Hi! Brand new member (first post) but have been lurking for a while, learning lots along the way.

I've got an 89 XJ Base, 128K, 5-speed, Renix of course. It's running really rich, almost literally a pile of soot in the tailpipe. Sad, sad mileage, maybe 8-9?

I've replaced the TPS, MAP, and 02 sensor. I've replaced both the front and back vacuum harnesses. I've replaced the fuel pump, pressure regulator, and injectors (with 703s). Put in new plugs, wires, and distributor. Even put in a new fuel filter while I was at it (although I knew that should make it run richer yet).

I put a pressure gauge on the fuel rail and it reads 39 psi with the vacuum hose either on or off the pressure regulator -- no difference that I can tell. I've seen quite a bit about what to do if the fuel pressure's too low, but not so much about what to do if it's too high... I'm running short on ideas.

One clue: seemed like the mileage got worse with the new pressure regulator.

Any wisdom would be great. Thanks much in advance.

 

....... there's no change in pressure when you pull the vacuum? Wow that indicates the regulator or fuel pump bit what is it supposed to be...32 or 42? I think 39 is about right isn't it.. can't remember what its supposed to be but you should check all sensors... could be mat or o2... here's a link check it out http://www.lunghd.com/Tech_Articles/...iagnostics.htm

 

X2 in the o2 sensor.

 

Thanks for the replies! As I mentioned, I already did change the o2 sensor, cuz that was my guess, too.

From what I know, the pressure should be 31 psi with the vacuum on, then jump to 39 psi when I pull the vacuum hose off. Seems clear that high pressure reading is causing it to run rich, but what's causing the high pressure? Did I install a bad regulator? Is there a vacuum leak some other place than the vacuum harnesses? Other likely guesses?

 

Also check your coolant temp sensor. If it's sending a low temp reading to the ecm you'll stay in open loop.

 

That makes a lot of sense (as does Slick761's idea about the MAT sensor). I'll try those next and let you know in a few days what's up. Thanks, all!

 

Check your sensor ground at the TPS harness for resistance. It's the brown with white tracer. It's the ground for the TPS, CTS, IAT, and MAP. If it's bad, the ECU gets really bad signals.

Probe the brown with white tracer with the red probe of your ohmmeter and put your black probe on the negative battery terminal. You should have less than 1 ohm of resistance. If not, we'll go on to the repair. Not hard to do.

 

It tests at 0.3 ohms, but that was an excellent suspect.

 

It sounds like the pump is running like there isn't the vacuum like hooked up so either there is a leak or the vacuum isn't working, aka the piece at the other line of the vaccum. I not too sure what that is called.

 

That's a good one to eliminate for sure. I'm troubled a bit by the fuel pressure with the vacuum hooked up. It should reduce to 31 psi with the hose attached. How much vacuum is on the hose at idle?

 

Jakeshain, that's where my mind went, too. I'm gonna keep checking vacuum hoses until I find a leak or I find a fix from one of these other good suggestions. Thanks.

 

Should be around 18 I believe.

 

Nope. 31 with vacuum, 39 without.

 

He was asking how much vacuum should be present.

 

17 to 21, therefore I stand corrected.