argh.. figures..

i was just about to dump some $ on something i want (nice new shiney exhaust) and now i have the funny feeling it's all going to go to more factory replacement parts.. :(

anyone know how to get the codes outta the computer..i remember seeing it somewhere.. something about a paper clip.. but can't dig it up via the search for some reason..

Here's the problem anyway..

truck started to be hard to start and had a slight miss at times.. sooo.. decided to do some maintance.. new fuel filter, new air filter.. drained the fuel bowl (lotsa crap came out) and an oil change..

it was much happier.. for about 2-3 hours.. now it bucks and misses, it doesn't want to start (have to crank till the oil pressure comes up then it will start)..

and for some reason i can't bleed enough air out.. i open the valve.. air comes out.. get it to have a nice no air stream of fuel coming out of it.. and then.. close it.. go back an hour later.. more air..

i'm wondering if the fuel filter isn't seated properly and is suckin air in somehow.. either that or the lift pump is shot.. because.. isn't it supposed to pump when you initially turn the key from off to run to prime the pump till the oil pressure comes up?

now i also remember seeing that the fuel inlet ? on the pump has a stainless screen on it as well.. where abouts is that so i can check it? it's entirly possible it's full of crap as there was tons of crap in the fuel bowl when i cleaned it out. perhaps some got by the filter and it's starving the engine for fuel?

-- WheatKing

pull your fuel filter back off and make sure that no parts of the old seal are still there. it happened to me.

Air in the fuel filter housing would mean a bad seal or leak in the fuel line comming in. Don't forget that you can get the pump to prime the fuel bowl with the truck in gear, turn the key to start, truck won't start but lift pump should rattle away.


Checking for codes is a paperclip in the ALDL port between pins A and B on a pre OBDOII. It located under the dash below the steering wheel. When your done hold the APP all the down for a second and it will clear everything but code 12 engine off.

the APP? lost me there..

so pins A+B and the check engine should flash right?

and the trunk in gear to prime. i was missing the in gear part :)

I'll give this a shot on my lunch.. nothing like walkin around the office smelling like Diesel :)

The APP is the fuel pedal position sensor.


Jump pin a to b and turn key to on position, get codes, then step on APP for a two sec count and all should clear.


Air leak is probably filter lid not on right, if o-ring and metal ring are out of position it won't go on right, seen that once. Without adaquate pressure, truck will hard start and run like crap.

If it is a bad seal after the lift pump, shouldn't it be leaking fuel?


My '93 was doing something kind of similar recently. It turned out to be a kinked fuel line just before the filter. It had a lot of vacuum in it when I would open the bleeder.

Got dieselly reside in the valley of the engine where the fuel filter goes?

Did you try opening the water drain when it is running bad? If you have a good flow out of it but no fuel out of the filter bleeder then it is a plugged filter. (bad fuel could have plugged it that fast)

Took the filter out... made sure the seal was ok.. the bowl was empty.. maybe 1/2" of fuel in the bottom..

i get fuel out the breather.. but once i get it all bled.. and take it for a drive.. i get air back in again..

i dunno whats wrong.. i'm gonna pop the old filter back in see if the new one is infact plugged somehow..

TDG.. maybe i'll limp it down to your shop as soon as those pipes come in.. i need to get this running right..

How are you priming it? It is probably easiest to unplug the wire off the oil pressure sensor and put a jumper wire between the two outside pins. Then just let it run continous and start wiggling the rubber hoses aroung the filter. If if has a kink, you will hear the pump get loud when it opens a little.


If that doesn't work, you might have a plugged pickup in the tank.


Do you have an air compresser? If so, take the line from the tank off the lift pump and blow air down it. (you need to remove the fuel cap)

i have a compressor..

i doubt iwant to be blasting 90psi of air down the line however.. haha..

where about is the oil pressure sender.. the only way i've been able to get it to start to prime is by crankin it.. (can't start it in gear.. ignition interlock.. maybe quantum has a busted ignition switch? haha)

and where abouts is the lift pump.. is it in the tank or in the engine compartment?

me thinks i'm gonna have to get a manual for this beast.

-- WheatKing

The fuel pump is on the frame rail under the truck. If you go straight under from the center of the driver door you will see it. It looks like the filter on a GM gas vehicle.


If reach down next to the fuel filter (slightly to the driverside and back) you should feel the OPS. It isn't that hard to unplug it and plug it back in.


I just used a blow nossle on the compressor hose on my 93. If you don't take the fuel cap off, it will pressureise the tank then blast fuel back out the fuel line.

i'll give it a shot.. Thanks for the info :)

i have a compressor..

i doubt iwant to be blasting 90psi of air down the line however.. haha..

where about is the oil pressure sender.. the only way i've been able to get it to start to prime is by crankin it.. (can't start it in gear.. ignition interlock.. maybe quantum has a busted ignition switch? haha)

and where abouts is the lift pump.. is it in the tank or in the engine compartment?

me thinks i'm gonna have to get a manual for this beast.

-- WheatKing


I think you missed what QM was saying about priming.


put the truck in gear like Drive on an Auto or 1st gear with a manual and clutch out. Turn the key to crank the starter WILL NOT engage but you will send power to the lift pump to prime the fuel filter and IP. I hope this helps clear it up. I wouldn't get a manual transmission unless you have a burning desire to be shifting gears, the gm autos in our truck are very good and have provided many of us with good service, I have 170,000 miles on mine and still working fine, I had to replace a some sensors on it and run off a gremlin but the transmission it self has held up very good.

That won't work on a '94 unless it is a manual transmission or the key switch lock is broken. They have a lockout so you can't turn the key that far unless it is in neutral or park.

I pulled my steering wheel off and removed the lockplate to get at that electric contact that makes the key set off a chime. It might have changed my lock mechinish but I don't think so. It only locks if you pull the wheel while turning the key lock on mine. There's no lever to press to get your keys out.

Go try it on your '93 and you will see what I mean. (unless it is a manual transmission)

The 93 is a 5spd and it has always primed with ign. in on position.

Well.. i pulled the oil pressure sender.. found three wires on it.. took a guess and shorted the two outside ones.. and the pump started.. pumped it up.. bled it out..

took it for a drive.. everything seemed to be ok.. then took it to work this morning. .it started missing bad again. so i limped it back home.. haven't had a chance to look at it yet.

I suspect its the same problem..

I almost wonder if the bleed for the water.. if the hose has split or something.. last time i took the filter out the fuel was at the same level as the water bleed outlet on the resevoir.

hopefully this weekend i can get it sorted out.. gotta put a new engine in my car first though.. wheee..

but. then again. .that means the boost gauge comes outta the car and i can put it in the truck :)

-- WheatKing

ps.. i'm really starting to hate GM's.. hahaha..

Were it mine WK, I wouldnt' even replace the OPS, just let it run the oil gauge on the dash and run a seperate hot with key on circuit for your lift pump.

It still sounds like a leak. Look at the hose coming into the fuel bowl and the connector to see if the are wet with fuel. They tend to split around the clamps.

If there is air in it then the leak has to either be before the lift pump or a restriction after it causing the injsector pump to pull it in after it runs out of fuel. (which is what happened on mine)


While you have the OPS wire shorted out to run the pump, did you open the drain and see how fast it was coming out? I bet it is way too slow. It should be a stead stream that will shoot out 5 or 6 inches.


If the hose to the water drain had a leak, you would have fuel pouring off the bottom of the truck.

I had a leak in the fitting for the inline on the filter housing. It didn't drip any but the filter housing was full of air everytime I bled it. I removed the fitting wrapped it in PTFE tape and it has sealed to this day.Edited by: quantum mechanic

I had a leak in the fitting for the inline on the filter housing. It didn't drip any but the filter housing was full of air everytime I bled it. I removed the fitting wrapped it in PTFE tape and it has sealed to this day.


But was the lift pump working? It should have pressure there.

Yes, it was working. I can prime it under the hood and it required too much bleeding and priming. The truck would stall and I'd bleed 1/2 the filter housing of air.

Was that the line after the filter? If so, the filter might have been plugged enough to cause it.


If it has enough fuel volume, it should never have vacuum there. For it to let air in, it would need vacuum in the line. (caused by the IP trying to get more fuel than was available)

No, it was the line in. Every drip of fuel out must have let an airbubble in even under pressure.

Well..

good news and bad news..

Bad news.. tank must be full of crap..

took off the fuel bowl.. cleaned it all out..

took out the mesh screen in the IP and cleaned it all out..

blew out the lines to the fuel tank through the lift pump like someone suggested.. checked all hte lines and hte water bleed valve for leaks/cracks etc..

good news..

it goes like a scalded cat now http://www.dieselplace.com/forum/smileys/HiHi.gif

http://www.dieselplace.com/forum/smileys/Thumbs Up.gif to everyone who made suggestions :)

i like the truck again.

-- WheatKing

Where is the mesh screen in the IP? Thanks!http://www.dieselplace.com/forum/smileys/Big Smile.gif

where the fuel line attaches at the top.. there's a 17mm fitting you can take out.. it takes out a small mesh filter piece.

-- WheatKing

ARGH..

well..

it's dead in the water again.. went to take it out again tonight.. and it started .. ok.. and then idled fine.. then pulled it outta the driveway.. stuttered, missed.. pretty much almost died.. so i brought it back home and grabbed my trusty jeep.

my guess is the lift pump is dead / dying unless someone else has a better guess.

-- WheatKing

You said the pump was pumping when you jumped the connector. If you got one of those inline fuel guages at the autoparts you could verify pressure. TDG had the suggestion to put a clear piece of nylon inline to see if air is passing through the line.


Are you still bleeding air from the filter housing? You talked about replacing our OPS, Do you know if it's working now? If you can bleed the filter housing with the engine running it is.

The regulator Wheatking mentioned earlier is actually 3/4", but you can usually remove it with the 9/16 inlet fitting and remove the small screen on the bottom.


A weak lift pump will cause just as much trouble as an inop one, may supply enough pres/volume to idle, but hit the accel and it can't keep up. Truck idling, you should be able to crack the bleeder on top of the filter and hit the hood with fuel, if it just piddles out or if there is a lot of air present then change the lift pump. when you change it, inspect the two small o-rings on the inlet and outlet lines to the pump. A leak on the inlet side would let the pump draw air, on the outlet you would get a leak.

the way i have always bleed the filter after filter changes is to unplug the fuel sol. harness, put a piece of clear hose on the filter bleed, open it and have someone crank the motor until the air bubbles are gone(like brake bleeding). when it flows clear, close valve and stop cranking. reconnect fuel sol and start truck. may need to crank a little longer than usual. this process also applies to fuel system priming after running out of fuel which you really really don't want to make a habit ofhttp://www.dieselplace.com/forum/smileys/Ermm.gif

This relay controls my liftpump.


http://www.dieselplace.com/forum/uploads/CZF_relay.jpg


All I have to do to prime it is touch the two blue connectors together (One is common and one goes to the lift pump). I jump it with a small screw driver. the red connector is the OPS, which normally switches the relay to power the lift pump.


Cranking the engine on the side of the road might drain your battery before you start it. And nothing to disconnect. Edited by: quantum mechanic

Again, mine is simply on with the key on, doesn't get any simpler than that.

TDG, I like your way also. It's the cheapest easiest solution and it works. i would do it in a second if I had a OPS failure and wanted to pressurize the system.


The method I described is if you want to retain full OPS function and overcome the limitation of the weak contacts of the OPS by relaying the liftpump.

Mine failed on me, so I replaced it again and it failed a week later, I rigged this setup roadside as a temporary 'get me there fix', and decided I liked it better, nice to hear the pump running as soon as you turn the key I think.

I've been through three on the '94 and none on the rest. This is the only truck I've bypassed. I get lifetime warranty parts only so it works out when it fails, not if.

Well, I think everyone knows my thoery, if there's a better way, especially if its cheaper and more reliable, count me in.