94 CPI vortec fuel pressure question
 

I have been doing work on my fuel system, had a run in with the leaking regulator. First time i installed it it was set to 90 psi. With the fuel pressure at 90 it ran REALLY rich but better than it did leaking. Well i set it to with the pump going engine off at 58psi. Bolted it back up an noticed that in normal operation of key on engine off it's 58psi till it clicks off then drops to 48-50psi. Holds steady, it also runs at 48-50. Idles ok, can feel a miss here and there. 17-18 mpg. Full throttle does good but you feel a bog, actually its more like you dont notice it being sluggish till it kicks in with full power and you can see what you've been missing. Does this randomly while driving but driveable. Is any of this normal? Should i up the pressure setting at the regulator again to 58 after the pump shuts off instead of when pump is running? There are no leaks under the upper plenum (poppets, lines, lines from injector to poppets) made sure of that when i sealed it back up. Maybe my fuel pump is weak from running at 90 psi for so long? Any suggestions? I really just want to know if i set the fuel pressure right or not.

i would set it to about 60 to 65 psi. have you ever heard of sea foam? it works wonders. you just pour small amounts into the brake booster line. use about a cup worth and when your about finished sucking it all up, just pour it all in fast to kill the engine. if it doest die then hury and shut it off. wait 15 min start then rev to 3 to 4 grand untill smoke clears. it cleans up all the carbon build up and gunk. makes the idle more smooth.

also get some carb cleaner and clean the throttle blade. they get pretty gummed up also and can cause poor idle.

I have used seafoam before. I cleaned the upper intake out last time i had it off when i did the regulator. I was thinking about raising the fuel pressure a little but my main concern is the fact that when the pump is on i read 58-60 and the second it shuts off it drops to 50 and holds realatively well. Is that normal?

I have a video.

YES thats totally normal. if it holds at 50 or even around 40 for 20 min then its fine. ALL OLD s10 blazers will have a miss now and then. because they use a single injector that fires every compression stroke no mater if the intake valve is open or not. the newer spfi engines like in the 96 blazers or 95 pickups injectors fire only on one intake stroke. fires ONCE per cylinder intake stroke. maby somebody else can clear this up since yea a bottle of vodka goes by quickly in my house. lol. but yea even mine misses a little at IDLE only. when i rev it up its BEAST. but id still turn up the regulator just a few PSI. make it so when it shuts off its around 55 to 50 psi. and when its running make it to where its at 60 psi. dont go above 62psi or lyou might damage the injecor but highly unlikely. also in the video it sounds like you have a vacuum leak. might want to check that out also. go to your parts store and rent a vacuum gauge. leave all the vacuum hoses hooked up and install a t conector in the kit you rented. should be 18psi or close to give or take 2 psi

I have fixed all my vacuum leaks long ago, it had about 16-18psi. What you hear is my short ram intake. The filter is about 2 inches from the camera, lol. I had one of those cone filters lying around and slapped it on. I dont think a tad about 62psi fuel pressure will kill it if me running it at 90psi for a month didnt... I'm gonna turn it up and see what happens. Right now if i floor it there is a 50/50 chance it will be sluggish or fast as hell. It's real annoying. Plan on turning it up a few psi this weekend, might push it off a little cause i scored a brush guard for $30. :icon_smile: Gotta put it on

yea i wouldnt assume its a injector problem. i would like i said tune it to 60 psi. and leave it. i have the ram air intake also if you look at my youtube vids. it sounds pretty cool and i have noticed a bit in low end torque. when running it should be 55 - 60 psi. but when on highway and you hit the gasss all the way it will bog for a sec or two then kick in and bam you will be past them them in senconds. lol

Pressure is too low. Bump it up to 60

This.

Ok, but do i set it to 60 while the pump is running or try to get it to 60 after it shuts off? It runs at the psi it drops to after the pump cuts off like in the vid. That's what i'm wondering

60psi when its running.

Boosted it up to 60psi when the pump is on. Alot of driveability issues are gone. It used to hesitate before a shift, now it doesnt. And the bogging is gone. It still leaks down to 50ish quickly and once again no visable leaks under the plenum so im thinking a fuel pump is in the future.

thats good to hear. im glad i could help. if you ever have to replace the pump and you only replace the pump instead of a whole new sending unit, then make sure you also buy 3in of 3/8 gas line. it goes from the pump to the sending unit. they usually get pin holes in them and leak. but if your holding a steady pressure at 60psi then it should be fine.

The thing is it doesnt hold at 60psi. Immediatly after the pump shuts off it drops to 50psi then drops only 5-10 over an hour.

Sorry I cant help with your fuel pressure problem but as far as the mis goes it could be a number of things other than an injector.You may ave carbon built up inside your distributor cap/rotor on the electrical contacts.EIther replace or sand all the corrosion off with some light grade sand paper.Seems to be a common issue on my truck anyways.Check your plugs and clean then regap them.Check your sparkplug wires as well.This could be a salution to your bogging down problem.One other thing did you check the openings at the end of poppets they could be plugged up,this would cause a miss and lack of power.Best of luck hope this helps.

I guess i didnt say that after turning it up to 62psi it doesnt bog anymore. Also the whole ignition system is new, even the distributor. The old one had some worn out gears and let the timing just around. It runs good for the most part, I think I still need a new fuel pump. Pressure still drops and there isnt a leak under the intake.

yea thats fine if it drops to 50psi when key off and holds. if it only drops 5/10psi over and hour then thats great. no problem in the fuel system. its all good.

So, here is an update after i adjusted the fuel pressure to 60psi. The needle isnt erratic like this when the truck is cold, only after it has run for a while. When cold it's similar to the first vid only it hovers at 60psi instead of 55. I only decided to test this becasue after its warm the idle is unstable, it will drop real low, then go back up, and so on. It can level out every now and then but if you snap the pedal for a second it almost dies then saves itself, then tries to die and so on. It's like it doesnt know where to idle.

i would change the fuel filter next and see what happens. ive seen pumps die because of a clogged fuel filter. happened to my bravada. pump went out and put a new one in and ran like crap poor idle and highway driving was really bad. changed the filter and now no problem for over 2 years.

with a clogged filter the pump works overtime that might explain the eratic pressure and bogging down. my 97 bravada did the same thing with a clogged filter.

Sadly Ive already replaced the fuel filter and the old one seemed ok. I've been reading about people having similar idle issues with the egr being plugged, i think im gonna start there. Its one of the few things i havent checked out. Vacuum is around 16, mayne a tad low but didnt seem that low. Im also wondering about the cat, when the rpms drop low like it wants to die the exhaust sounds funny, and when it catches itself and revs up the exhaust is really hot, i know its normally hot but i mean its burn your hand if your to close hot. Last time i experianced that was with a clogged cat. But that car wouldnt exceed 2500 rpm, mine drives fine. Stomp the gas the thing flys. Its important to know the rpms never seem to go much higher than normal, it just dips down like it wants to die.

dam... hmmm yea check the egr make sure the pin moves in and out freeley. before you put it back in when you have it off turn the truck on for a few seconds. it will rev pretty high and be loud but it will blow out any carbon thats in the ports. if the egr is sticking open just a bit from carbon or whatever it will let excess air and exhaust in unmetered. so yea check the egr. and make sure to spend the extra few bucks and get a gasket for the egr that has a screen in it. most likely they will have to order it at the part store but should get it in next day.

Did exactly that with no difderence. The valve had a little black build up on it, it moved freely. Seated good. I still cleaned it up but there wasnt much to clean. No chunks. Installed a screened gasket. No change. A friend of mine said my exhaust smells like my cat is bad, ever since the weather got cold my sensamellsmell is useless. My cat has had a hard life, this wouldnt surprise me. Gonna try running it with the o2 sensor out. Also OBD 1 scan tool is on the way, maybe it can tell me something. Yes it shows live data.

Well, I took the o2 out of the exhaust and the truck had me fooled for a second casue it ran smooth but then started lopeing again. So I dont think a clogged cat is my problem. However almost no exhaust was coming out of the end of the pipe when i did this, someone told me if all the exhaust starts coming out the o2 sensor's hole if my be clogged a bit. IDK if that's true. Not touching crap till i get that scan tool in unless I hear a really good idea.

does it have low power? backfiring maby. you said before it was running really rich. maby the coil is going bad. happened to me. replaced the whole injecter assemble and the lines and still ran bad. idle was terrible. watch this vid of mine and see if it sounds like mine. and im pretty sure obd1 doesnt have live data and will only show you trouble codes when your engine light is on.

Ever since i turned the fuel pressure up to 60 it has great power going down the road. Which is what is bugging me so much. I can still try to swap the coil out, i have a spare. The coil is new, I replaced it a while ago when i was having problems timing the truck, the old one was good (of course didnt know that at the time). I also have a spare set of injectors i just cleaned up and may put in just to try. Other than that idk, i'm not sure if my exhaust system is actually ok. I hear the exhaust sound odd like a miss but the engine doesnt seem to skip like the exhasut does. Like a partial clog. It sounded smoother when i had the o2 out to allow an extra path before the cat. It said on the item description, "Equus 3120 Innova Diagnostic Code Scanner with Freeze Frame Data for OBDI and OBDII Vehicles". Rather that's true or not I guess I'll find out.

Well a new discovery, after a drive I popped the hop to check if my new water pump seals were holding pressure (it was) and i manually hit the throttle by hand. I heard a soundd out of the intake like a growling or low popping sound like I had heard before when i had the timing off a long time ago (advanced I think, not sure). It's not a backfire. Now I turned it off, put my tools up and a friend showed up. When i restart it the noise isnt there anymore. But after a few drives since then I've verified after every drive it will do this and if shut off and restarted it is back to normal till you drive it a bit. So something is adjusting my timing to a point it shouldnt be i'm guessing. Knock sensor? I'll check my base timing tomorrow when i'm home. Currently at my girlfriends appt. and they dont like people working on cars in the parking lot. With everything i've tested so far being ok, wondering if the computer has taken a crap?

So far new parts are:
complete distributor
coil
plugs
wires
fuel pressure regulator
bunch of vacuum lines
water pump- leaked from seals, may as well replace old rusty while in there
thermostat-old one opened to late

Tested
TPS-ok
MAP-ok
EGR- cleaned and screened
IAC- cleaned niether were dirty
Ect and iat tested good
vacuum is at 17 at idle drops during loping spells
fuel pressure is at 60psi key on engine off
PCV valve rattles

Anybody know how to test an o2 sensor? or a knock sensor?

I think for the O2 sensor, you need the scanner hooked up and you run the engine under load to make sure the scanner shows the o2 sensor reading rich/lean rich/lean rich/lean rich/lean and so on. If not then probably needs to be replaced. You mention engine pulls 17 inchs vac. at idle. Is that what its suppose to be?

I think 16-20 is acceptable for vacuum. Im going to try to figure out a way to test the o2 with my multimeter. Whay struck me as odd was when i had it unplugged from the exhaust stream and ran it, it never threw a code. I didnt run it that long but it was for a few minutes.

yea taking the o2 sensor out of the exhaust wont throw a code unless it was warmed up to operating temp 190f. the computer ignores the o2 sensors before it reaches 190f. do you think its still running rich?? if so try replacing the engine temp sensor. its right by the water pump oulet to heater heater core. that controls the amount of fuel it gets depending on how hot or cold the engine is. also if you think the cat is plugged then drill some holes into the belly of it. it will make it a little louder but no more than the o2 sensor being out. the knock sensor could be bad and throw the timming off. try unplugging it before you start it and see if it smoothes out. cause it should just default and run like its supposed to. the connector might be corroded aswell.

So, scan tool doesnt view live data. Bummer... but drove all day with the o2 out and it is running great, just loud. It threw a code only on the first drive. Lean code 44 as expected but all other drives the light never came on. Im spraying pb blaster on the cat bolts every time i get somewhere so i can take it off to check it out. I plan on checking my o2 sensor as well cause i think its odd that it didnt throw a code but once while unplugged from the exhaust. Ect sensor was tested and was reading good as well as the iat. It doesnt seem to be running rich.

Good news and as embarrased as I am to admit this it was my fuel pressure regulator. I picked up a spare spider from a junk blazer a guy was using for the doors and some interior pieces. The truck blew up from a blown head gasket so i figured the spider injector would be fine, well it was :icon_teeth: ! So anyway took off upper intake for the 1000th time and the FPR was dripping fuel and that side was all clean and shiney. Swapped spider assemblies and now it even holds pressure completely. It used to leak off very slowly. Problem seems gone, truck idles smooth. Very very VERY slight miss in park or neutral but i may have a fouled plug due to all the leaking. From what i understand the excess fuel leaks into cyl 5, so i'll check that plug out. But problem solved, another reason not to get cheap parts... stupid Dorman FPR.