Bad Performance of V6
Submitted: Monday, Jan 02, 2006 at 13:02
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Sir_Gibbo
This is my first posting, I was wondering if anyone can shed light on my problem.
I have a 1991 V6 4 Runner dual/ fuel which does not go to
well when running on petrol, its OK on LPG, but has a real problem exceeding 3000rpm when on petrol, is sluggish, missfires a lot and has no power, if you persevere and keep the gas pedal down to the floor, it leaps into life again around 4500rpm (not that there is much left that high up the rev range ) Low end grunt is also lacking on petrol. I have played around with the air flow sensor & it has improved somewhat, but compared to running on LPG its gutless. The motor has just been rebuilt to gas specs.( valve
seat recession caused by the previous owner not ever running it on petrol I recon ) & I have had the LPG system altered to start on petrol, & fitted a Moreys flash lube system to it, but still the problem exists. Any ideas....
Also reading threads on fuel economy of the V6 I have to agree these are thisty suckers, On petrol I get 14.5L/100k country & 17.7 city & on LPG only 19/21 respectively. (on one rather hairy 4 wheel track I managed 32 l/100km, impressed ? )
Still I reckon its a great off roader, haven't found much that will stop it yet.
Reply By: GaryInOz (Vic) - Monday, Jan 02, 2006 at 17:42
Monday, Jan 02, 2006 at 17:42
Any ECU codes??
My theory (FWIW):
Try resetting the ECU, may have gotten itself in a knot. Disconnect the battery overnight and reconnect in the morning. For the next 3-4 tankfulls run on PETROL ONLY. This will allow the ECU to "learn" the operating characteristics of the fuel system/ignition system/emission system on petrol. Most gas fitments to EFI motors have a box (*) that modifies the "point" signal used to fire the ignition coils when using gas.
I'm guessing that what has happened is the battery has been disconnected when they did the installation, and you have used it on gas for most/all of the time the ECU is in it's "learn" mode. LPG burns differently to petrol, and your ECU was inadvertantly callibrated during the learn mode to run on gas instead of petrol (affects ignition timing). Switching to gas switches in the abovementioned box (*) and modifies the timing even further, explaining your poor gas and petrol consumption and poor performance.
Not absolutely sure, but plausible.......
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Follow Up By: Sir_Gibbo - Monday, Jan 02, 2006 at 22:22
Monday, Jan 02, 2006 at 22:22
Good idea except that after the rebuild ( when the battery was disconnected for over a week ) I ran for 1000km on petrol only, so I rekon it should have learnt by then. After that I took the vehicle up to 95 kph then switched over to LPG without moving the throttle, lo & behold it accelerated to nearly 110, so it was definitely running better on LPG.
Before the rebuild & before I started playing around with the LPG system it really was thirsty 25 l/100k so I have improved it a bit.
Found out just before Xmas that the mechanic that rebuit my motor did not clean & recon the injectors, so I think I will do that & see if it all improves petrol performance ( a pig of a job especially the drivers side injectors, but if it has to be done... )
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Reply By: 4runner - Wednesday, Jan 04, 2006 at 17:11
Wednesday, Jan 04, 2006 at 17:11
Hi. I have a 1991 V6 4Runner and find that it is a thirsty little sucker. The best I have had out of it was 12 litres per 100 Km , but on an overall average 13 -14 litres per 100Km is about as good as it gets. Yes, you do have to row the gearbox at low speeds, and on climbing long hills one has to drop from 5th down to 4th. From others I have spoken to about the lack of performance at low speeds , this is normal for a vehicle that weighs in at approximately 2 1/2 tons. Thats nearly 4000 Lbs in Imperial measurement. One thing you should do as others in this
forum have suggested, is to replace the fuel pump and also the fuel filter. Failing that then get the fuel injectors checked and cleaned. But for HEAVENS sake if you have to replace them , whatever you do dont buy the injectors from Toyota, as they quoted me $260 per injector. Multiply by 6 and you will see what I mean. Repco or other good quality aftermarket accesory shops can do better than that in terms of price.
Oh and before I forget, have you checked your air filter element????? Its placed in the most ridiculous position, right behind the left hand head lamp and therfore sucks in every conceivable bit of dust and dirt. A snorker would be a better proposition. Hope that has been of some help.
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Follow Up By: Sir_Gibbo - Wednesday, Jan 04, 2006 at 20:41
Wednesday, Jan 04, 2006 at 20:41
You think 13-14 lt/100k is thirsty, I'd love to get that much.....
I'm lucky to get that in MPG.....
I must add that
mine is a auto so it will be thirstier
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