Hi folks. I had previously posted about 6 months ago or so about a stumbling problem under load on my 2004 xk8. I had posted that the dealership diagnosed it as a bad MAF, which they tried to explain that it was sending incorrect data to the ECU resulting in a fuel pressure issue. The drive home that day was not far and due to traffic I didn't have a chance to really test it. I then was away on business so a few weeks later I ran the car and had the same issue, and then with every few additional miles it seemed to be getting worse, nearly undrivable with anything over 1/3rd throttle. So I brought it back and they gave me credit for the MAF and diagnosed a bad fuel pump, as the pressure would drop from 55lbs at light throttle to 5 to 10 under full throttle. After a week in the shop getting the fuel pump replaced and $1200 later, the car ran GREAT! A week later I consistently had a hard start problem after the car sat for 30 mins or more, but once started ran fine. The Dealer diagnosed a bad check valve on the new fuel pump and installed another at no charge of course. Problem was fixed, then about 2 weeks later, same hard start issue again. Dealer said that pump was bad as well so they replaced it again, which fixed the issue. A few weeks later, same problem again! This time they requested a fuel pump from a different Jaguar warehouse with a different lot number thinking they had a batch of new defective pumps. This pump lasted about 2 months or so but ust started acting up again with the same issue, fuel pressure loss when sitting for 20 or so mins. Can all of these fuel pumps really have bad check vavles? Clearly each time they replace the pump it fixes the problem, so it seems that they really are bad. But I wonder if there is some kind of fuel line connection issue somewhere that gets "fixed" temporarily when the mechanic is wrangling things around replacing the pump, and then over time, it works lose again until the next time the mechanic is moving things around again to replace the pump again. Has anyone experienced a rash of bad pumps like this? Any other thoughts?

 

Steve
Did they ever replace the fuel filter? Some members have had problems with dirty fuel filters. Possibly these pumps are working overtime to get through the sludge. When my cars pumps went out The first thing I did was opened the fuel line up at the filter check for fuel pressure. Then installed a new filter. haven't read of a rash of bad pumps.

 

Not to say that a number of fuel pumps could or could not be defective, I am more inclined to think the problem (still undetected) is beyond the fuel pump - maybe an electrical or mechanical gremlin.
Rev Sam had a post some time ago that described a loss of pressure and slow start problem like your's. After installing a check valve in the fuel line which appeared to fix the problem, he eventually replaced the fuel pump and discovered a check valve tab broken, permitting fuel to spray inside the tank rather than hold pressure in the line, thus creating a hard start and loss of fuel pressure. The replaced fuel pump solved his problem.

 

Thanks for the replies...yes, the filter was replaced at the first pump change out. Each and every time it goes into the shop they connect a mechanical gauge at the rail/shraeder valve and without question pressure is dropping, so it is not an electrical issue. As far as Sam's issue, yes it was the check valve which is part of the pump assembly on the 2003 through 2006 cars. The dealer thinks these check vavles are all defective on the new pumps they are installing. I am wondering if a connection somewhere near the pump/tank is funky and when they pull the tank the movement could temporarily "seal" up but after a few weeks starts leaking? I doubt this since I smell no fuel ever, and I would think I would since the car is in the garage unless I am driving it, but just wondering/thinking out loud.

 

I'm not that familiar with the AJ-V8---Could the fuel pressure regulator at the rail be the problem? I know on other cars if this fails the diaphram in the regulator is the culprit allowing fuel to release into the vacuum line. Just a thought.

 

Steve,
Have you successfully resolved your multiple failed pump problem?

Looks like I'm headed for a similar experience. I took your advice and had the pump professionally replaced. Good thing too, because 400 miles later the slow start problem is back.

I'll have to wait until Tuesday to call them but did you end up with any diagnosis beyond "bad pump"? Was there a "good" source?

Thanks.

 

I too just had a new pump installed. It was not a dealer. The whole job along with a new filter was $575. I was very happy since my son just put several new pumps in his Ford pickup, and the pump alone was over $500. His failure was the gas gauge would not read correctly but it took three new pumps before they got it fixed. I'm thinking you have a ground problem. I have found several ground studs on Jags that have paint under them. I can't tell you where the pump grounds, but if you could find it, and take it loose and sand the paint off, the problem may be solved.

 

Steve, this may be one of those issues where the UK and US are divided by a common language but can you tell me what you mean by a "hard start" problem? Did it take a while to fire? Also, really interested to know if it was any different if the car was left for a few days or if it still was difficult to start.

 

Theretwo other parts in the system that may be bad, the pressure sensor and fuel pump module. This system is a non-return type with a pressure sensor that regulates fuel pump voltage to maintain constant pressure. The sensor may be sporadic. There is also a module that the senor runs through, it too could be bad.

 

It is hard to know if it truly is fixed this time. Yes, I have the car back from the dealer and it has been 2 weeks since the pump was replaced again, and it still is working fine, but that previous pump lasted about 10 weeks (the longest out of any of the replacements), so I really don't know if this one will be ok or not, only time will tell.

To note: When I picked up the car this last time I had a lengthy coversation with the service advisor and the technician. I have no doubt the tech knows what he is doing and he has 20 plus years experience working on Jarguar cars. He is as perplexed as anyone about this. He setup the old pump with a short deadheaded fuel line with just a mechanical pressure sensor and confirmed it was not holding pressure. He showed me the setup. This without question eliminates everything else in the car. Also, I may have mentioned this in a previous post, but he told me that my fuel tank is pristine clean inside. I had suspected maybe some foreign particle could be picked up and then gets stuck in the valve keeping it from sealing well. I am not saying that couldn't still happen, but with a very clean tank it is less likely, and I really beleive it would be much more prevalent with others if it truly were that sensitive. And again, I may have mentioned this, but the pump that was removed looked like new when the tech showed it to me. I looked closely at the check valve area where Rev. Sam mentioned the plastic tabs that hold the fuel line had been broken and this connection was perfectly solid.

 

a hard start in this situation: Long cranking times before the engine starts. Normally, when turning the key to start the engine, it fires up almost immediatly. When these pumps have failed, it can take about 20 to 30 seconds of cranking before the engine starts, and when it does finally fire, it stuggles at first as fuel pressure builds, so it will catch slowly at first. If I were to let off the key as normal, it would not stay running, I have to keep the starter engaged until it truly is running. I don't drive this car every day as I work out of the house. Generally I drive it a couple of times a week, and quite a lot on weekends, but during the week it could site for several days. With a good fuel pump, the car can sit for weeks without a hard start issue, it will fire up immediately. When the pump/check valve goes bad, there is no warning signs, it is as simple as I go to start the car and it will take 20-30 seconds of cranking time to catch. Once running, runs fine, normal 55-56 lbs of pressure. If I shut it off then restart within about 2 minutes, it starts fine. If I let it sit for longer, say 5 minutes, it will take a bit longer. If I let it sit 10 minutes or 10 hours or 10 days, it makes no difference, it will take 20-30 seconds of cranking to start. Also to note, this hard starting thing is not intermittent. Once I have that first hard start problem, it always had it as described here, it is not a situation where every once in a while I experience it, it is alway like this until the pump is replaced again.

Lastly, someone else mentioned possibly the fuel pressure sensor or the fuel pump control module. My tech would like nothing more than it to be either of these. He veryified with a mecahnical gauge at the fuel rail that the fuel pressure is dropping to zero when the car sits off, then installed a new pressure sensor and still had the same pressure drop. Installed a new pump, verified no pressure drop. I really don't think it can get more definitive than that. That is not to say other people's cars may not have different root causes.

 

In your conversation did the tech happen to note where it was leaking from?

I took the scenic route to find the problem in mine but with the pump sitting on the bench all that need be done is fill the putput line with fluid and I could watch it drip, drip, drip, out the bottom of that little silver pressure regulator as the tube emptied.

If the pump were submerged you would never see this though.

 

Interesting that it is the pressure regulator on yours. He did not mention to me if he knew where exactly it was leaking. When we looked at the pump together he did point out the regualator, but only as a simple matter of reference. We both looked closely at the check valve area, and I think if he realized or knew it was the regulator he would have mentioned it. I wonder on yours if under pressure with the correct flow direction you would have seen the same leak. I would really have to think it would, but, at the same time I would think that you would have expereinced drivability issues, particularly under load, if it was leaking like that with litterally no pressure. I wish that I could have kept the puump, but being that the part was still under warranty, that was not an option.

I am not sure how clear this was made in my scenario, but the very first problem I had with the original fuel pump was not a check valve issue, but low pressure under load. The engine would stumble and slow down under 3/4 throttle, and my OBDII fuel pressure readings showed 55 lbs at idle, but only around 10 lbs of fuel pressure under heavy load. And even though the ECU monitors fuel pressure, there never was a code, no misfire code, no low fuel pressure code, no lean, no nothing.

 

My guess is that there would be a pretty good spray if the pump was running but it really was not a big leak. More of a drip. It took perhaps 10 sec or so just to drain the 8" of tubing attached to the pump.

It's possible that it was not so bad as to be something the pump couldn't keep up with when running but was enough that when the pump was off the pressure could bleed down.

I'm going to drop the car off on Wed to get the new (same symptom) problem diagnosed, so we'll see what happens from there.

Thanks for the advice to get it professionally done, by the way. If it does turn out to be the pump, then a professional is definitely going to have an easier time with a warranty claim than I would by myself.

 

Finally I see others with the issue I've been fighting for a year and a half. I've replaced two fuel pumps, checked wiring, replaced the fuel control module, pressure valves were going to be next. I was even looking at replacing the battery as someone indicated really weird things happen as a battery ages.

My symptoms were very similar but once things failed, I could never get the car to restart. I even had my self convinced it worked fine with the top down, but not up, that led to checking for pinched or rubbed wiring. It was driving me crazy. I even had a couple of instances where just putting the cat on the flatbed for the tow home would reset things and the car would start and run for a few days just fine.

One other thing I did notice was the exhaust smell, normally I never even notice it but just before the fuel delivery fails the exhaust smell would get very sour, over a couple of days.

Now it's going into the shop and let them figure it out, at least if the fuel pump fails after they install it, it should be replaced on them.

Hope one of us can truly find a resolution.

thanks
mjw

 

Well folks, guess what...it looks like once again another bad fuel pump check valve. I think this is fuel pump number 6 that is in the car now, number 6 since march of this year (2012). I put about 300 miles on the car since the last pump was installed about 4 weeks ago, and this morning had the long cranking times again. I am I wondering if anyone has an opinion on installing a separate inline check valve such as this Interestingly, a review on amazon on this part was from an xk8 owner. Any opinions? Quite honestly I don't think I can keep this car if I continue to have this issue without a real solution.

 

Wow.... Someone needs to question the fuel pump supplier's quality-control program if you've been through six fuel pumps in only six months. Unless your car is experiencing electrical surges that could be damaging the fuel pumps after just a few hours of driving....

 

Steve
Are you using ethanol? There has been some discussions about fuel pumps that are made that will not hold up to the 10% ethanol blend, This may be one avenue you can look into. I use a 10% ethanol blend but my pumps are Bosch and I don't have any problems.

 

Our fuel here can be up to 10% ethanol, but I have no way to know exactly what percentage we actually have at the pump.

 

An in line check valve would work but you need some kind of pressure relief mechanism. The pump assembly has a small regulator after the check valve to limit the maximum pressure.

If you don't have something to relieve the pressure then when you shut it off the heat in the engine bay will cause the fuel to expand increasing the pressure.

In that situation you can get hard starting because the pressure is too high. I think the Rev commented on that in his thread from long ago when he tried the in line check valve.

One other thing you might check is the manifold connection to the fuel pressure sensor. This gives a manifold pressure reference for the sensor to control to. Yesterday while doing something under the hood I found that mine had popped off for some reason or other.

On the XKR the sensor is on the right hand side at the front of the fuel rail. I assume the XK8 is located somewhere near there.