RGK20m3

Anyone know if the lower plenum and trumpets are the same between these? The upper plenum is of consistent height on the 4.0, which probably would allow the trumpets to all be the same height. Thinking of putting a 4.0 upper on a 3.9 lower, just wondering why LR made the 4.0 different.

Installed a Ford TPS; electrically it is close, about .4v was as low as it goes. I set it up at .41 with throttle closed, which it now gets consistently. Solved all of the issues- I think on mine it was trying to relearn idle at each stop. Installing it required a little fab work. I installed it outboard on the bracket for the cruise servo/ throttle cable and devised a drive adapter.

I pulled the plenum without disturbing theTPS; I measured the throttle blade and it was perpendicular within about .005”. Measuring the TPS resistance on the bench did not give a consistent value, sometimes was 1080 ohms, other times 1320 or in between. It also would sometimes drop a few hundred ohms right off idle when the throttle was opened slightly. Correcting the throttle stop so the blade was exactly perpendicular made no difference. With TPS off of the plenum, I couldn’t get a consistent reading in the closed throttle position, although the readings were 625-800 ohms. I think that confirms the TPS is junk. Now I have to come up with an alternative….

I know it is too high; I set it there because I disabled the idle air motor and speed sensor.

To pinpoint what component is acting up, I disconnected the speed sensor and idle air motor, then set base idle to 800- still had the issue so scratched those two off the list. I have come to the conclusion that the problem is with the TPS; I did an ohmmeter test on a cold engine and noted the there was a decrease in resistance off the idle measurement as the throttle moved, then the normal increase as the throttle opened more. I think the refresh rate of Rovergauge is slow enough that I couldn’t see it. At any rate, I loosened it, jiggled it around and found a spot where it didn’t seem to act up. Runs fine right now. Now I need to figure a way to install a GM or Ford TPS, because $300 is ludicrous for a $25 part. Thinking the GM might be the better option, as the V6 has the same rotation direction as the Rover.

I’m thinking so, although not that old and genuine AC Delco. I might try setting the idle air bypass screw to support an 800 rpm idle with the idle air valve fully closed, and then unplug it. If it seems ok that way it would indicate a bad idle air valve. If it still acts up, either TPS or air flow meter.

Has done it with 3 different AFMs, and every time that I have checked it, I have a speed sensor reading on Rovergauge. Doesn’t mean either of those parts are not intermittent though. Need to get a new battery for the laptop to monitor while driving I guess.

Well, it hasn’t done the cold start stumble since I switched to a non-catalyst/non-oxygen sensor map (EEPROM is a modified R3652 map), but has a new issue of stalling as I come to a stop warm. Also, occasionally the idle will not stay at the 1000 rpm as I coast down to 2-3mph. I am starting to think the idle stepper or TPS……makes it hard to drive as it is a stick.

I hear you on the injectors; when I rebuilt the engine I had the OE injectors serviced- one was deemed bad and was replaced. Ran great for a few days, then was hard to start hot and idled rough. Sent the injectors back and 3 were deemed bad…. I then replaced them with a reconditioned set of Bosch (a Ford V8 application) and haven’t had any issues that I could blame on injectors for the last few years. No remapping for the new injectors, though. I would be happy if I could solve the cold stumble/no throttle response, the rest of my observations do not appear to affect performance. Might be addressed with an adjustable fuel pressure regulator, it seems the pressure might be a few psi high.

TPS on mine is non-adjustable, and I measured the signal at closed throttle (.36v), and it moves smoothly up to 4.8v. Also confirmed on Rovergauge that it progresses smoothly from 5% to 100%. My understanding is that the ECU will adapt to any idle TPS reading below .545v on a ‘95. I had replaced it maybe 10k ago when I rebuilt the engine. Both oxygen sensors were also replaced about 10k ago, and they both switch according to Rovergauge. I am leaning towards ignition but would like to confirm something before throwing parts at it. It has a Powerspark distributor with a Lucas module (on the body), along with the Lucas coil recommended. Powerspark ignition wires also.

Only other thing that I noticed is that while driving, the TPS was now showing zero at closed throttle; I do understand that the ECU adapts to the closed throttle reading. Is this done every key cycle? Or every time it is at idle for a period of time? I do see that while driving the target idle is achieved consistently, although the stepper will vary , sometimes zero and sometimes as high as 6%. Also both O2 sensors cycle around the center while driving but are constantly below center at idle- no idea why the long term is at -100% on both. I wonder if a small air leak before the O2 sensors would account for the long term trim issue? It has no misfires, has headers, no audible leak before the sensors.

Has not acted up the last 2 days; drove it a few miles with the Rovergauge on, everything seemed plausible. Will keep trying with timing light on coil wire to see if ignition is dropping out.

Would make sense. Didn’t act up today, will try again tomorrow.

I’m kinda thinking the same thing. This morning I am going to leave the fuel pressure gauge on it and hook an inductive timing light on the coil wire, that way I can see if either fluctuates while the problem occurs- which it should as the ambient in the garage is the same as yesterday. Loss of ignition due to the amplifier would interrupt the injectors, which would explain why there is no backfiring…..just wonder why Rovergauge doesn’t show it. Only thing it shows is the idle stepper compensating for the drop in rpm,slight change in the AFM. I don’t think the tach signal drops out, just in response to the lower rpm.

Starts normally hot or cold, and idle is about 1000 rpm, then drops down normally. After about 30 seconds the engine will shudder and immediately smooth back out; it will do this 4-5 times, then runs perfect. If you try to accelerate during the shudder it won’t rev or accelerate, and sometimes will stall. Starts right up again, but won’t rev above idle. I had Rovergauge on it today while it acted up, injector pulse width didn’t change (4%/2.9ms), fuel pump indicator didn’t drop out, TPS didn’t change (6%). AFM stayed steady around 28%. Engine temperature had started to rise slightly from the 40F ambient, fuel temperature was still 40F. Fuel trim was jumping from center to -20% both banks (long term is -100% both banks, but runs great hot). Only faults are 44 (left o2) and 23 (low fuel pressure). Fuel pressure gauge on it after it was warm showed a steady 30 psi, rising to 38 with vacuum disconnected. Any ideas?