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Discussion Starter #1
I am finally getting to sort this car out. The car runs good under hard throttle but when I am coasting down a hill or running at light throttle the car surges or feels like it is missing. I checked the codes and there were none. I have tried three different computers. They all have the same problem with varying degrees. Also I have a new Mopar stage 2 in the car. It seem to be giving me more boost the more I drive it but I am only getting 11 to 12 psi max at this time with 10 miles on the computer. In the higher gears it shoots up to 10 but drops off to about 8 psi. I have a grainger valve but I want to wait until I have the miss corrected. I changed cap wires plugs and rotor no luck. Any ideas? O2 sensor?
 

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R.I.P Dennis Jarvis
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Have you checked for vaccuum leaks? How about installing the grainger valve to see if the problem goes away.
 

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As said above check for vacuum leaks. Also check for boost leaks. You will need a boost leak tester and a air compressor. Your new stage 2 computer should go to 14.7 psi of boost at wide open throttle.
 

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Discussion Starter #4
Have you checked for vaccuum leaks? How about installing the grainger valve to see if the problem goes away.
I still have the miss at very light throttle and idle is rough but with the grainger installed I can adjust the boost To what ever I want. It pulls nice with the grainger installed at wide open throttle. I am going to check the o2 sensor and if that doesn't work the coil.
 

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R.I.P Dennis Jarvis
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any codes stored?
 

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What plugs does it have and what gap is the electrode set at...how many miles on them, checked them recently for a tiny bit of carbon fouling?

Remove the distributor cap and the HEP device that is under the rotor. Look closely at the HEP cam down inside the distributor housing. It is attached to the distributor shaft and it spins when the engine is running. That cam is simply attached to the shaft with some melted plastic that will loosten over time. If you can hold the shaft and move the cam..even ever so slightly...you need to either JBWeld the plastic cam/shaft 'welds' inside the distributor housing. Clean and dry it real well before application of JB, then let it set at least a full 24 hours before putting in operation....otherwise you need to get a good replacement or rebuilt/new distributor.

Run the car from cold engine to warm up AT NIGHT withthe hood up. Once its started cold, watch the plug wires, cap, and coil for signs of arcing. Let it warm up, and watch it again when it warmed up. Rev it up a number of times as well.

Check your fuel pressure as well, fuel pumps that sit for long periods seem to go weak and fuel filters and fuel clog up when you park them for a while. If the fuel filter hasnt been changed in a while, thats a good service to catch up. Trash in the tank isn't good either but I've not seen one cause a midrange miss UNLESS the fuel injectors were already dirty and partially clogged...that is often accompanied w/a rough idle.

If you are getting atleast 20MPG your O2 sensor is probably doing at least most of its job. When they go South they dont always throw a fault code but your gas mileage will drop to 10MPG or less and thats a good sign it is not doing much work.
 

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Discussion Starter #8
What plugs does it have and what gap is the electrode set at...how many miles on them, checked them recently for a tiny bit of carbon fouling?

Remove the distributor cap and the HEP device that is under the rotor. Look closely at the HEP cam down inside the distributor housing. It is attached to the distributor shaft and it spins when the engine is running. That cam is simply attached to the shaft with some melted plastic that will loosten over time. If you can hold the shaft and move the cam..even ever so slightly...you need to either JBWeld the plastic cam/shaft 'welds' inside the distributor housing. Clean and dry it real well before application of JB, then let it set at least a full 24 hours before putting in operation....otherwise you need to get a good replacement or rebuilt/new distributor.

Run the car from cold engine to warm up AT NIGHT withthe hood up. Once its started cold, watch the plug wires, cap, and coil for signs of arcing. Let it warm up, and watch it again when it warmed up. Rev it up a number of times as well.

Check your fuel pressure as well, fuel pumps that sit for long periods seem to go weak and fuel filters and fuel clog up when you park them for a while. If the fuel filter hasnt been changed in a while, thats a good service to catch up. Trash in the tank isn't good either but I've not seen one cause a midrange miss UNLESS the fuel injectors were already dirty and partially clogged...that is often accompanied w/a rough idle.

If you are getting atleast 20MPG your O2 sensor is probably doing at least most of its job. When they go South they dont always throw a fault code but your gas mileage will drop to 10MPG or less and thats a good sign it is not doing much work.
New plugs wires rotor and cap. I just replace the device under the rotor last summer. Car is getting good fuel mileage 24 mpg and I've been using it hard. I put fuel injection cleaner in the tank yesterday.
I am going to change the fuel filter. I was really thinking it might be the O2 sensor. Now I am at a loss?
 

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What brand plugs and did you check the gap? Also need to confirm no vacuum or boost leaks. Back to the basics, timing, fuel pressure, filters, leaks, codes,,,
 

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Discussion Starter #10
What brand plugs and did you check the gap? Also need to confirm no vacuum or boost leaks. Back to the basics, timing, fuel pressure, filters, leaks, codes,,,
Ac plugs gaped at .035. No leaks. No codes. I have something going on with fuel. It has been getting hot around here. When I park the car for a few minutes it is hard starting. If while it is cranking I hit the throttle pedal it starts right up.
Either a weak pump,clogged filter or bad injectors?
 

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Leaky injector symptom for sure, hard starting when restarted hot after being parked briefly. +1

This can typically be confirmed if you put a fuel pressure guage onthe fuel rail and if when the engine is turned off the fuel pressure will not hold for several moments either there is a leak, or the check valve in the pump is weak or partially clogged or you have a fuel injector leaking raw fuel into the manifold. If the pressure goes down pretty quickly its hard to tell which end the leak is on (fuel pump or injector). I just pinch off the return fuel line real hard and if the pressure continues to decline its got to be leaking at the rail or injector.

An injector that is partially clogged will have a nasty spray pattern that will not atomize well under low or mid vacuum conditions if at all. That could be your not running smooth when cruise but OK under full power.

Many injector sets can be cleaned professionaly for under $100 and they will be just about good as new.

A weak fuel pump onthese cars often exhibit one symptom fairly often, they QUIT when it gets hot outside...especially if the tank is low on fuel. The in-tank pump uses fuel as a cooling system. When you are low on fuel the pumps run hotter. If its (cheap jab) brand new Wagner replacement or a tired old OEM pump, they will start acting up at first, making the car run like crap miss and stumble when it (the pump) gets hot. It might actually quit on you a few times and start right back up in an hour or two once it has cooled off. Been there done that several times. And it seems fairly consistant. If you decide to buy a replacement pump go OEM or go Wallbro..or frankly just sell it and go home...OEMor Wallbro dude on the pumps.
 
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