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Update: This was originally posted on the Jaglovers site and i wanted to share it with these members as well
I wanted to update the board on my progress or lack thereof on my fuel pump issues. Just to recap I have two 94 XJ40s. Both have the exact same fuel pump issue (fuel pump not running). I have a black one and a green one. The green one I just purchased as a parts car. The PO sad it developed a crank but no start and after a year of trying to start it he gave up. Upon receipt of the car it was in such good condition I decided not to part it out but to try and get it to start.
Now the black car I wasn't driving and after letting it sit for a few years it had water and trash in the tank and it would not stay running. So I decided to pull the tank and clean it and also cleaned the entire fuel system. i also replaced the pump. Once I put it back together it would crank but not start. It was doing the exact same thing as the green car.
On both cars the fuel pump would not run unless you applied 12 volts straight to the fuel pump protection module (FPM). I have discovered that in the 94 Jags, and it could be in others, that Jaguar placed an extra fuel pump plug in the trunk that stays hot all the time that you can plug the FPM into and immediately test the pump to make sure it works.
On both cars once the FPM was plugged into the 12 volt always hot plug the fuel pump would run but it still would not crank. So I knew the FPM was good and that the pump was running but it still was not getting gas to the fuel rail. I checked and rechecked all the fuses and I found two fuses bad on the green car that caused the transmission relay socket and the fuel injection ignition on relay sockets not to work. the PO of the green car did not know that the fuses were blown or that the relay plugs were not working.
On the Black car all the relay sockets were hot but I wasn't sure whether or not the relays were good so I purchased a cheap relay tester to test all the relays I could find on the car.
I found four bad relays in the black car and three bad relays in the green car. Once I replaced all the bad relays in the Black car it started right up. I have not tried to start the green car but I know it will start as it had the exact same problem. I also cleaned and checked all the grounds in the car.
Moral of this story for no crank/start issues is to buy a good quality relay tester and test all the relays you can find in the car. These relays looked smack brand new and they were bad. Also I had a limp home mode fault that went away as soon as I replaced all the bad relays. I replaced the relays with Bosch relays as there were just too many Hella relays that were bad.
Hi Motorcar man:
It was just not the blue Hella relays it was also the Black ones. I plan to go thru the hole car and replace them all with Bosch relays just as preventative maintenance.
This thread was quite timely, and I wanted to jump in and add my own experience.
I was not aware of the problem with these relays, and had been having a similar "intermittent start" problem that I'd more or less just been living with. (I decided that the ~50% successful start ratio was something I could live with on a car I didn't drive everyday) The car would always run if I just hit the key a second time.
After reading through the TSB so kindly posted above, I picked up the same relay tester linked here and a pack of cheapskate "waterproof" relays with appealing specs, linked here:
My first observation is that the relay tester, although inexpensive, is really quite good. It is "intelligent" to some degree, and the test consists of cycling the relay 10 times and monitoring the outputs, illuminating an LED either green or red after the test. All but one of the "blue" relays failed the first test, although subsequent tests usually passed. I suspect that 20 cycles in two minutes is more than enough "exercise" to get them to work reliably in the short term.
On to the relays: I'll admit to feeling a bit guilty not buying Bosch, or the new "improved" relays recommended by Jaguar for this, but the set linked above were billed as waterproof, had specs that exceeded OEM, and had a really slick diagnostic LED built in. At $14 for all five, it was an easy sale. If these were harder to get to, I likely would have handled things differently. My first observation is that these aren't /quite/ waterproof. Note what appears to be a vent hole between pins 30 and 85. In the listing photo, that's plugged with epoxy. On all five of the ones I ordered, it is not. It should be a quick fix with some silicone, epoxy, lip balm, anything. I have not yet done this, but I really should. Maybe even "will."
A couple before and after photos of the relays - You'll notice two of the "improved" black relays that were clearly installed by the previous owner. Re-reading g7162002's post, I now realize that I should pull and test those, too.
This photo taken with the engine running, and the status LEDs strutting their stuff. If I'm not mistaken, the one on the right is the AC compressor, which was inactive when this was taken. Everything looks good!
And lastly, the fuel pump relay in the trunk:
So far, it appears swapping this relay may well have fixed my start issue. I was thinking it would be a crank/cam sensor, but the blue relay that was installed here definitely failed the test, and the three times I've started the engine since installing this new one, it's fired right up and purred like a... Jaguar.
Many thanks to the veterans of this forum. Your collective experience is greatly appreciated. The TSB above, g7162002's experience with the tester, and the PDF of this car's electrical system I've found elsewhere, were invaluable. If there are more of these relays installed elsewhere that I didn't find, please do let me know.
One issue to be aware of is that not all of the relays in your car are the same. Some have a resistor and a clamping or de-spiking diode across the coil to prevent voltage spikes from damaging the transistor control circuits in your ECM and other modules. When a relay coil is de-energized and the magnetic field collapses, a voltage spike of 200+ volts can flow upstream into your electronic modules. The resistor and diode are there to ensure that any spikes are shunted downstream to ground instead. Here's a snip from the Engine Management schematic showing three of the relays that have resistors & diodes:
I think I recall that the relays with resistors are the violet ones, but they may be brown. Bob will probably remember.
If you can't find relays with resistors & diodes, you can add a resistor of 600 ohms or more and a standard diode (I think I used 1N4002 diodes but I could be wrong).
Im just happy that I can help someone else. I purchased my first Jaguar in 2006. While I was a pretty decent mechanic for working on my own cars. I knew absolutely nothing about working on classic jaguars. But with the help of these forums I can now say Im a pretty good Jaguar mechanic. One thing Mike that I need to mention about the relays you purchased is that , yes they are cool looking.
But I see it says 60A. My father was electrician and he always preached never to put a bigger circuit breaker in other than what's required because you could burn a house down in that the breaker/relay would not trip and cut the power if need be. Therefore, possibly burning something up. To my knowledge all of the 4 pin relays in these cars are 30A relays. There is one 5 pin relay under the hood which is the 1st relay among the group of 7 under the hood in my 94 but Im not sure what is the required Amps on that one
Someone else here with more car electrical knowledge can speak to the Amp requirement of these relays. I researched the numbers on the original Hella relays and found out that they were 30A. I like the see thru though..here is a link to the Bosch relays if these are too cool looking for some people.
Don, I'll definitely be doing some research to see if the original relays had this clamping circuit. Given the price I paid, I sure wouldn't expect the new ones to. This is good advice, and I appreciate it. I'll be checking this out
g7162002, It sounds like you and I are in much the same boat. I'm a pretty capable (albeit shade tree) mechanic, but this is my first foray into the Jaguar world. These cars are different, but not necessarily difficult once one takes a moment to process it.
As for the 60A relays, I did select them intentionally. Since they aren't functioning as an overcurrent device, the extra load carrying capacity is really just "overhead," and it means that these things just won't have to work quite as hard to perform the same task. It's the contacts that get the amperage rating, so running 40a through a 30a relay for example will burn the contacts and cause premature failure of the relay, rather than perform any kind of safety function. Here, we have (less than) 30A being passed through contacts rated for 60.. With any luck that means these things will outlast the car.
In other news, this fix does not appear to have resolved my own intermittent start issue, but I think that's another thread at this point..
But I see it says 60A. My father was electrician and he always preached never to put a bigger circuit breaker in other than what's required because you could burn a house down in that the breaker/relay would not trip and cut the power if need be. Therefore, possibly burning something up. To my knowledge all of the 4 pin relays in these cars are 30A relays. There is one 5 pin relay under the hood which is the 1st relay among the group of 7 under the hood in my 94 but Im not sure what is the required Amps on that one.
Hi g7162002,
Just to add to Mike's reply, relays are not like circuit breakers or fuses, which must be sized to protect other components in the circuit. A circuit breaker or fuse that allowed too much current to flow in a circuit could allow other components to be damaged.
A relay is just a switch, which allows a low-current circuit to control a higher-current load circuit. The amperage rating is the maximum continuous current the load contacts can handle without being damaged. So as long as a relay's coil didn't require excessive current to close the load contacts, and as long is it would physically fit, a relay rated for 1,000,000A could be used in a Jaguar.
My recollection is that not all XJ40 relays are rated at 30A. I think I remember that the fuel pump relay is rated for 40A, and possibly a few of the others.
05-13-2021, 07:36 AM
Crank But No Start Issues Resolved
