88 XJS High fuel pressure, I think it's running rich
#21
08-17-2020 | 06:26 PM
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Thanks again Grant, and everybody else.
Turns out an OEM left-hand FPR did wonders... We are not home free yet, but the pressure is down to 40 PSI before the regulator, and the car is running much quieter and is much more peppy. There is still a slight "two stroke" sound to the exhaust. I'm going to see if I can't flush or just replace the fuel return line, and go from there.
Other things I've checked, the coolant temperature sensors. What I read says there should be two, one on each bank. The left hand one on my car has two leads and it's reading 0.5 volts after a short drive, car is definitely not up to temperature, and what I'm reading says it thinks the temp is over 100C. I'm guessing that one is a dud. The right hand one only has one lead... Weird... But I measured between that lead and ground, 1.6 volts which is around 60C which seems right. I might just go ahead and replace both anyways.
My car seems to have a third, one that is in the radiator. This is an aftermarket "Cat Cooler" radiator I believe, definitely not the original one. There are two leads going to that, but a previous owner has shorted them together -- the only thing I can tell is those leads wire up to the e-fans, and defeating that short keeps the fans off. The sensor always reads an open circuit no matter what, so I think it's dead either way. Is this a standard sensor that I don't know about? I have not read anything about it in any documents or anything.
I cleaned all the grounds I can find in the engine bay and cleaned the power resistor leads, they seemed fine but it definitely didn't hurt.
I'll look into getting the cooling system up to snuff, it seems to have been pretty well taken care of, but given the state of the fuel regulators and the coolant temp sensors, that's not good for much.
Turns out an OEM left-hand FPR did wonders... We are not home free yet, but the pressure is down to 40 PSI before the regulator, and the car is running much quieter and is much more peppy. There is still a slight "two stroke" sound to the exhaust. I'm going to see if I can't flush or just replace the fuel return line, and go from there.
Other things I've checked, the coolant temperature sensors. What I read says there should be two, one on each bank. The left hand one on my car has two leads and it's reading 0.5 volts after a short drive, car is definitely not up to temperature, and what I'm reading says it thinks the temp is over 100C. I'm guessing that one is a dud. The right hand one only has one lead... Weird... But I measured between that lead and ground, 1.6 volts which is around 60C which seems right. I might just go ahead and replace both anyways.
My car seems to have a third, one that is in the radiator. This is an aftermarket "Cat Cooler" radiator I believe, definitely not the original one. There are two leads going to that, but a previous owner has shorted them together -- the only thing I can tell is those leads wire up to the e-fans, and defeating that short keeps the fans off. The sensor always reads an open circuit no matter what, so I think it's dead either way. Is this a standard sensor that I don't know about? I have not read anything about it in any documents or anything.
I cleaned all the grounds I can find in the engine bay and cleaned the power resistor leads, they seemed fine but it definitely didn't hurt.
I'll look into getting the cooling system up to snuff, it seems to have been pretty well taken care of, but given the state of the fuel regulators and the coolant temp sensors, that's not good for much.
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Greg in France (08-18-2020)
#22
08-17-2020 | 08:54 PM
Joined: Feb 2010
Posts: 27,809
Likes: 10,607
From: Adelaide Stralia
Spooky,
Good news on the FPR.
That "stroking" is possibly more to do with spark plugs, gaps not set at 0.025", timing, maybe a tad advanced, TPS and butterflies need resetting, or most likely, it needs a GOOD HARD DRIVE. Idling around with these engines is a no no.
The temp sensor on the B bank is the ECU sensor, and it has a reference volts of 5V in one wire FROM the ECU, the 2nd wire is the signal TO the ECU, to tell is what to do as far as fueling goes. There is a chart for resistance at ?? deg, but I dont have it at the moment, and thunderstorms outside, I am staying inside.
The sensor on the A bank is for the Gauge.
Radiator sensor, NOPE.
I seriously doubt the return line is giving any grief.
That cooling system "sticky" will walk you through the maze. It is a simple system, just different.
Good to hear you did the earths, and I assume you sorted the engine earth fiasco at the LH engine mount, if not, you are in for an adventure, HA. Or do what I do, one dedicated earth strap, engine to chassis, jobs done.
Good news on the FPR.
That "stroking" is possibly more to do with spark plugs, gaps not set at 0.025", timing, maybe a tad advanced, TPS and butterflies need resetting, or most likely, it needs a GOOD HARD DRIVE. Idling around with these engines is a no no.
The temp sensor on the B bank is the ECU sensor, and it has a reference volts of 5V in one wire FROM the ECU, the 2nd wire is the signal TO the ECU, to tell is what to do as far as fueling goes. There is a chart for resistance at ?? deg, but I dont have it at the moment, and thunderstorms outside, I am staying inside.
The sensor on the A bank is for the Gauge.
Radiator sensor, NOPE.
I seriously doubt the return line is giving any grief.
That cooling system "sticky" will walk you through the maze. It is a simple system, just different.
Good to hear you did the earths, and I assume you sorted the engine earth fiasco at the LH engine mount, if not, you are in for an adventure, HA. Or do what I do, one dedicated earth strap, engine to chassis, jobs done.
Last edited by Grant Francis; 08-18-2020 at 03:07 AM.
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#23
08-18-2020 | 12:56 AM
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Joined: Jan 2012
Posts: 13,632
Likes: 9,478
From: France
The rad sensor is a non OEM thermostatic switch to trigger the electric fan. If the PO joined the two wires, then, if I am right, that should mean the electric fan runs whenever the car is running. If you would like to control the electric fan as OEM, when the inlet temp to the water pump reached 85 degrees C, place a suitable thermostatic switch into the rad, or use the one that should still be in the water pump inlet spout.
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#24
08-18-2020 | 12:50 PM
Senior Member
Joined: Apr 2011
Posts: 321
Likes: 162
From: Iowa
I picked up an 88 XJS a few months back, and it's developed some issues recently.
When it started was about a month or two back. I had only driven it for maybe an hour at a time at this point. I took a 4 hour roll around the highways, and noticed that it was running a little differently by the time I got back to town, couldn't place why. Then, ever since, it's been a bit more rumbly at idle, and will hum quite ferociously between 1000 and 1800 RPM no matter the gear. Also seems to have a bit less go juice in those revs than before.
Since then, it has been hard starting about half the time from cold, and occasionally when hot, where it would not have any problems starting before this.
What I know is that it is *louder* and less peppy than before. There is some soot in the exhaust, but not much and I admit I wasn't clever enough to check that before I bought the car. The fuel rail pressure have been around 50 since this fiasco started.
What I think is that it's running rich because of the high fuel pressure. I've read that it's supposed to be around 34 and I'm way out of that range.
What I have done was replace both fuel pressure regulators. The old ones still worked in that if I removed the vacuum, the pressure went up even more, but I smelled some gas in the vacuum line and just went ahead and replaced them. Not sure if that was a good idea or not in hindsight, the rail pressure is still around 48 when idle and 46 when hot. The new regulators also appear to work, since again removing the vacuum makes the pressure go up. I have also check the return fuel line and fuel seems to flow, I disconnected the return to the gas tank and let it flow into a can.
I have had no stalls at any point, it does any speed I ask of it with no problem, but I am dead certain the cat is not running right.
Cheers if anyone can help me out here
When it started was about a month or two back. I had only driven it for maybe an hour at a time at this point. I took a 4 hour roll around the highways, and noticed that it was running a little differently by the time I got back to town, couldn't place why. Then, ever since, it's been a bit more rumbly at idle, and will hum quite ferociously between 1000 and 1800 RPM no matter the gear. Also seems to have a bit less go juice in those revs than before.
Since then, it has been hard starting about half the time from cold, and occasionally when hot, where it would not have any problems starting before this.
What I know is that it is *louder* and less peppy than before. There is some soot in the exhaust, but not much and I admit I wasn't clever enough to check that before I bought the car. The fuel rail pressure have been around 50 since this fiasco started.
What I think is that it's running rich because of the high fuel pressure. I've read that it's supposed to be around 34 and I'm way out of that range.
What I have done was replace both fuel pressure regulators. The old ones still worked in that if I removed the vacuum, the pressure went up even more, but I smelled some gas in the vacuum line and just went ahead and replaced them. Not sure if that was a good idea or not in hindsight, the rail pressure is still around 48 when idle and 46 when hot. The new regulators also appear to work, since again removing the vacuum makes the pressure go up. I have also check the return fuel line and fuel seems to flow, I disconnected the return to the gas tank and let it flow into a can.
I have had no stalls at any point, it does any speed I ask of it with no problem, but I am dead certain the cat is not running right.
Cheers if anyone can help me out here
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