Anyone know why the timing would change? Is that just wear & tear on the timing parts?
Emergency - Can a mechanical fuel pump fail intermittently?
Hey guys,
My '87 3.9L Dakota just quit on me and I've got to get it fixed TODAY. I think it's the fuel pump, but let me know if you think it's something else.
Going down the road the engine just died - no sputtering or anything. BUT when I pumped the gas it ran briefly, less than a second. That was while I was still coasting in Drive. It did that the first 2 or 3 times I pumped the gas, but not again.
After sitting about 45 minutes, it started after cranking for a couple of seconds.
I think the carb is being starved of fuel, the brief seconds it ran were when the accelerator pump shot fuel from the bowl (assuming this carb has a bowl), but then ran the bowl dry. I think that's also why, when it did start again, it took a few seconds of cranking.
But I don't understand why it would start again after sitting a few minutes. That's what makes me unsure if its the fuel pump or not.
The fuel filter was replaced in August.
If I was flush with cash I'd just slap a new pump and filter on it. Right now I've got be careful what I spend the $$ on.
I thought about water in the gas, but wouldn't that make it sputter for a while before it just quit completely?
My '87 3.9L Dakota just quit on me and I've got to get it fixed TODAY. I think it's the fuel pump, but let me know if you think it's something else.
Going down the road the engine just died - no sputtering or anything. BUT when I pumped the gas it ran briefly, less than a second. That was while I was still coasting in Drive. It did that the first 2 or 3 times I pumped the gas, but not again.
After sitting about 45 minutes, it started after cranking for a couple of seconds.
I think the carb is being starved of fuel, the brief seconds it ran were when the accelerator pump shot fuel from the bowl (assuming this carb has a bowl), but then ran the bowl dry. I think that's also why, when it did start again, it took a few seconds of cranking.
But I don't understand why it would start again after sitting a few minutes. That's what makes me unsure if its the fuel pump or not.
The fuel filter was replaced in August.
If I was flush with cash I'd just slap a new pump and filter on it. Right now I've got be careful what I spend the $$ on.
I thought about water in the gas, but wouldn't that make it sputter for a while before it just quit completely?
101 - 120 of 120 Posts
No, someone probably messed with it once.
Well, I was the last person to mess with it. I set it to the same place using the same procedure about 4 years ago.
After setting the timing to roughly 7 degrees BTDC, I drove 14 miles each way on the highway yesterday. No problem on the early drive, but had some trouble toward the end of the noon drive back, mainly when increasing the throttle to go up a hill. Mileage is also terrible - 3/4 of a tank just to go 145 miles. That's about 10mpg. I usually get 15-16. Trying to find the time to check the plugs. Still need an O2 sensor, but any new parts will have to wait 3 weeks.
Someone mentioned the ignition pickup as a possible problem when the engine was quitting. Would this stuttering be consistent w/ a bad pickup or do they just fail completely?
Someone mentioned the ignition pickup as a possible problem when the engine was quitting. Would this stuttering be consistent w/ a bad pickup or do they just fail completely?
Either one.
A bad O2 sensor can cut your mileage in half, if it's really bad.
A bad O2 sensor can cut your mileage in half, if it's really bad.
Coupla questions on the O2 sensor and timing.Bob Lincoln said:Either one.
A bad O2 sensor can cut your mileage in half, if it's really bad.
What's the effect of a cracked exhaust manifold on the sensor? It's cracked all the way around just forward of the center attach points.
Would a failed sensor make the computer think the engine is running rich? What does the computer do by default w/out info from the sensor?
Would the computer try to manage a rich mixture by advancing the timing?
A cracked exhaust manifold, of course, is a serious CO poisoning hazard, that's the worst result. But also, since it's leaking exhaust upstream of the O2 sensor, the sensor's reading will be affected, not sure if it would read richer or leaner. With less exhaust backpressure in the manifold, the sensor won't read as high an HC content, I imagine, so it might read lean. Reading lean can prompt the computer to richen the mixture.
A sensor can fail rich or lean. If the signal is within range, the ECM will adjust the mixture a little richer or leaner. If the sensor is out of range, the ECM will go into open loop programming, which means it will use a default air/fuel mixture table that won't be optimized for all driving conditions. As a default, they tend to make it run richer, so as not to lean out under any conditions, which could burn a piston and cause other damage. I don't believe it would affect the timing. Advancing the timing farther than normal usually causes higher HC emissions, as it sparks too early and the flame front largely passes before all the fuel is mixed and compressed.
A sensor can fail rich or lean. If the signal is within range, the ECM will adjust the mixture a little richer or leaner. If the sensor is out of range, the ECM will go into open loop programming, which means it will use a default air/fuel mixture table that won't be optimized for all driving conditions. As a default, they tend to make it run richer, so as not to lean out under any conditions, which could burn a piston and cause other damage. I don't believe it would affect the timing. Advancing the timing farther than normal usually causes higher HC emissions, as it sparks too early and the flame front largely passes before all the fuel is mixed and compressed.
On the carbureted V6, how does the ECM control mixture? I thought the only thing it could adjust was the timing.
Sorry, again, I'm a victim of my own mindset. Duh. No EFI in your truck. I'm 28 years away from carburetors.
So, no active mixture control, I guess. Perhaps it changes the timing, and I'll guess that it would retard it slightly.
So, no active mixture control, I guess. Perhaps it changes the timing, and I'll guess that it would retard it slightly.
The carb has electronic controls on it - ie: a feedback carb and the O2 sensor can adjust the air/duel mixture. I'm sure it can't adjust in as wide a range as fuel injection but the carb can adjust somewhat.On the carbureted V6, how does the ECM control mixture? I thought the only thing it could adjust was the timing.
I think I just figured out the source of the stuttering problem! I was able to buy a distributor cap and plugs today. The old plugs were in very bad shape. All except one were over-gapped, some electrodes were worn down at an angle, and one had a ground that was covered in crud. I assume all the fouling combined w/ being too far advanced caused this.
Haven't driven on the highway, but I'm guessing this is the source of the problem and probably part of the lousy mpg. Still need to get an O2 sensor - probably later this month.
Haven't driven on the highway, but I'm guessing this is the source of the problem and probably part of the lousy mpg. Still need to get an O2 sensor - probably later this month.
How many miles were on the plugs? I thought you had replaced them.
No, I didn't have the $$ till today. Looks like they had 31k miles on them. I'll try to post a pic of them tomorrow.Bob Lincoln said:How many miles were on the plugs? I thought you had replaced them.
I borrowed a multimeter to test the O2 sensor. I need some help interpreting the readings, though.
W/ the engine warm from a 10 mile highway drive, but having sat for about 15 minutes, on the 2000m VDC scale it registered about 310 at idle. When I revved up the engine, it dropped to 190 then came back up pretty quickly. As the engine warmed back up, the reading rose. Before I finished it was up to about 440 at idle and dropped to 290 when revved.
On the 200m VDC scale at idle all I got was a 1, a couple of spaces, and a decimal point. When I revved the engine I would get 168.9, 153.6, 186.5, 182.9, and 160.8 for a split second on each rev.
So obviously the O2 sensor is registering something. My take on this is that replacing the O2 sensor is not an emergency, but still needs to be done soon just because of how old it is. Let me know what you guys think.
BTW, no stuttering on the highway drive, but there's not too many hills on that trip. The Sunday drive to church will be the test.
W/ the engine warm from a 10 mile highway drive, but having sat for about 15 minutes, on the 2000m VDC scale it registered about 310 at idle. When I revved up the engine, it dropped to 190 then came back up pretty quickly. As the engine warmed back up, the reading rose. Before I finished it was up to about 440 at idle and dropped to 290 when revved.
On the 200m VDC scale at idle all I got was a 1, a couple of spaces, and a decimal point. When I revved the engine I would get 168.9, 153.6, 186.5, 182.9, and 160.8 for a split second on each rev.
So obviously the O2 sensor is registering something. My take on this is that replacing the O2 sensor is not an emergency, but still needs to be done soon just because of how old it is. Let me know what you guys think.
BTW, no stuttering on the highway drive, but there's not too many hills on that trip. The Sunday drive to church will be the test.
I'd run a tankful and get an mpg reading before replacing anything else. The plugs could have been entirely responsible for the poor mileage. The O2 sensor in my 84 Daytona is original at 131K miles, and I've had some last 190K miles with no problem.
A multimeter really can't test an O2 sensor properly. The readings change too fast for the meter to update and display them, so you're seeing an average, not a meaningful reading. You really need a scope for testing. If mileage is still way off, replace. If it goes back to normal, it's fine. My Dakota gets 19-20 mpg highway, and a standard cab 2WD should get 22-25. I get about 16 mpg city.
A multimeter really can't test an O2 sensor properly. The readings change too fast for the meter to update and display them, so you're seeing an average, not a meaningful reading. You really need a scope for testing. If mileage is still way off, replace. If it goes back to normal, it's fine. My Dakota gets 19-20 mpg highway, and a standard cab 2WD should get 22-25. I get about 16 mpg city.
31K is awful soon for plugs to look that bad, but it could be a combination of it being out of tune and the "wrong" plugs in it. I've had Bosch Platinum plugs look like crap after 10k miles but most others have lasted far longer.No, I didn't have the $$ till today. Looks like they had 31k miles on them. I'll try to post a pic of them tomorrow.
A bad rotor can do this, and cap. I don't remember, what was the story on those?
I replaced the cap and rotor, but I didn't think they looked that bad. There was some material built up on the contacts in the cap, but it wiped right off. I replaced the rotor a couple weeks ago and didn't notice any improvement. I replaced the cap yesterday along w/ the plugs.
It's vital on this engine and the 318 to use a cap that has brass inserts and not aluminum. That white residue is aluminum oxide and forms quickly, and causes misfires and reduced spark.
I did not know that. I'll swap out the cap as soon as possible. Thanks Bob.Bob Lincoln said:It's vital on this engine and the 318 to use a cap that has brass inserts and not aluminum. That white residue is aluminum oxide and forms quickly, and causes misfires and reduced spark.
Looks like the new spark plugs took care of the stuttering problem. Didn't have a single hiccup on the drive to and from church. Good to feel like I can trust my truck again.
Next project is getting the linkage fixed between the ignition key and the ignition switch (one of my other topics).
Thanks again to everyone for all the help! This one has really been a learning experience!
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