Sounds good. In that case, warm up the car in your garage, pumping the accelerator as required for the first minute or 2, get it warm so it idles perfectly, then do a snap throttle test - dip the accelerator quickly and let go quickly (no more than one second in total) and check how the engine responds. You will dip it quick enough not to rev the hell out of it, that’s not the aim. The aim is to check the engine responds instantly and without hesitation (deviation or repetition 😀). It shouldn’t really get over 2000 rpm.
And if it performs exactly as normal, back onto the drive and check it pulls forwards, and then with that confidence take it round the block. And if it still performs perfectly, I think you can confidently go and order a new coolant temperature sensor. But if you do have a separate temp sensor for the dashboard (which probably only has a single wire), make sure you order the correct 2-wire sensor that goes to the ECU.
But if it doesn’t work as I’ve described, and it still plays up even when warm/hot, please come back and expand on it.
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When you say unless you accelerate vigorously, am I correct in thinking you mean pump the pedal rapidly up and down to keep it going?
And, if you do that enough, can you get the engine to run better as it warms up, and, if so, once it has warmed up, does it run perfectly well?
If that is the case, I would be suspecting a faulty coolant temperature sensor telling the ECU the engine is hot when it’s stone cold). (The temp sensor that speaks to the ECU, not the one that feeds the dashboard, if you have a separate one.)
Do you have any diagnostic equipment, such as PSCAN, or diagnostic software, that could tell you what temperature the ECU thinks the coolant is at?
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“Am I reading the above correctly that you can’t just swap out the ECU if you think it might be defective and that something else needs to changed at the same time?
If something else has to be changed at the same time can someone indicate what that might be and why please?”
I’m going off my 1996 Rover 100 fitted with the MEMS 1.6, and I’m presuming your versions of MEMS will be the same.
With my car, fitted with the Lucas 5AS immobiliser, if you fit a different ECU, the car will run for 2 seconds and then cut out. So you have to use the PSCAN to program the ECU to the alarm. I believe I have that correct: the temptation is to think you are programming the alarm and fobs to the ECU, but I believe that is not the case - the ECU is matched to the alarm. (I’m sure Mr PSCAN can correct me if that’s wrong.). None of the free diagnostic software packages I’ve mentioned, MEMS Diag, MEMSFCR…., can do this.
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MEMS Diag, that takes me back. I wrote about Pawel’s MEMS Diag app in my first article (attached). Not having any Android devices, I went to great lengths to run it inside a virtual machine running Android on my Windows laptop, and I did use it that way on occasion - it’s still a very attractive app.. It was more of a challenge than a genuine attempt to run the app, and it made me seriously consider getting hold of an Android tablet just for the sheer convenience of holding a tablet, rather than a bulky laptop, whilst sitting in the driver’s seat with the seat pushed all the way back to rest the laptop on one’s knees.
Martin
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That’s kind, but I’m no expert; in fact, I was a bit hesitant to reply. I’ve had a Rover 100 (MEMS version 1.6) for some 20 years. I first came to the T Bar when I bought a PSCAN a few years back so I could add new key fobs. I thought the T Bar only related to PSCAN! But I recently got drawn back to this forum again because I’ve just fitted, with a minor mod to the buzzer, one of Bruce Cotsell’s low-level coolant alarms.
My knowledge is partly from using laptop-based free Rover MEMS diagnostic software over the years. I wrote 2 Car Mechanics articles about this free software, the later one of which should be attached. So that, together with delving into the MEMS systems using my PicoScope, and being a long-term follower of ScannerDanner.com (his premium channel and the Youtube free stuff), is where I’ve picked up my info along the way.
I will try and make a habit of looking in on the forum just in case I can throw in my two-pennies-worth along the way.
Thanks
Martin
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Awaiting, with interest, how you get it back in! Creating a partial vacuum in it, if that’s feasible, for a couple of days, might accelerate that shrinkage everyone claims happens.
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Have you made any progress with this? One thing to point out: the system should go into closed loop a minute or so after start up, as soon as the 02 sensor has warmed up due to its internal heater and the heat from the exhaust gases. The sooner you pull away, the quicker it heats up. And the ~0.49V is a bias voltage created by the ECU that it can use, when the ignition is turned on, to detect a short to ground in the sensor. I’m not 100% certain, but I don’t think that bias voltage allows the ECU to detect an open circuit; however, it does allow you to carefully probe at the 02 connector with the ignition on, engine off, to see if you detect that voltage - if not, you have an open circuit between the ECU and the connector. It won’t be 0.49V, your digital voltmeter will pull it down, depending on its input impedance. That 0.49V bias voltage drops away to zero as soon as the 02 sensor starts to warm up and switch between ~0.2V and ~0.8V, which it should do around once a second.
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I also just fitted one of Bruce’s alarms to my Rover 100 (1996), and, having a conventional front-engined vehicle, I swapped Bruce’s piezo buzzer for a combined light-and-sound alarm (£2 on ebay), which I fitted to the dash, consulting with Bruce beforehand as to the feasibility. I like the fact that, as the ignition is turned on, Bruce’s alarm gives a short beep (or short beep and flash in my case): it’s confirmation to the driver that the circuit is live and functioning.
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