I’m working on 95 Xjs w/ 4.0L. This is not my car, so my understanding of its history is a story at best. I am also not a mechanic just a glutton for punishment. I have been saved by you all in the past and hoping for some direction.

I was told fuel pump died and engine coolant temp (ECT) was bad. Both were replaced along with new fuel pressure reg. When all said and done, car has misfire at cylinder 3. Codes P0303, P0116, and p1314. I don’t want to throw parts at it with out diagnosis. I’m thinking computer is all that would be left or a broken valve spring? Halp.

Work done so far.
-cleaned grounds in engine bay and right side A-pillar.
-checked engine management fuses.
-inspected spark plugs. They were not wet and looked ok.
-swapped coil with known good coil.
-swapped injector with known good injector (both from working car)
-fuel pressure at 35 psi.
-ran new wires from ECT to power train control module (PCM). Proper voltage and resistance at ECT.
-looked for signs of corrosion at PCM and generally looks good.
-replaced bad plugs on injector harness and checked continuity to PCM it is ok.
-coil harness has continuity but not happy with it. Cyl 2-4 had 7-8 ohms to PCM. I have seen worse with no issue, but ordered plugs and wires to rebuild the harness.

Any ideas?

Thanks in advance!

 

Where did you take the fuel pressure from? I believe the Bosch branded regulator on the car gets it to 43psi.

The p0116 usually points to an easy to replace and cheap to buy coolant temp sensor. LHE1600AA I wouldn't be at all surprised if this sensor is throwing off your car's fuelling map.

I'm also assuming that you're calling the ECU a PCM? Checking for corrosion at the ECU in the passengers footwell is always a good, easy and cheap idea.

 

Hi Vee, thanks for the response!

I'm taking the reading between the injector rail and return line. I like the idea of the regulator. I tried swapping out for a different bosch OEM regulator I had. It came up to 39-40psi, but the stumble is still there.

I think the coolant temp sensor is sorted. The readings both resisitance an voltage make sense. The codes since clear have not come back, however neither has the P0303,...

I took a look at the plugs for the computer, they all look clean. There is no corrosion or bent pins that I could see.

 

Ok, so please let us know the current situation of the problem?

You just mentioned stumble?

 

Car has no codes of any kind, but there is a miss. If I remove the connector from cylinder 3 coil, there is no difference in running condition. It’s most noticeable when there is a release of the throttle. Engine hesitates as if it will die and then poor idle returns.

I’m going to try to borrow a smoker to test the intake for leaks. Still waiting on electrical plugs to make a coil harness.

 

Have you cleaned the throttle body? The butterfly commonly gets gunked up. To do a proper job, take it off the intake and clean both ends,

 

Vee
Do the 4 litre cars have coil on plug? If so a duff CoP is a possibility too.

 

Greg,

These engines do indeed have the coil on plugs. The OP says he doesn't want to throw parts at it, and he did already swap the #3 coil with a known good coil, I would cross coils off the list....at least for now, especially since the codes have all cleared, specifically the p0303 code.

If we wanted to throw a part at this, a very costly TPS might be the way to go.

 

Cylinder Compression??? Just a thought.

Jack

 

Thanks for the help all.

Checked compression, 1-6 was 124,130,130,121,122,130. I think that is for 30 yrs old?

When I took the air intake elbow off to get to the throttle body, I found an obscene amount of jb-weld to plug a pinch. I am going to order a replacement elow and gasket for the throttle body. Plugs for for new coil harness get here tomorrow. I'll let you all know what happens.

 

So wanted to give an update and thank you all for the ideas. Vee you're a mensch.

It's all fixed, but good lord was that a bear.

Problems boiled down to two bad injector masked by poor wiring. Once I replaced the coil harness and made sure the connections to the injectors were solid the car was diagnosable. Two of the injectors ended up having no spray pattern. The spray pattern was identical to a dribbling garden hose.

If there is any lesson to be learned from this check the wiring really really carefully. If anything seems bent or work was done take your time with a multimeter, back probe and test continuity/resistance for everything.

 

I do the best I can.

 

Dear Mr. Vee. Where are you on this planet? Anywhere near Philadelphia, PA?