Hello! Recently purchased diamante running very rich, other issues. - Mitsubishi-Forums.com
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post #1 of 5 (permalink) Old 07-27-2018, 07:48 PM Thread Starter
Join Date: Jul 2018
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Unhappy Hello! Recently purchased diamante running very rich, other issues.

Hello there. I recently availed myself of a 1994 Diamante ES with 160k miles on it for the sum of $1100.

That being said it seems to have a few issues.

It does have a slight tick which may or may not be anything to worry about. I can't locate the source by ear but it may be valve train or the very beginnings of a rod knock. It did not present itself when I was viewing or test driving the car before buying it (go figure). It is usually very quiet but sometimes makes itself known when starting cold and then gets much quieter after having run for a minute. I'll post a video at the end of this post and you may or may not be able to hear it.

The main issue I am having right now is that it seems to be running very rich. You can smell it at idle. It's an eye stinging and watering smell and the exhaust tips are covered in soot and there is a noticeable puffing sound and slightly visible exhaust from the muffler (not so much as you could see a discernable color), and it makes more of a growling sound than a stock exhaust maybe should. It does not smell like burning oil or coolant. That being said I don't actually know what a lean running engine sounds like so it might be that also.

It seems to accelerate fine at part throttle, but there is an intermittent hesitation or miss you might say. Full throttle was actually working fine until today when it started to stumble, fall on it's face, and stop accelerating. No check engine light or any other sign of distress though. Before today I didn't feel as much of a hesitation at full throttle and it didn't seem to be lacking in power all the way through the rev range.

I tried replacing the pcv valve, cleaning the maf with electrical cleaner (I think thats what that is attached to the air filter box, doesn't seem to have a map sensor), and cleaning the throttle body and IAC. All that seems to have accomplished is fixing a low idle issue. Still very rich at idle and doesn't go anywhere at full throttle as of today.

If I blip the throttle (video link below) it makes a sucking sound and seems to hang a bit instead of dropping the revs back down like I was thinking it should. I didn't catch it for the video but sometimes I can get it to stumble if I blip the throttle quickly. Also sometimes after a few blips you can smell fuel when standing over the engine.

The strange thing is that there is not check engine light. I know the light works because I started it without the maf sensor connected by accident.

Could it be bad O2 sensors or a fuel pump? Seems to me it wouldn't run rich with low fuel pressure but it would make sense for it to fall on it's face at full throttle.

I'm not very familiar with this car or engine yet so any help is appreciated.

video link:
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post #2 of 5 (permalink) Old 07-29-2018, 09:41 PM Thread Starter
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Not a real active forum? I have a coil coming in tomorrow so I'm going to try that first, and the fuel pump isn't very expensive so that's next. When I've got the coil out I'll also go ahead and take the intake manifold off and check plug wires and plugs.
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post #3 of 5 (permalink) Old 07-30-2018, 11:54 AM
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Ticking noises with mitsu engines quite often suggests a valve lash adjustment is needed. Not sure if that is the case with this engine.

Check the cheap stuff, double check spark gap, replace fuel filter etc.

Your symptoms in general make me think your getting missfire issues (extra fuel being shoved out) but that would normally result in check engine light. So would it running really rich/lean as the O2 sensors should be picking up issues like that.

I'd also probably take apart the whole intake up to the manifold and clean it (throttle body cleaner, maf cleaner etc)

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post #4 of 5 (permalink) Old 08-01-2018, 06:24 PM Thread Starter
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I did clean out the maf and throttle body including IAC and that fixed my low idle issue but it still idles rough. I replaced the ignition coil as the old one was out of spec (.4-1.2ohm mine was 1.5) but that didn't seem to help at all. It still seems fine at normal acceleration and then stumbles throughout the rev range with more than a bit of throttle and falls flat on its face at wide open throttle. I'm not getting any check engine lights or anything. I'm getting terrible gas mileage and it still smells really rich. If the o2 sensors were the only problem, wouldn't it still run fine at WOT on the map? I'll check plugs and wires next but no check engine light is throwing me off. I don't want to just start throwing parts at it like EGR, o2 sensors, ecu, fuel pump etc.
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post #5 of 5 (permalink) Old 08-01-2018, 10:35 PM Thread Starter
Join Date: Jul 2018
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update: I tested my TPS and it checked out fine, however my MAF did not. Following the testing procedure here (https://easyautodiagnostics.com/mits...sensor-tests-1) I found that I have good power, ground, and maf reset signal. When testing the maf signal (3rd wire) I found that I get 0.03-0.04khz and it does move up and down when the throttle is actuated, but only when my negative lead is not connected to the negative battery terminal. The test procedure specifies that the negative lead must be connected to the negative battery terminal when you read the signal. When I connect it to the battery terminal as required by the test procedure, I get no signal (0.00khz) and it does not move when the throttle is actuated. I need to verify from other sources that I am doing the test correctly but I don't know exactly what it means if I get signal only when not connected to the negative.
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