Thread: intermittent problem 92 3.9

Yesterday I tried playing with the idle adjustment with mixed results. Perhaps I did this incorrectly as I probably should have capped the air bypass to the stepper or idle control first. I reverted the settings back to pretty much how they manifested previously.
Today I managed to borrow a working TPS and extended the wiring to suit the Thor manifold setup. On fitting there was no change to idle or operation. On refitting the original I disconnected the battery to clear any ECU fault code and on starting received the 02 code followed by a blank screen on the code reader. Startup gave me the same erratic idle but I adjusted the idle control again and now have a fast idle (950rpm) but no cycling and stalling. This is a little more reassuring. Reducing the idle control in any way reverts it to erratic operation so I will leave it with a high idle for the time being as I can live with this temporarily. Let's see how we fair tomorrow morning with a cold engine.
I will try adjusting idle with the air bye pass to stepper/ICV capped next weekend as I have run out of time again for now.

I removed the plenum and upper inlet manifold over the weekend to educate myself and 'learn' about the system setup and look for potential vacuum leaks. There appeared to be an extraordinary amount of silicone gasket sealer on both sides of the tin gasket, presumably when it was put back together after the cylinder head gasket job. Is this normal? I am hopeful that none fell into the inlets as I removed the excess. How damaging would this stuff be to a running engine if I did get some in there?

I also found a relatively large quantity of oil in the plenum/upper chamber I presume from the PCV. I cleaned all pipes, joints, and chambers before putting it back together.





I cleaned the tin gasket which still had springiness and did not use any gasket sealer in the rebuild. I will take it apart again at some point in the near future to do the job properly and torque the bolts correctly.

The reason for the strip down was that in swapping the TPS over, and adjusting the idle screw, I went from a stalling idle to a large hesitation on open throttle when warm. I wanted to cure all vacuum leaks in one hit and understand the setup and on resolving all vacuum leaks (I capped the downward part of the T-piece as I could not find anything to connect to) and rebuild, I now have no idle off throttle so will need to reset the base idle correctly and sort out the TPS.

I also have an intermittent code 12 (MAF) so will work through the diagnostics with a multi meter this coming weekend. Fortunately I have multiple spare MAF's (3AM & 5AM), a spare TPS and a spare ICV.

So, this weekend I replaced the MAF due to an error code 12. The spare 5AM appears to have done the trick as the code has disappeared although I did not test with a multi-meter.
I did however use the multi-meter to setup the TPS. This now shows 4.7V input, and between 0.325V and 4.9V from closed to WOT. The major hesitation on opening throttle has now gone but I am back to the cycling idle RPM with the engine almost, but not quite stalling.
I did play around with the idle control and the low idle/stall is not quite so pronounced and I can trust the car not to stall at junctions/lights anymore. Interestingly when the car reaches full operating temperature it will maintain idle for short periods, albeit slightly high. There is no real pattern to this yet.
I also attempted to set the base idle by blocking/capping the feed to the Stepper Motor/ICV at both ends but the car would not start at all under these conditions, I presume as there was no airflow and therefore no vacuum leaks, and therefore no ability to idle?
The car is usable again and I will investigate further next weekend.

sounds similar to the problem i have been having with my 93 3.9 Rangie.Will run fine then stall then cough when at over 1500 rpm.go to start it some times and if it doesnt fire first up you have to crank it for a while like it is flooded.but if i catch it fast enough it will fire up on lpg not a problem

2 years on and I thought you might be interested in an update.

I have tried every avenue over the last couple of years, some interventions more expensive than others. I have swapped out almost every sensor one by one, and had a couple of RR specialists take a look with nobody getting to the root cause. I played with the idle, minor adjustments on a week by week basis to assess the impacts. Attempting to set base idle using a couple of methods (capping vacuum hose or unplugging Stepper motor). Interestingly, unplugging the Stepper at its lowest idle level still gave me the cycling from (almost) zero revs up to about 1100 rpm with no stepper valve stepping in ?.

Now today .......

Driving up the pacific highway in traffic. Warmish day and the temperature got over 93C for the first time in a long time. Erratic idle when stationary. Off throttle coming up to a red lights and ..... We had an episode . Engine dropped to a bare idle, would not recover on throttle (felt like it was flooding on any degree of throttle) and we had a stall. Hazards on, bonnet up, checked all hoses and connectors..... Nothing amis...... So I started the engine again......

Perfect .... Steady idle at 680 ish..... No fluctuations, back to normal power, and interestingly the fuel delivery cutoff was very apparent again. The unichip cuts fuel delivery off throttle over 1500 rpm when coasting at a decent speed. So..... I am very happy and very confused. I will keep monitoring the situation over the coming weeks and post an update if things change again.

Leaning towards an interface problem between the unichip and the ECU, triggered/rectified by a short or bad earth somewhere. Unsure why today was any different? Remember that the engine has always been fine off idle and I have done a couple of 500k + trips over the last couple of years with no dramas.

Any thoughts.....?

The unichip cuts fuel delivery off throttle over 1500 rpm when coasting at a decent speed. So..... I am very happy and very confused. I will keep monitoring the situation over the coming weeks and post an update if things change again.

A BLAST FROM THE PAST!
The Unichip does not cut off the injectors, the stock ECU does but it is much more noticeable with the Thor manifold, presumably because there is more torque down low.

Have you replaced the fuel filter ? It sounds like it could be fuel starvation. The fuel pump could also be on the way out, although it was replaced with a Bosch a couple of years before I sold it. Although the fluctuating idle does sound like it could be related to the Stepper, as these are pretty unreliable and also known to get dirty inside. If the little cone sticks it can give the low/high/low /high that you are experiencing.

The car had a brand new distributor ( when LRA was clearing out Classic stock) not long before I sold it to you , so the amplifier should not be a problem, although anything is possible .

Really one of my objectives with the conversion was to use as many 14CUX sensors as possible so that there would be no problem with parts, so the troubleshooting should be as per a 14CUX. The MAF, TPS, Fuel pressure regulator, temperature sensors , and stepper are all 14CUX.

Perhaps go through the tedious troubleshooting procedure for 14CUX as in the manual.

Regards Philip A

Originally Posted by PhilipA

A BLAST FROM THE PAST!
Really one of my objectives with the conversion was to use as many 14CUX sensors as possible so that there would be no problem with parts, so the troubleshooting should be as per a 14CUX. The MAF, TPS, Fuel pressure regulator, temperature sensors , and stepper are all 14CUX.

Perhaps go through the tedious troubleshooting procedure for 14CUX as in the manual.

Regards Philip A

Thanks Phillip. Fuel system is suspect (normally takes 6 or 7 cranks before it starts. Occasionally 3 or 4 - go figure) but remember the car is fine off idle. I would have thought a recent trip up Bellbird Hill would have highlighted fuel delivery problems but it went fine ( and back up the climb from Lithgow).

The only thing that I never really got to the bottom of is the T piece vacuum feed intersecting the flame trap to plenum inlet. There is no where to connect the T piece for vacuum..... Nothing on the inlet so I have capped this. As of today Max is running as well as he ever has...