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Fuel Trim Issues

posted Jun 04, 2016 18:09:06 by Blake Soper
I've recently had two family members cars - a toyota and a scion have no codes and no driveability issues with high (20%+) fuel trim lately. High fuel trim at idle that gets better with some throttle. both cars passed o2 reaction tests and vacuum leak water tests.

Any suggestions on what to look for next? I was thinking of maybe the issue is the beginning of low fuel pressure or dirty injectors. Haven't had chance to check fuel pressure yet but that is where I want to look next.
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9 replies
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Dylan said Jun 04, 2016 20:11:23
High fuel trim at idle that gets better with some throttle


So fuel trims get better at higher rpm? How much are we talking about?
Belgium, Europe
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Blake Soper said Jun 04, 2016 20:44:04
20 percent at idle and immediately to 3 percent with throttle.
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Tyler said Jun 04, 2016 22:41:42
What models of Toyota and Scion do your family members own? I ask because there are some engines that are more susceptible to injector issues than others.

I suppose the trims could be indicative of a fuel issue, but I'd expect it to get worse while driving. Checking fuel pressure isn't the easiest job on most Toyota's, unfortunately.

Any chance you could post the scan data at idle? I was interested in checking some other PIDs, like Load and ECT.
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Blake Soper said Jun 04, 2016 23:14:07
Yes I should be able in the next few days. scion xa 2000. Not a Toyota, i meant Nisson Frontier, 1999.
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Dylan said Jun 05, 2016 11:02:22
20 percent at idle and immediately to 3 percent with throttle.


Pretty big difference.

I suppose the trims could be indicative of a fuel issue, but I'd expect it to get worse while driving.


Yeah I'm with Tyler.

Yes I should be able in the next few days. scion xa 2000. Not a Toyota, i meant Nisson Frontier, 1999.


No problem.
Belgium, Europe
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Tyler said Jun 05, 2016 14:13:54
Yes I should be able in the next few days. scion xa 2000. Not a Toyota, i meant Nisson Frontier, 1999.


Sounds good, thanks sir!
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PaulDanner said Jun 05, 2016 18:01:20
Don't forget about the brake booster. Can't test that with water.
Also the PCM system, especially if the inlet is in front of the MAF like on some Fords.
And if you cannot find anything in relation to a vacuum leak or the above. Then do an injector balance test next and make sure the MAF is clean.
I know the fuel trim numbers improving at higher RPM say otherwise. But those are easy things to eliminate.
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IvanKibuka-Kiguli said Jun 06, 2016 05:07:54
If these cars have MAF sensors, I am not sure vacuum leaks are off the list of possibilities yet...
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AndresRohena said Jun 07, 2016 03:42:55
I remember to see this case with an echo and the problem was the fuel line it was block by something that was on the fuel cant remember right now exactly but disconnect the fuel pressure and put some air pressure whit a nozzle also like the guys here says check vacuum leaks at the maf sensor brake booster line etc.
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