Hi all -

My 86 SIII was running like a charm for 6 months after I got her and rebuilt the fuel sys (pump, filter, in-line filts, cleaned tanks, in-tank filters). Then one day a few weeks ago, she started to shudder and died on the way to work. Finally got a few moments this weekend to check a few things out. I jumpered white/white-green on fuel relay and pump hummed just fine with ignition on. But in fact pump runs fine with fuel relay in place. Voltmeter on pump shows 12v in both cases. I will book a long block of time and go through all the excellent debug procedures provided on this forum, but wanted to summarize the exact behavior I am seeing in hopes one of the brain trust can give some targeted clues/debug tips.

Full tank of gas
Starts right up after sitting for a few days
Fires up and "runs" but a bit lumpy. Not like she was months ago.
Idles for about 5 minutes or so
Starts to shudder and hesitate
Even applying accelerator does not help much
Eventually just dies.
Attempt to restart fails. Just won't catch and run.
If I go back in a day or so, same behavior repeats

To un-educated me, it really seems like some fuel starvation issue, but odd that it runs OK for a few minutes then just gives up. Pump sounds the same throughout the whole set of cases above. I need to probably get a fuel pressure gauge at the rail to see if it drops or gets erratic at the time it stalls.

Another thing occurred to me. Perhaps this 5 minute or so period is enough to warm the motor up enough such that one or more of the other fuel/ignition system components kicks in or out. Vague statement but I recall in reading that some of these components are time/temp based???

OK thanks lads and ladies - I want to drive my baby!!!!!!!!!!!!!!!!!!!!

Randy in Raleigh

 

The 'could be' list might get a little long, Randy

A few ideas, randomly presented

First, when it reaches the "won't restart" stage, check for spark! If no spark then, obviously, you'll be looking for an ignition fault rather than a fueling fault. (I suspect a fueling fault in this case but you gotta cover the basics just on general principle)

One possibility is the Coolant Temp Sensor for the fuel injection is skewed and over-fueling the engine. A cold engine likes the extra fueling but as the temp increases, not so much. Repeat the start-run-die scenario you've mentioned. Then remove the connector for the CTS and jumper the terminals with a paper clip. Now try to start the engine? Any change?

Check/clean the bundle of ground wires at the rear of the water rail.

Check/tighten the ducting from the Air Flow Meter to the throttle body. Any splits or leaks?

Cheers
DD

 

if black smoke comes out the exhaust when it stutters, it's the AFM.

 

I'm currently cleaning the whole fuel system on my new 1985 XJ6 like you did ( hate rust ! ) so I've been studying everything I can find. Have you tried opening the fuel filler caps when it dies ? I think it's something else like Doug or Jose mentioned but that would make sure it's not just a clogged vent system making a vacuum in the tanks, somewhere I think I read that the pumps can build pressure but don't suck well against a vacuum.

Cheers,
Brian

 

These are the symptoms of a failing coolant temperature sensor which I experienced on an XJ6 Sovereign: if the CTS is faulty it will report that the engine is at full running temperature when it is still cold; the initial starting enrichment will keep the engine running for a specific period but when that cuts off, and if the temperature sensor is not reading correctly, the fuel mixture will be too lean to keep the engine running properly. But once the engine does reach operating temperature, the message being sent by the faulty CTS matches reality and all is well.
it takes only a few minutes to replace that sensor but a check of the wiring and connector first is advisable.

 

Hi Randy,

Some longer shots for you to consider;

How old is your coil? - Check resistance is within acceptable range

Ignition amplifier on the way out (Gets flaky when warm. Ignition shuts off. Let it cool down, all is good until unit get warms again.)

Check resistance of HT leads - uneven readings could be that one or two are breaking down and they all need replacing

Do you sit in traffic jams? Are your spark plugs oiled up and need replacing?

Cheers,

Nigel

 

Hello all -

Could not figure out how to update the posting title to add SOLVED, but indeed I persevered and figure out this issue.

In summary, got the 86 SIII last June and rebuilt the fuel system to get it running, including a new Denso pump. Finally started and ran fine for 6 months, then one day coming up to speed she stuttered, died and would not restart. Towed home and a few days later, she'd start, very roughly, run about a minute or two and then die and would not restart. The brain trust indicated *might* be the CTS sensor which I replaced. Still no luck. I then was removing the wires from the pump so I could apply direct 12v from a jump pack. As I unscrewed the pos term, it snapped right off in my hand... ^!%@%#$I!!!!!

I ordered a new Carter pump this time and re-installed. In addition, I cleaned all the ground (+/-) points but I do not this is relevant.. but you know what they say. As soon as I put the gear in D to prime the fuel rail, I COULD TELL IMMEDIATELY the pump was the issue. This pump hummed so loudly/nicely I could hear it fine and could hear the fuel spinning trough the circuit. Turn the key and she fired right up and 15 minutes later she was idling nice and warm. I drove her out for an hour drive and did not miss a beat.

So here is the debriefing.. when I put in the original new Denso pump, at that time I too could hear it whirring fully and the fuel flowing. But in retrospect, when I started having the issue, I could nt hear it as loudly.. if at all. I SHOULD HAVE not ignored this big clue, but the reason I did is because I initially jumpered the pump to be always on and went back and could hear it spinning so I thought it was OK. So, my first guess is that the pump failed or got damaged with some crud (I did clean/flush tanks last June). It appears the pump was pushing, but not fully, so I had low pressure and maybe when the CTS stopped juicing the system, the fuel input was too low to sustain the motor running.

Yes, I have a fuel pressure gauge and that was long on my list to hook up, but I had lent it to my "pothead" step-son and he never returned and made no effort each time I asked.

So I am happy as a clam and will drive her until the next problem. I also removed the whole smog pump air rail and fixings and put in the plugs in the manifold. I POR-15'd the rusty battery box and the area under the brake booster/resevoir that had leaked at some point. Just ordered parts to freshen the air breather filter and boot.

OK, hope this helps for anyone with my specific symptoms

Randy in Raleigh

PS - No bad words about the Denso pump, but in all honesty, the Carter seems much more ruggedly built, especially the terminals. The Denso ones were rather thin and obviously a reason it snapped. The Carter terminals were beefy and looked like they were anchored into the case. So I would highly recommend the Carter over the Denso and actually cheaper. Rock auto will take back Denso for full refund, so all is good.

 

Not to beat a dead horse, but I have been thinking more abou thtis issue and just wanted to put in some thoughts that might help others who come across this particular problem. I re-considered the symptoms and now, to me, it makes complete sense.

Once the car stopped running, I noticed this pattern:

- Motor was cold
- Would start and run, but very roughly
- Idled roughly for a short period (minute or two ?)
- Listened in the rear and could hear the pump working
- After this short period, motor would stumble and die
- Unable to re-start
- Fast forward to next day or a few days later
- This list of steps repeated itself

So, my non-expert analysis has me convinced that this was why I was seeing these symptoms:
- Pump was "working" but not pushing full fuel pressure. I know that now because of the replacement and hearing it clearly from in the car now
- When motor was cold, the CTS sensor was doing its thing and juicing the intake with fuel
- I *believe* this allowed the motor to start and run roughly, perhaps with the additional "weak" fuel pressure provided fuel from the pump
- The "short period" mentioned above was enough time for the engine to warm, enough to start ramping down the CTS supplied level of fuel
- Eventually the cold start juicing went to a low enough level and the weak fuel supply was not at a good level... and the engine sputtered and died.
- Attempting an immediate re-start was a failure because the cold start juicing was out of the picture and only weak fuel pressure was present
- But, come back a day or so later and try again, then the cold start circuit did its thing and the rough start and die repeated itself.

I did replace the CTS on advice it could be a possible issue. The thought was perhaps that it was NOT kicking off as the engine warmed and TOO much fuel was being delivered. But I don't think that was the issue. BTW, if you ever order a new CTS, they come with two different connector types even though the original site I ordered from said it fit my VIN. I had to go to Welsh, I think, to get the proper one. And going back to the original site I had a laugh when I saw that a couple items lower in the list was the proper connector for the CTS they sold. Apparently they wanted you to cut off the old one from the loom and attach the new connector. Doable, but not desirable.

Thanks for listening and hope this helps someone diagnose a weak fuel pump situation.

Randy

 

I don't know if your 88 has one, but some models had an anti-back flow valve to maintain pressure in the fuel lines. My 86 XJ6 had the same problem that was fixed by replacing the valve.

 

Congratulations on a find and fix. Victory is so sweet.

Thanks for posting the solution. No disappointment from not having the last page.

completes the archives for the benefit of all.

Merry Christmas

Carl