As most of you know, my GEMS P38 runs on LPG. Unlike the later multipoint systems it has a single point so LPG enters just before the throttle body and the output from a lambda sensor adjusts a stepper motor valve in the LPG feed to keep the mixture correct. Because it doesn't slave off the petrol system, it can run on LPG from stone cold. It is set to change over at 1,100rpm on deceleration which means it starts on petrol, the revs rise initially and as they fall, it changes over and runs on LPG from that moment onwards. I keep some petrol in the tank for starting and in case I run out of LPG. Which I did a couple of days ago. My local Flogas charges 78p per litre and the two other filling stations nearby are £1.05 and £1.09 so I try to avoid them. I ran out of LPG a couple of days ago, so ran on petrol to Flogas but was too late, they had just closed. As I needed to use the car that evening, I bunged £20 of petrol in only to find it runs like a dog!
The idle on LPG is perfectly smooth but on petrol it is lumpy, accelerating up a slip road it could only just hold the same speed rather than accelerating as it would normally so seems down on power, although once I had got it up to cruising speed it felt normal. As I stopped at a roundabout, it stumbled and died but restarted without problem. The lumpiness clears once the revs are up to 1,000 rpm or so, so it is primarily an idle problem. As idle is controlled by the idle air valve, I gave that a clean (but thinking about it, that is still used when on LPG where there isn't a problem) and the petrol filter was replaced about 10k miles ago (I bought it when I first got the car 13 years and almost 300k miles ago and found it in the garage recently so decided to change it as I could). There is a separate 0-1V lambda sensor in the right bank exhaust downpipe solely used to drive the LPG system so the only part of the petrol injection system used by the LPG install is the throttle position sensor and that is only used to shut off the LPG on the overrun.
When running on LPG the petrol injectors are switched off but the fuel pump stays on and just circulates the fuel back to the tank. On petrol the RH bank lambda sensor switches as it should but the LH bank one stays pinned at 5V suggesting a lean mixture, yet the exhaust smells rich. Which means the only thing left would appear to be the injectors. My theory is that one of the LH bank injectors is partially clogged so the exhaust on that bank is showing as lean, the ECU is richening the mixture (Nanocom shows short term fuel trim on that bank pinned at +38.5%) but not all are getting their full quota of fuel so some cylinders are running lean while others are running rich. Hence me thinking the injectors could do with a clean. So the question is, has anyone used an injector cleaner, which one and did it make a noticeable difference? Or do I need to strip the injectors off and clean them for the rare occasion I actually run on petrol?