Engine Still Misses After Replacing Ignition Parts

[benscharlotte21]

My motor is still having its misfire issue. The only thing I really have left to replace is a fuel pump, however I have dual tanks and something tells me that both would not go bad at the same time.
Anyways any help is appreciated.

Thanks

 

[350runner]

Can't help with the lift but.... if you've changed all ignition parts and still have a misfire try unplugging your vac advance if the miss goes away then it's your pickup coil that went... I just bout a skip white dizzy cause this test proved right. I'm by next Fri our Sat we'll see

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[benscharlotte21]

It's TBI so I dont have a vac advance

 

[350runner]

But you still have a pickup coil... wonder if there is a way to test it... May be ohms.

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[benscharlotte21]

Im sorry but Im still kind of foggy what youre talking about. I replaced the cap and rotor and all the plugs and wires. What coil should I check?

 

[benscharlotte21]

I found a Duralast pick up coil at AZ for 10 bucks.. part number DR132 is that what youre talking about?

 

[350runner]

If it fits your distributor yes.

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[HotRodPC]

For your miss, eventually you're going to need to quit throwing money at it as in buying parts to find it. If you've done the common needed maintenance and still no change, then it's time to be a mechanic, not a parts changer. Yes, there are ways to test coil pick ups, coils, plug wires and all of that. Of course where in the garage section with a suspension issue and Tie Rod title, and that's not likely to get you some help with this miss.

I'll get this all fixed up and see what we can do to get your miss resolved.

 

[benscharlotte21]

Okay so in terms of the miss Im about to go into great detail here so bear with me...

What it is doing: First it idles around 1200 RPM which seems high. Then, no matter what when no load is on the engine and I am in the cab perating the gas watching the tach, i will build up RPM to around 1800 at which point it will drop to 1500 and continue to do that cycle if I leave the gas pedal where it is. If I continue to push the gas it will rev higher and sound fine after that. Driving wise here is the part that gets me, it does not do it all the time. I often times am driving down the road no problem around 40 miles an hour. At which point, after some time, I can physically feel the engine miss and have just about enough time to say a few choice explicit words before I will get a check engine light which is always a code 44. Another side note the CEL is almost always on if I run on the highway at 55-70mph. Again same code 44 lean exhaust. The truck has actually turned off a few times when I throw it in neutral and coast. Kicker is usually when I turn the truck back on CEL is gone and I have great performance.

So anyways... I got the truck torn apart in July, and spent two weeks rebuilding it back up. Put everything back together and had a solid check engine light that hardly ever went off for about three months. It seemed to run fine and I was still busy fixing everything else that it was on the back burner. Then I came home from college and replaced the O2 sensor. That is right about when it began to act up. I immediately tested the MAP sensor and TPS to make sure they were functional. MAP was fine, TPS seemed a little low on resistance so I replaced that. Next came the fuel filter and wow was that overdue. After no improvement there I checked and cleaned the EGR and rebuilt the TBI unit, throwing a throttle body spacer, new IAC valve, and new injectors in there for poops and giggles. After that didnt work I brought it to someone who had an actual OBD plug for it and when they plugged it in at idle everything seemed fine. It was alternating between open and closed loop and everything looked alright... of course! After that I decided to go after physical ignition pieces themselves, plugs, cap and rotor, plug wires.I think that is all I've done thus far. I should note also that all the vacuum lines are new and that the EGR valve is good and ive watched it move with acceleration, however it really seems like Vacuum has nothing to do with the girl. I can fully depress the EGR valve and it does not effect the idle at all. I can also literally take hoses off too and it does nothing. I have very little back pressure running Super 10 mufflers but I have a few buddy's running straights that don't have this issue.

Anyways I think that is all...

 

[chengny]

Just to recap, basically it is fine at lower speeds 95 percent of the time but as soon as I go 50 after a few minutes at that speed I can feel it miss and sure enough check engine light comes on.

Have you looked at your exhaust system?

•Check for an exhaust system restriction:

1.With engine at normal operating temperature, connect a vacuum gage to any convenient vacuum port on intake manifold.

2.Run engine at 1000 RPM and record vacuum reading.

3.Increase RPM slowly to 2500 RPM. Note vacuum reading at steady 2500 RPM.

4.If vacuum at steady 2500 RPM is more than 3" lower than at 1000 RPM, exhaust system should be inspected for restrictions, see Restricted Exhaust System Check.


Here's an easy check I do on turbo-charged engines that suddenly lose power with increased speed/load (without any other obvious problems).

Just pull the O2 sensor. This will provide an outlet for excessive back pressure in the exhaust piping. Take it out on the highway and apply a heavy load to the engine. If performance improves dramatically, open and inspect the exhaust system for restrictions.

Do you have catalytic converters installed?

Never mind - you posted the above while I was writing this.

 

[HotRodPC]

We need to get Jims86 in here on this one. He's one of the resident TBI gurus. This could even be an IAC or other part. Could possibly even be an EGR issue. So chill on just buying ignition parts unless you know for certain it's time to replace them anyway and want to just for the maintenance factor cuz I doubt any of those parts are going to fix this issue and it will be related to the CEL light too. Chances are you get the CEL issue resolved, your issue that you're calling a miss will be resolved too.

 

[HotRodPC]

and I was about to mention chengny will prolly show up with some literature too.

 

[benscharlotte21]

Yeah exhaust back pressure is definitely not the issue that I can say with confidence lol. Are these TBI systems typically not very vacuum oriented?

 

[benscharlotte21]

Also Im correct in my thinking that each fuel tank has its own fuel pump? And that that is likely not the issue seeing as it does it the same amount on either tank

 

[chengny]

No worries I'll try and find a pressure gauge and test that

How did you make out on the fuel flow and pressure tests?

Did you do a thorough inspection of the fuel lines - particularly the common line from the tank switch valve to the throttle body? Looking for kinks, pinch points, etc?

Any chance there might be an old, long forgotten, fuel filter in the supply piping?