97 12 valve hard start
10-14-2018, 10:28 AM
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97 12 valve hard start
I recently bought a 1997 12 valve 3500 5 speed truck that won't start without a small shot of ether. Doesn't matter if the engine is hot or cold, or if it's been sitting or not. I primed it with the lift pump, and to me it sounds like it primes up, but still won't start on it's own. Even after it does start with ether, it won't start back at all on it's own after I shut it down. After it starts it seems to run great, and sounds good. The return line doesn't seem to be leaking, so I'm wondering what the problem could be. Could the grid heater cause this? Or should I replace the overflow valve first? It just takes a small shot of ether to start it, but it just cranks and cranks without it. The engine is factory stock as far as I can tell. Any suggestions are appreciated.................
Barry
Barry
10-14-2018, 07:14 PM
#2
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Are you giving it part throttle like Dodge recommends when starting it?
Or just turning the key?
I have owned many P-pumped 12Vs that will not start without partial throttle pedal input.
I would not use ether to start my own truck, unless it was a last call.........
Or just turning the key?
I have owned many P-pumped 12Vs that will not start without partial throttle pedal input.
I would not use ether to start my own truck, unless it was a last call.........
10-15-2018, 03:20 PM
#3
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The grid heater shouldn't cause your symptoms, unless you were perhaps in very cold temps.
When you prime with the lift pump, do you eventually hear a whistling/squeaking sound from the front of the injection pump? If so, that is the sound of the OFV (overflow valve) bypassing and it's the sign that you've primed up to the OFV. Does it take a lot of strokes of the priming button to do that?
I'm guessing you don't have a fuel pressure gauge on it - I'd run a fuel pressure gauge from the outlet banjo bolt of the filter housing or inlet banjo bolt to the IP (search the forums for threads on that topic). That will let you do some testing on both the OFV and lift pump.
What's your idle speed set at? According to AllData, factory spec for a '96 with manual trans is 750 RPM with AC on.
You may have an air leak somewhere on the suction side of the lift pump. I saw a thread where something rubbed on the line inside the tank and wore a hold through it - below a certain fuel level, the owner had an air leak that made starting impossible (or at least very difficult)
When you prime with the lift pump, do you eventually hear a whistling/squeaking sound from the front of the injection pump? If so, that is the sound of the OFV (overflow valve) bypassing and it's the sign that you've primed up to the OFV. Does it take a lot of strokes of the priming button to do that?
I'm guessing you don't have a fuel pressure gauge on it - I'd run a fuel pressure gauge from the outlet banjo bolt of the filter housing or inlet banjo bolt to the IP (search the forums for threads on that topic). That will let you do some testing on both the OFV and lift pump.
What's your idle speed set at? According to AllData, factory spec for a '96 with manual trans is 750 RPM with AC on.
You may have an air leak somewhere on the suction side of the lift pump. I saw a thread where something rubbed on the line inside the tank and wore a hold through it - below a certain fuel level, the owner had an air leak that made starting impossible (or at least very difficult)
10-15-2018, 04:25 PM
#4
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The grid heater shouldn't cause your symptoms, unless you were perhaps in very cold temps.
When you prime with the lift pump, do you eventually hear a whistling/squeaking sound from the front of the injection pump? If so, that is the sound of the OFV (overflow valve) bypassing and it's the sign that you've primed up to the OFV. Does it take a lot of strokes of the priming button to do that?
I'm guessing you don't have a fuel pressure gauge on it - I'd run a fuel pressure gauge from the outlet banjo bolt of the filter housing or inlet banjo bolt to the IP (search the forums for threads on that topic). That will let you do some testing on both the OFV and lift pump.
What's your idle speed set at? According to AllData, factory spec for a '96 with manual trans is 750 RPM with AC on.
You may have an air leak somewhere on the suction side of the lift pump. I saw a thread where something rubbed on the line inside the tank and wore a hold through it - below a certain fuel level, the owner had an air leak that made starting impossible (or at least very difficult)
When you prime with the lift pump, do you eventually hear a whistling/squeaking sound from the front of the injection pump? If so, that is the sound of the OFV (overflow valve) bypassing and it's the sign that you've primed up to the OFV. Does it take a lot of strokes of the priming button to do that?
I'm guessing you don't have a fuel pressure gauge on it - I'd run a fuel pressure gauge from the outlet banjo bolt of the filter housing or inlet banjo bolt to the IP (search the forums for threads on that topic). That will let you do some testing on both the OFV and lift pump.
What's your idle speed set at? According to AllData, factory spec for a '96 with manual trans is 750 RPM with AC on.
You may have an air leak somewhere on the suction side of the lift pump. I saw a thread where something rubbed on the line inside the tank and wore a hold through it - below a certain fuel level, the owner had an air leak that made starting impossible (or at least very difficult)
10-16-2018, 06:07 PM
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The grid heater shouldn't cause your symptoms, unless you were perhaps in very cold temps.
When you prime with the lift pump, do you eventually hear a whistling/squeaking sound from the front of the injection pump? If so, that is the sound of the OFV (overflow valve) bypassing and it's the sign that you've primed up to the OFV. Does it take a lot of strokes of the priming button to do that?
I'm guessing you don't have a fuel pressure gauge on it - I'd run a fuel pressure gauge from the outlet banjo bolt of the filter housing or inlet banjo bolt to the IP (search the forums for threads on that topic). That will let you do some testing on both the OFV and lift pump.
What's your idle speed set at? According to AllData, factory spec for a '96 with manual trans is 750 RPM with AC on.
You may have an air leak somewhere on the suction side of the lift pump. I saw a thread where something rubbed on the line inside the tank and wore a hold through it - below a certain fuel level, the owner had an air leak that made starting impossible (or at least very difficult)
When you prime with the lift pump, do you eventually hear a whistling/squeaking sound from the front of the injection pump? If so, that is the sound of the OFV (overflow valve) bypassing and it's the sign that you've primed up to the OFV. Does it take a lot of strokes of the priming button to do that?
I'm guessing you don't have a fuel pressure gauge on it - I'd run a fuel pressure gauge from the outlet banjo bolt of the filter housing or inlet banjo bolt to the IP (search the forums for threads on that topic). That will let you do some testing on both the OFV and lift pump.
What's your idle speed set at? According to AllData, factory spec for a '96 with manual trans is 750 RPM with AC on.
You may have an air leak somewhere on the suction side of the lift pump. I saw a thread where something rubbed on the line inside the tank and wore a hold through it - below a certain fuel level, the owner had an air leak that made starting impossible (or at least very difficult)
10-16-2018, 06:10 PM
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Are you giving it part throttle like Dodge recommends when starting it?
Or just turning the key?
I have owned many P-pumped 12Vs that will not start without partial throttle pedal input.
I would not use ether to start my own truck, unless it was a last call.........
Or just turning the key?
I have owned many P-pumped 12Vs that will not start without partial throttle pedal input.
I would not use ether to start my own truck, unless it was a last call.........
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10-17-2018, 09:18 AM
#8
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It is a bit of a long shot, but have you checked that the FSS is lifting the arm up all the way?
If it is not it might be limiting the fuel flow and making it harder to start....
Try turning the key on till just before it cranks and lift the FSS lever up by hand, then turn the motor over.
If it is not it might be limiting the fuel flow and making it harder to start....
Try turning the key on till just before it cranks and lift the FSS lever up by hand, then turn the motor over.
10-17-2018, 01:23 PM
#9
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In that line, perhaps the FSS is improperly adjusted - though I would think you'd notice that at higher engine speeds. Try what Oliver suggested, to verify the FSS is lifting as far as it can as it is currently adjusted - then check the adjustment by disconnecting the FSS completely and see if the arm can go up even farther.
As to the earlier question of idle speed - the tach is not accurate enough for setting idle speed and the factory service manual makes a point of that (you should set idle speed with a scan tool, optical tach. or mulimeter with frequency measurement). I find my tach to be off by about 40 RPM, but its close enough to tell me if my idle speed is in the ballpark.
As to the earlier question of idle speed - the tach is not accurate enough for setting idle speed and the factory service manual makes a point of that (you should set idle speed with a scan tool, optical tach. or mulimeter with frequency measurement). I find my tach to be off by about 40 RPM, but its close enough to tell me if my idle speed is in the ballpark.
10-26-2018, 07:34 AM
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Well, I took the FSS off, although it seemed to be working fine. I cracked lines at no.'s 2, 3, and no. 4 injectors and I pumped the primer button for an extremely long time. No's 2 and 3 finally looked a little bit wet, no. 4 never showed anything. Truck still won't start on it's own. How much fuel should I see at the injector lines? I can crack the fitting on top of the filter housing, and I get plenty of fuel there. I also get the air sound at the overflow valve after 4 or 5 strokes. Does that mean the overflow valve is ok? What's weird about all this is I can get the truck started with a shot of ether, and it runs and sounds great after it starts. This one has really got me.....................................
Barry
Barry
10-26-2018, 09:03 AM
#12
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Pumping the primer button with the fuel arm in the closed position shouldn't give you anything at the injector lines. The way to test for fuel delivery to the injectors is to have the fuel arm all the way open (with the FSS or wired open), crack the lines at the injectors, and crank it a few seconds. You should see fuel squirting out. If you can do this right after you've shut the truck off. you should see fuel squirting very quickly. When I was repriming my injector lines, I could see the fuel squirt from inside the truck by looking through the gap between hood and cowl with the hood up.
The OFV sound doesn't mean its good or bad - just that you are getting fuel to that point and it's now going through the OFV and the return line to the tank. Whatever pressure will lift the ball in the OFV off its seat is whatever pressure it is - whether the OFV is good or bad. It's possible the OFV is bad, but you need a fuel pressure gauge plumbed in between the lift pump and the inlet to the P7100 pump to test it - then with the engine running, you could pinch shut the rubber return line to the tank and see how the pressure responds. you can do this at idle, but the effect is more pronounced at higher speed. According to factory info, you're looking for 17-22 PSI at idle, 25-35 PSI at 2500 RPM (no load). Pressure increase means bad OFV, no increase means bad lift pump (and possibly bad OFV - retest after replacing lift pump).
By the way, how long has it been since you replaced the fuel filter?
The OFV sound doesn't mean its good or bad - just that you are getting fuel to that point and it's now going through the OFV and the return line to the tank. Whatever pressure will lift the ball in the OFV off its seat is whatever pressure it is - whether the OFV is good or bad. It's possible the OFV is bad, but you need a fuel pressure gauge plumbed in between the lift pump and the inlet to the P7100 pump to test it - then with the engine running, you could pinch shut the rubber return line to the tank and see how the pressure responds. you can do this at idle, but the effect is more pronounced at higher speed. According to factory info, you're looking for 17-22 PSI at idle, 25-35 PSI at 2500 RPM (no load). Pressure increase means bad OFV, no increase means bad lift pump (and possibly bad OFV - retest after replacing lift pump).
By the way, how long has it been since you replaced the fuel filter?
10-26-2018, 05:18 PM
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Pumping the primer button with the fuel arm in the closed position shouldn't give you anything at the injector lines. The way to test for fuel delivery to the injectors is to have the fuel arm all the way open (with the FSS or wired open), crack the lines at the injectors, and crank it a few seconds. You should see fuel squirting out. If you can do this right after you've shut the truck off. you should see fuel squirting very quickly. When I was repriming my injector lines, I could see the fuel squirt from inside the truck by looking through the gap between hood and cowl with the hood up.
The OFV sound doesn't mean its good or bad - just that you are getting fuel to that point and it's now going through the OFV and the return line to the tank. Whatever pressure will lift the ball in the OFV off its seat is whatever pressure it is - whether the OFV is good or bad. It's possible the OFV is bad, but you need a fuel pressure gauge plumbed in between the lift pump and the inlet to the P7100 pump to test it - then with the engine running, you could pinch shut the rubber return line to the tank and see how the pressure responds. you can do this at idle, but the effect is more pronounced at higher speed. According to factory info, you're looking for 17-22 PSI at idle, 25-35 PSI at 2500 RPM (no load). Pressure increase means bad OFV, no increase means bad lift pump (and possibly bad OFV - retest after replacing lift pump).
By the way, how long has it been since you replaced the fuel filter?
The OFV sound doesn't mean its good or bad - just that you are getting fuel to that point and it's now going through the OFV and the return line to the tank. Whatever pressure will lift the ball in the OFV off its seat is whatever pressure it is - whether the OFV is good or bad. It's possible the OFV is bad, but you need a fuel pressure gauge plumbed in between the lift pump and the inlet to the P7100 pump to test it - then with the engine running, you could pinch shut the rubber return line to the tank and see how the pressure responds. you can do this at idle, but the effect is more pronounced at higher speed. According to factory info, you're looking for 17-22 PSI at idle, 25-35 PSI at 2500 RPM (no load). Pressure increase means bad OFV, no increase means bad lift pump (and possibly bad OFV - retest after replacing lift pump).
By the way, how long has it been since you replaced the fuel filter?
10-26-2018, 08:06 PM
#14
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Please change the filter. 
You can bleed through a clogged filter and relieve the overflow quite easily with the truck off, running may be a different scenario.
Then check fuel pressure. Easiest way is to replace the bleeder screw on top of filter housing, or drill and tap the banjo bolt feeding the injector pump with 1/8" npt and thread in a needle valve. Feed out with some 1/8 or 1/4 inch line to a cheap 60psi gauge.
Could be a governor problem I guess, or sticky fuel rack, although not common.
You can bleed through a clogged filter and relieve the overflow quite easily with the truck off, running may be a different scenario. Then check fuel pressure. Easiest way is to replace the bleeder screw on top of filter housing, or drill and tap the banjo bolt feeding the injector pump with 1/8" npt and thread in a needle valve. Feed out with some 1/8 or 1/4 inch line to a cheap 60psi gauge.
Could be a governor problem I guess, or sticky fuel rack, although not common.
