Third fuel pump in 6 weeks?!

[mmason]

Anyone have any advice for me. I'd REALLY appreciate it.

I have a 1985 Nissan 720 King Cab with 180,000 miles (almost spot on.) I really like the truck ... when it's driving. I recently bought it from the original owner, and records show it was really well taken care of. Unfortunately, I've had a problem with a no-start.

About 6 weeks ago, the truck died when driving home. I was lucky in that I was able to coast right into my driveway and park it. The truck continued not starting, so I parked it. Eventually a prof. mech friend of mine diagnosed it as needing a replacement fuel pump. We replaced the fuel pump and fuel filter. The truck started and idled for a few minutes, but a couple hours later wouldn't start. We thought that the fuel pump was faulty, and replaced it with another brand (forget which brand now) and again replaced the fuel filter. That seemed to do the trick. I have been driving it nearly daily for the last few weeks. Every now and then, the truck would die as if starved for fuel, but would immediately restart. Then tonight, it died and would not restart, and acted as if the pump wasn't working...which it wasn't.

Has anyone come across anything like this before? Any ideas?

thank
Matt

[bracktheron720]

Dang man sorry about your luck......so far i havnt had any fuel pump problems...but..I remember reading that another guy here had a problem like that...he got it fixed and is now racing his regularly...Id send him a PM if he doesnt come across your post here soon im sure he will though he is on top of things.. His name is "Pezi720" you can find him in just about every thread in the 720 section..

[84_720]

Some electric fuel pump circuits are tied into the engine oil pressure switch (early Chevy Astros for one). I believe this was a safety feature so that in the event of a crash, and the engine died (thus losing oil pressure), the electric fuel pump would stop. Your vehicle may have an intermittent oil pressure circuit wiring problem affecting the fuel pump. Find a circuit schematic for your vehicle to see if this situation applies.

There could also be other intermittent wiring problems in the fuel pump power feed or ground circuits. As much as possible, visually and physically check all wiring connections.

Good luck.

[PEZi]

Some electric fuel pump circuits are tied into the engine oil pressure switch (early Chevy Astros for one). I believe this was a safety feature so that in the event of a crash, and the engine died (thus losing oil pressure), the electric fuel pump would stop. Your vehicle may have an intermittent oil pressure circuit wiring problem affecting the fuel pump. Find a circuit schematic for your vehicle to see if this situation applies.

There could also be other intermittent wiring problems in the fuel pump power feed or ground circuits. As much as possible, visually and physically check all wiring connections.

Good luck.

^ this is extremely possible

my personal problems with the fuel pump were just due to crap pumps basically... i got a good one and it works

one other thing to check... is make sure that your tank isn't deteriorating sending chucks of s*** into lines and whatnot... that obviously might not have anything to do with this... but its good to check

[Charlie69]

Is there a fuel filter between the tank & fuel pump. The original pump should have a built in filter. If you are in deed killing fuel pumps be sure of voltage to the pump, the the pump actually shutting off when the ignition is in the off position. It sounds like the fuel tank might have debri in it causing an intermitant plugging of the fuel line. Use a compressor set at about 20 psi and blow out all the fuel lines in reverse of the flow. Be sure to remove the fuel tank cap and the fuel pump before blowing out the lines. If this solves the problem, then I would say you need to drop the fuel tank and clean it out. Also be sure that all fuel lines are in good shape not loose or cracked and sucking air. The one between the pump and the tank is often neglected. Electric pumps push fuel better than they pull fuel so the closer to the fuel tank the better for installation. Also besure of the pressure of the pump. Fuel injection takes higher pressure pumps than carbureted motors.

[Aven]

This might help.
http://hubpages.com/hub/The-Datsun-and- ... t-Tell-You

[breadbox]

That is an Epic link there Aven. I just saved it to a word file for the vault.

[bracktheron720]

I just remembered that on my truck that the fuel pump is kinda hard wired...theres a little black box type thing that has 3 wires goin in and 3 out im pretty sure..but the wires going in come strait of the distributer its mounted on the charcoal canister box..it pops open and there are 3 connections inside it, the power for my fuel pump comes off one of them..ill snap a pic in a minute to show ya...im not sure why its done like that im guessing its to bypass all the relays and junk...thats how i got it...pump comes one with the key in the run position....

[bracktheron720]

Heres the box....you can see the extra wire coming off the top connection its the one with the blue crimp connector it runs to an inline fuse and back to the fuel pump..maybe give this a try and see what happens....

[mmason]

Thank you everyone. Those are some good ideas, and I need to get the truck home and take a closer look. Right now, it's parked at a grocery store parking lot.

Many thanks
Matt

[Ozzy]

Im not gonna tell you your fuel pump is operational, thats easy enough to check, but what startled me about your post is the striking similiarity to a problem I am still fixing on my '82 720 4X4. Same symptoms. So of course you change the fuel filter, pump, check pressure, blow out lines, check carb float and float valve. Then you start scratching your head and say well if it aint fuel, it must be electrical. So you change the plugs, cap & rotor, check timing, wires.......and the problem persists. Always starts, idles well, might even go for a while. Then it dies again and you know you havn't solved the problem. You'll think back about the fuel again, what did I miss. Then you think back to electrical, probe deeper into the dizzy. There, depending on the modle year, you might find an ignition control module. These little bastards will humble you, and they are known to die on these Datsuns. The problems they create are very difficult for average home mechanics to diagnose because when they fail its often intermittent, and if you're a greenhorn you will have a very healthy fuel system and complete tune-up by the time you figure this out, which isnt a bad thing, but can empty the pocketbook. Following the 'don't throw parts at a car, diagnose the problem' philosophy I only invested in a cap and rotor and mine looked sooo bad (read: TOAST!) I didn't feel the least bit of regret. But it didn't make the truck run any better. I suspected the I.C. module and with a bit of interweb research learned that this is a weak point of the ignition system in many of these Datsuns. The '82 is a 2 sparkplug per cylinder system and I learned from someone with an SX that because the sparks are simultanious (exaust and intake fire at the same time on each cylinder) you can switch the coil leads, thus reversing the intake and exaust signal from the I.C. unit. The reason for this test is because the truck is said to be able to idle well on the exaust plugs but it wont run well under a load on them. That's why it always starts, even if it stalls 3 seconds later, or 1/8 mile up the drive way. In my case swapping leads didn't help, either because the whole I.C. unit is fried, or because it's not the I.C. unit causing the problem. But I'm way down the road (don't know how long the road is!!!) on this diagnosis and was ready to 'throw' a part at it, literally, because this issue has just about driven me to the loony bin. Problem is, when you first look up the i.c. module you get prices from 272.00 to 456.00 bucks. No s***'!! I quickly found out that a whole new dizzy including I.C. mod. is 136.00. I think you need an occiliscope to test the I.C. module, not totally sure, but I don't have one handy. Then a Datsun friend came up with a I.C. module NOS and it's on the way in the mail.
Let's face it, parts new from the store are faulty a surprisingly high percentage of the time, but 3 pumps, all bad.....and the same symptoms, I'd look toward that I.C. module, if you have one on the '85. If not, as a test, run direct power from the battery to the pump to eliminate any other wiring issue(electric pump). If it's just a bad pump, be glad, although they can be expensive. Check the fuel pressure. If carburated check the sight glass to be sure fuel is at the proper level (stock carb). If you find your self scratching ye olde head cause theres tons of fuel and adequate pressure, look to the electrical.
I was imagining a test like this: If it's running rough or keeps stalling use a bit of starting fluid or propane (If you know how to do it safely) to see if the idle comes up, which would indicate a fuel issue. If the test is run correctly you should be able to determine that it is indeed a starvation of fuel. Think of the test like putting a few drops of gas in the carb to get an 'out of gas' or 'sat too long' engine to run. If it doesn't make a difference(engine doesn't rev up) then it's probably not a fuel issue at all. Look to spark!!!
I'll post my own findings with regard to the I.C. module as soon as it shows up and I put it in which will probably be Tuesday May 18th, 2010. Till then I have to be satisfied with today's minor triumph, fixing the ignition start switch (30-40 bucks new) with 50 cents worth of super glue and epoxy!!! Good luck!!!

[nlaforge13]

On mine the wiring to the ignition was crap so I ended up wiring it dirrectly to the battery with a flip switch so now I know for sure if its on or not

[flinterman2000]

Well Ozzy I'm sorry to disappoint you, but they do not fire together. It's an emission thing. They fire about 13 degrees apart, this allows the flame front to burn first giving power and the second spark ensures all fuel is completely burned in the cylinder. The 8 plug CA engine fires together though and thats a performance thing, more spark causes faster burn of the atomized fuel resulting in more power but it is not as environmentally friendly as the Z engine. On the Z20 I had I got rid of the electronic dizzy and installed a points dizzy and that solved the problem.

[Ozzy]

Thanks for the correction. ok, would 13 degrees in difference sustain smooth idle? Mine maintained a smooth idle, but stalled under a load. It's also possible that a failing i.c. module could produce an adequate spark at idle speed but have a more pronounced problem under the demand of acceleration and load. My understanding is that like a failing coil (although the i.c. is a transistor, pretty sure) they tend to fail as they heat up, hence,tend to always start cold and idle for at least a little while. Mine would do this but then when you went to take it for a drive it would only go 1/8 mile, stall, re-start, stall......till you let it cool off an hour or so. Then it would repeat the process. Or occasionally run for 6 miles. Very frustrating to diagnose. Im still waiting for the i.c. module in the mail. In any event the i.c module is a know weak point. I get this information from posts on the net but also directly from a professional mechanic who said that the symptoms I described perfectly matched this know problem. So all in all, if others run into an intermittant stalling or loss of power, and everything else checks out (fuel system, and most of the obvious ignition parts, they may want to consider the i.c. module as a potential culprit. I'll post when I get the i.c. installed.

[Aven]

I had the same problem with mine. Idle fine and immediately die under load. Turned out to be a vac line issue. I had two reversed.

[flinterman2000]

mmason and Ozzy, you guys need to really check the vac system first. I mean thoroughly check it first. Yes Ozzy, the emission system is set up to operate smoothly though out the rpm range and depending on how bad the IC is it will cause these symptoms. Under load there is a lot more current passing through the IC raising the heat levels, breaking it down more. This is when it starts stuttering or fails completely.

[Ron in Radio Heaven]

I have an '85 Kingcab and had the exact same problem.
The garage worked on it on and off for a year, it was very intermittent.
They finally started replacing the fuel pump.
After the third one from NAPA, AutoZone, etc.
I finally suggested they get one from the Nissan dealership.
That was a year and a half ago and the truck has run fine ever
since.
The junk they sell at the retail parts houses that's made in China
just won't work. From what I understand now is that these pumps
have an internal ground that doesn't work with this truck.

The fuel pump from the dealer is expensive, over $200, but IT WORKS ! ! !
It hasn't died on me once since it was installed.

73, Ron w4ron

[Ozzy]

mmason and Ozzy, you guys need to really check the vac system first. I mean thoroughly check it first. Yes Ozzy, the emission system is set up to operate smoothly though out the rpm range and depending on how bad the IC is it will cause these symptoms. Under load there is a lot more current passing through the IC raising the heat levels, breaking it down more. This is when it starts stuttering or fails completely.

Will Check the vac system more thuroughly. I did do a preliminary check on it. What led me away from this, and a fuel issue, is that sometimes the truck drives quite a distance with out sputtering or stalling. A failing vac line could do this I suppose, if it's just starting to crack or whatever, and I will double check those lines. As for fuel I drove this truck 10,000 miles with the existing fuel pump. Pressure checks out within spec. at the carb and flow is adequate. Blew out the lines. Bypassed the lines. Changed the pump......same symptoms. I had to move on to other potential issues at that point. i.e. electrical.
I get the new i.c unit today. Will post results soon. Thanks everyone.

[offroadbob]

I had the same problem about 10 years back, I ended up just running a piggyback line from the fuse box to the fuel pump. It did the trick! i know it would have been better to run a relay and the like but... its been working for 10 years now so. good luck!!