wed3k

Ive been trying to fight this issue on a 92 lexus es300 since April. Initially it would hesistate really bad on the highway and then it wouldnt idle.

this being my dad's car, he opted to change the entire engine out. 22 hours later, a JDM engine was put in. hesistation and misfiring at idle was still there.

list of everything that was replaced
-optima battery
-alternator
-JDM engine
-jdm distributor
-Cap
-rotor
-plugs
-plug wires
-any hoses that were cracked
-all o2 sensors
-fuel filter
-air filter
-transmission fluid
-transmission filter
-oil and filter
-jdm fuel injectors

The engine idles well and never dips below 750 but at idle you can feel it miss and the tail pipe indicates a lean condition. Went to the smog station and they put the sniffer in the tail pipe. At idle it will be around 400-500 ppm's but I also saw it jump towards 900ppm for HC's.
CO was always below .5% and NOX was zero.

at 15mph and 25mph it will pass no problem (30-40ppm for HC)

Im leaning towards a vacuum leak but i sprayed half a can of carb clean all over the intake manifold, all vacuum lines and hoses, all the way down to the charcoal canister and the idle never raises...At idle, it will read 18in-hg but will fluctuate a bit.

Ive done a compression test on the front bank because i thought there was an issue with the number one cylinder and the front bank read 100psi across the cylinders. spark plugs look good.

Im about to throw the towel in and my only possible solutions are looking for a smoke machine to find a leak or i wired one of the vacuum lines wrong.

SK1

100 PSI sounds low for compression. Was the test done with all spark plugs out and the TB open with a strong battery? (I use another car Idleing as a Jumper)

Define tail pipe indicates a lean condition.

And please do look into the smoke machine!

Also what size are JDM Injectors vs. US Spec? I'm assuming they're the same......if they aren't and you're using US spec electronics you know the deal...lol

wed3k

yea i was wondering the same thing because i used that gauge on a honda accord with 8.8:1 compression and it registers at 175psi.

i only took the front bank's spark plugs out. car was warmed up already, TB wide open and it would crank all day long if it had to. the reason why Im not tripping is because it was 100 solid across the three cylinders.

tail pipe was clean with a slight brown tint and high HC usually means rich however the tail pipe and plugs were clean which is why im leaning towards a lean misfire.

As for the injector flow rate, im not sure but ill do some research. I know that they are high impedance injectors.

GEORGE_JET

100 is far too low for the compression. I would strongly recommend pulling the rear spark plugs, (along with the front plugs) so that the engine will crank faster. Then take another reading, on all 6 cylinders. If you do not get somewhere near 180 psi, then the next step would be to check the timing belt. The belt may be one tooth off, and also check valve clearance. The low compression is a problem, and you must find out why it is so low.

I am a little surprised that you are having a issue with a JDM engine, I have installed several without issues, but I guess there is always a first.

llcoolpass

5 jjumps of the needle and it only goes t o100? are u 100% sure u didnt drop the gauge

GEORGE_JET

Good point, I wasn't even considering that possibly the gauge is hosed. Very strange that all three front cylinders are close to the same low number. I would have to agree that he should check the gauge before looking at the engine any closer.

wed3k

ill check the gauge out but yes i did around 6 cranks for each front cylinder.

if the belt was a tooth off, it would be next to impossible to set the ignition timing. i did have it set with the te and e1 jumped.

GEORGE_JET

if the belt was a tooth off, it would be next to impossible to set the ignition timing. i did have it set with the te and e1 jumped.[/QUOTE]

You are mistaken on this assumtion. The distributor is driven off the rear cylinder bank. You have low comression on the front cylinder bank. There is no reason that one bank could not be one tooth off, while the other is set properly. One other consideration is that these engines have dual overhead cams. It is possible that one cam is off (if work has been done recently). Without knowing the history of this engine, you need to check everything.

At this point, I still recomend verify that the compression gauge is good, and then finding out why the compression is so low.

llcoolpass

yeah buy another gauge, test the "front" cylinders in cold engine condition. if you get 100 again there is something massively wrongwith your engine [head gasket most likely unless you did something else like tinker with the camshafts which for most people on here the odds of that are incredibly low]

wed3k

thats a very good point, i didnt know that. the engine hasnt been touched from the jdm supplier but as far as the misfire, there isnt any leaks and it doesnt consume liquids.

it's been raining lately so I have been procrastinating on the compression test.

llcoolpass

i hope it stopped raining. was it your gauge? if not, then the timing of the valves is a huge suspect next [like one tooth off]

wed3k

sorry but i finally got some answers.

i rechecked my spark plugs and one of them had cracked porcelain and my number 4 cylinder has about 90psi but every other cylinder has 160-175...

car runs a lot better but still misses when fully warmed up (like 25 minute commute). going to go pass smog this weekend.

GEORGE_JET

Check the valve clearance on #4, chances are there is not enough clearance. With the compression that low, the chances of passing emmision are not very good. Since it is on the front bank, access to adj the valve will be very good.

mmlex1987

I have to ask... Was a replacement engine really neccessary?

llcoolpass

george jet, why would a jdm engine need a valve adjustment so bad? they are low mileage.

this is weird that the problem is the same for both the usdm and the jdm. why do you tihnk the spark plug was broke in the jdm? was it a denso [oe]?