Missfire on cyl 4 - now on 3 & 7, no power

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Bratwurst

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Hello guys, newbie here, and I hope someone is able to help with my engine problem.

97' Expi 4x4, 4.6L with the 2 ignition coils at the front of the engine

It all started with the check engine light and the engine not running smoothly, no power. Diagnosis was misfire on cylinder 4, I then purchased a new ignition coil for the left cylinder bank.

I then took it in and they checked all the cables, cleaned the fuel delivery system, carburetor, all injectors, cleaned and flushed the tank and fuel lines, replaced fuel pump strainer and installed a new fuel filter.

After this was all done, suddenly there is a misfire on cylinders 3 and 7 (!), so on both banks and there is even less power. It is a really choppy ride to say the least. Cables look all good and tightly attached.

Any help is really appreciated and I thank you guys in advance!
 

1955moose

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Electrical items can't be just looked at, they need to be tested with a volt./ohmmeter. Rather than getting into readings, YouTube how! But the fact you paid them and now it's worse, make them fix it right. We here can give you advice, but are you going to fix misfire, or are they.By the way, if you think your SUV has a carburetor, put the wrenches back in the tool box, and make an appointment with a quality shop! And by the way, who is they?

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Bratwurst

Bratwurst

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Hehe thanks for the reply. I have not done any work on there myself, I admit being not talented enough.

I am living in the Philippines currently and it's extremely difficult to find someone half-trustworthy here, who also knows what they are doing, I went with a repair shop that looked ok-ish and have to make do with what I got. I'm aware that they are trying everything to prolong things and yes, I have paid them already and it did indeed get worse and more complicated.

I am posting here out of desperation, in order to point them in the right direction and finally move on to a more trusted place. As you said, they should be the ones fixing the problem but it appears that they just don't have what it takes to figure out the actual problem with the car.

Going back to the actual problem, I did not find anything on Youtube, or rather don't know what to search. Would you recommend testing all spark plugs with an ohmmeter? Sorry for being so stubborn, your help is greatly appreciated.
 

1955moose

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Spark plugs are one of the few items that need to be replaced, they can't be tested like other electrical items. I wouldn't change the spark plugs yourself, their very difficult to remove on the rear cylinders on both sides. And due to very few threads holding them tight, you need to know how to torque them down installing them. Not a job for a novice. As far as the coils and wires, an ohmmeter is set to ohms and their specs will vary. If you Google how to test a coil you should get quite a few videos that give specs. You'll only have to test the one that wasn't replaced. From what your telling us, your mechanical ability is limited, so your kinda stuck finding a shop that's better than the one that took your money.=

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Bratwurst

Bratwurst

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Thanks for your reply, 1955moose. So I guess I will go ahead and buy new spark plugs then. The way it looks now, I think that both coils were actually fine and didn't need replacement.

Is there anything else you can think of that might cause these problems?
 

1955moose

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Unless the coils got wet your probably right. I can't tell you how many people came into my store with coil in hand, saying they wanted to buy a new one. I kept a volt/ohmmeter behind the counter to do basic measurements for customer's. Over 90 percent of the time, their coil was good. Turned out to be either the module in/on the distributor, or pick up coil. Unless they leak black ooze or get cracked or really wet, they usually go the life of vehicle. #3, and #7 cylinders are right next to each other in firing order. I would change all 8 spark plug wires with a quality wire, and see what happens before you change the plugs. You probably have a bad spark plug wire.

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Bratwurst

Bratwurst

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Hello again,

it has been an eventful 2 weeks - we have taken everything apart again and checked wires and the (new) spark plugs again. The engine was running fine and the shaking stopped. No more misfire error codes.

During the test drive, a new error code showed up, P0118, which indicates ECT (or CHT) sensor input too high. The ECT sensor has now been replaced, but the light is still showing up and comes with the same error every time.

I have now found out, that the CHT sensor sends data to the PCM, and if the input is too high, the PCM might shut down a few cylinders in order to prevent overheating. The engine was running fine but started playing up slightly again yesterday. It has been dry the week before and we had some heavy rain yesterday, I am wondering if this could be related.

I'm having trouble sourcing a CHT sensor quickly here and we will check the wiring in the next few days. In light of this new error code, would there be something else we could check?

Thanks as always - getting there!
 
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Bratwurst

Bratwurst

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Any advice, guys? Problem still persistent, startup is awful but runs fine when the weather is dry. Engine light is still on with same error.

Thank you
 

Trainmaster

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That truck's getting on in years... and that often means wiring troubles. Check the wiring and plug on that coolant temperature sensor.

If you have a scanner that will read the sensor's resistance or voltage in real time, it's easy. You can read the voltage and twist and fiddle with the wires. Otherwise you're stuck with what your eyes can see. Remove the plug to the ECT and to it's source and look for corrosion. Look for a crimp or a scuff in the wire's insulation between the ECT and its termination. It's very difficult to diagnose an intermittent wiring problem without a scanner.

That sounds like it might be your problem. Don't trust the replacement ECT if it's from China either. They are notorious for being bad out of the box.

Very dirty or old coolant can also cause trouble with sensor readings.

With a scanner, follow the ECT readings compared to intake air sensor readings. You can also heat up the sensor area with a heat gun while monitoring the reading to assure that the sensor and its wiring are okay. That's the easy way to test all that.
 
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Bratwurst

Bratwurst

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That truck's getting on in years... and that often means wiring troubles. Check the wiring and plug on that coolant temperature sensor.

If you have a scanner that will read the sensor's resistance or voltage in real time, it's easy. You can read the voltage and twist and fiddle with the wires. Otherwise you're stuck with what your eyes can see. Remove the plug to the ECT and to it's source and look for corrosion. Look for a crimp or a scuff in the wire's insulation between the ECT and its termination. It's very difficult to diagnose an intermittent wiring problem without a scanner.

That sounds like it might be your problem. Don't trust the replacement ECT if it's from China either. They are notorious for being bad out of the box.

Very dirty or old coolant can also cause trouble with sensor readings.

With a scanner, follow the ECT readings compared to intake air sensor readings. You can also heat up the sensor area with a heat gun while monitoring the reading to assure that the sensor and its wiring are okay. That's the easy way to test all that.

Thank you! Will give this a shot and feed back.
 

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