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I have another post running about my rough idle. I have tried/checked:vacuum leaks, new plugs cap, rotor, cleaned throttle body,AMM, snorkel. Replaced 02 sensor,air filter and other ideas I have learned from search archives.
Now, I have noticed it seems to be idling rough when warm. And, the main fuel pump is very noisy. I have not changed the fuel filter yet, so maybe it is straing to get past a clogged filter. At the same time, the exhaust note, is not one of a smooth idle, but it kind of pops and misses a little and the exhaust pipe shakes with the rough idle, as the fuel pump sings away. Either the pre-pump is not working(I have 12v at the pre-pump) or the main pump is still working, but ready to crap out? It is probably original, 110000 miles. I am going to see if the symptoms are there when it is cold. Thanks for all of the help.
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I filled the tank, and the symptoms don't seem to be as bad. In other words, it still doesn't idle perfect, and I can still hear the fuel pump, but it doesn't seem to be as loud. I have trying various scenarios and it seems to idle and run just fine when cold, but as soon as it warms up, I can hear the fuel pump get a little noisier.
When I pull the #4 fuse (pre-pump) I hear NO difference in the way the car runs. I have searched for countless hours on the board, and the general opinion seems to be that the pre-pumps fail pretty often (old age my guess).
If I unplug the pre-pump fuse, shouldn't I hear some kind of change? It runs exactly the same with the pre-pump fuse in or out. I do have voltage to the pre-pump. Thanks for your help.
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"If I unplug the pre-pump fuse, shouldn't I hear some kind of change? It runs exactly the same with the pre-pump fuse in or out."
At the fuse holder, you can test ("hot wire") the tank pump by itself. Remove fuse 4 and jumper 12V* to the output (right side ) contact. The tank pump should be running.
* Get +12V direct from battery at any fuse 6—10 input (left side) contact.
Jumpering 12V* to fuse 4 input (fuse still out) should run the Main pump.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Lucid,
Thanks for the pre-pump and fuel pump test. I followed your instructions and my pre-pump didn't make a sound. I did the hotwire trick for the main fuel pump as you instructed as well and it runs, runs, runs then buzzes like it is cavatating, then runs again then makes a weird buzzing again and acts like it is starving for fuel or there is air in the line. Is the reason the main pump is so noisy because the pre-pump is not feeding it? Yaaa. I have a full tank of gas now, and have to pull the pre-pump. Fun.
I will now search for hours on the best method of dealing with a full tank and a pre-pump change and how to get that stinkin lock ring off the tank. Any suggestions?
Can I just buy the little pump, and not the whole assembly, and is Walbro the OEM pre-pump?
Where do I go from here? So, this test pretty much says the pre-pump is dead in the water, right? Is there any other reason the pre-pump wouldn't run?
Should I quit driving it until I change the pre-pump?
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Hi Jeff,
I started to write that a full tank is actually less dangerous than an empty one, but I saw Lucid's reply before posting.
Here's what I'll add to Bruce's good advice:
The tank pumps in your vintage were AC. The one FCP ships has no name on it, comes in a ScanTech bag, and so far has been satisfactory in those I've replaced.
Can I just buy the little pump, and not the whole assembly
That depends. A common trouble is not the pump itself, but corrosion at the electrical feed-through connection on the top of the sender assembly. However, even if you determine that's the reason, and the pump itself still works, the reason the tank pumps die is just worn out brushes. So it does sort-of make sense to replace the old pump while you're breathing the fumes anyway.
You'll see in the pics below what the feed-through looks like. And you'll see the style hose (molded and ribbed) used in the '91.
What you'll also see are two problems I've encountered with the replacement sender assemblies - aftermarket, made in Taiwan: The second picture shows one of the pump suppressor choke coils where the insulation was not burned off in soldering, creating an open circuit. The third shows how many of these sender assemblies were mis-wired (not assembled correctly) so as to run the pump backward.
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Art Benstein near Baltimore
By the time a man realizes that his father was right, he has a son who thinks he's wrong.
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Ouch, just priced the OEM pre-pump at my Volvo dealer with my discount. I22.00!! 144.00 list!!
Art,
If you say the FCP scan-tech pump, that is good enough for me. A huge price difference. Plus once you break open the old bung nut, and grease the o-ring, it will probably be easier to access the next time if it were to fail in it's lifetime with me which will probably be it's last hurrah. I plan on driving the wheels off this one 110000 Orig. miles!
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I think I need to retract the "comes in a Scan Tech bag" for faulty memory. I have one yet on the shelf, and the bag is as plain as the pump.
However, if you've read this board at all you'd know the consensus is clear that NOT being in a Scan Tech bag is a good thing. Anyway, I think they used to be bagged by them, certainly not made by them.
The original for 91 was made by AC. I've never seen or heard of a Bosch tank pump, and the VDO tank pumps fit the early 80's.
I used what was handy around the house to turn the bung nut:
--
Art Benstein near Baltimore
The reason a dog has so many friends is that he wags his tail instead of his tongue.
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"I will now search for hours on the best method of dealing with a full tank and a pre-pump change and how to get that stinkin lock ring off the tank. Any suggestions?"
• IMO the full tank won't add any more fumes that a part full one. First clean that whole area as best as you can (brush, scrape, air if you have it). The lock ring can be tapped lose with a length of 1/2" copper pipe having one end flatted and bent at a slight angle. I disconnect the hoses (without going under the car) as follows:
1) The rubber OUTPUT line.
Cut or saw off the rusty hose clamp, use a screwdriver to "assist" the hose off the sender fitting. Refit hose to new fitting. Refasten to sender pipe with new hose clamp.
2) The rubber covered hard plastic RETURN line.
I use a razor knife to slice and cut off about 2" of outer rubber covering to expose black plastic line. Then I cut the plastic line at end of metal sender barb (I use a small, fine-blade hacksaw.)
The cut off plastic end can be reconnected with short piece of 5/16" I.D. fuel hose and 2 good hose clamps. NOTE: Return line is low pressure. IMO, FI rated hose is not needed here, standard Fuel Hose is good enough.
"Can I just buy the little pump, and not the whole assembly, and is Walbro the OEM pre-pump?"
• Check the FCP Groton website. I doubt if Walbro is oem. The job is tough enough to call for long-lived parts. You'll need about 2" of "submersible-rated" hose to reconnect the new pump to the output pipe. FCP may sell it with the pump.
"Where do I go from here? So, this test pretty much says the pre-pump is dead in the water, right? Is there any other reason the pre-pump wouldn't run?"
• You could check for pump voltage at a 2-pin connector in the trunk, feeding the sender/pump. Voltage comes in on Yellow-red wire, goes out on a Brown wire to the pump/sender unit.
"Should I quit driving it until I change the pre-pump?"
• Probably, if possible, to avoid stressing the main pump any further.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Art and Lucid,
Thank you guys very much!! I will follow your advice on this project. I did a pre-pump 15-20 years ago. It is a Florida car and in excellent shape (NO rust, undercarrage in like new condition). I peeked in the access hole and there is no rust at all and it is reasonably clean.
Lucid,
I do have 12v at the yellow/red wire. I believe that Bosch or VDO was OEM. I may get one at the local Volvo dealer where I get a discount. FCP sells an aftermarket that is probably scan tech as Art mentioned. I remember having to double hose clamp that plastic line that you mention. Yeah, I guess it doesn't matter empty or full for this job.
This car was a bargain, but I am getting alittle frustrated at the amount of work I am putting into it. I am in the process of rebuilding the entire front end, and have already done many things to the car.
And finally, could the dead pre-pump be the source of my weird/erratic idle?
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Check out the symptoms when the gas tank is full.
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Art Benstein near Baltimore
Show me a piano falling down a mine shaft, and I'll show you A-flat minor.
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Art,
Thanks for the quick response. Ah yes, the old rotted pre-pump fuel line possibly? I believe this is where you are going with this? Did the 1991's still have rubber hose in the tank, or the plastic line?
It is right at 1/2 tank now, and I had a full tank recently, but didn't notice if symptoms changed with full tank. I will top it off and report back.
I also cleaned checked the idle control, dilectric grease on most connections, checked grounds, sprayed carb cleaner at intake manifold, and injectors, with no change in idle, and so many other things I can't remember them all.
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You mentioned a noisy pump. They are noisy when they are starved of input.
Input being both electricity and fuel.
If you think your fuel is getting there ok, check the electricity. Usual problem is cracked solder on the fuel injection relay. Sorry if you've covered all this in some other thread.
--
Art Benstein near Baltimore
Bakers trade bread recipes on a knead to know basis.
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