7
01-13-2011, 01:21 PM
Senior Member
My 1994 XJS was doing similar things and I checked all the things you did with not much improvement. Until I removed the engine ECU and checked the connections.
The convertible has the ECU in the Passenger (RH seat) in the front door frame kick plate. Sit in the seat and look at where your right foot is. The ECU is behind the plastic cover in the footwell/doorpost.
I removed the connectors, aha ! Green crud was encrusted on the pins on 1 edge
of the connectors. I cleaned the connections with a can of Contact cleaner from Radio Shack. Most auto parts stores have something like it.
Be careful with the spray.
It will cause some hard plastics to disolve. I accidently sprayed the window switch bezel and it just crumbled !
Well, after the ECU was put back in and the battery hooked back up, the XJS purrs!
It doesn't stall or hesitate on acceleration now.
I was getting intermittent Check Engine just prior to my checking the ECU.
The convertible has the ECU in the Passenger (RH seat) in the front door frame kick plate. Sit in the seat and look at where your right foot is. The ECU is behind the plastic cover in the footwell/doorpost.
I removed the connectors, aha ! Green crud was encrusted on the pins on 1 edge
of the connectors. I cleaned the connections with a can of Contact cleaner from Radio Shack. Most auto parts stores have something like it.
Be careful with the spray.
It will cause some hard plastics to disolve. I accidently sprayed the window switch bezel and it just crumbled !
Well, after the ECU was put back in and the battery hooked back up, the XJS purrs!
It doesn't stall or hesitate on acceleration now.
I was getting intermittent Check Engine just prior to my checking the ECU.
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