89 4.0 cranking but not turning

Hay all. I have an 89 Lerado 4.0, i just replaced the air box with a cone filter, caped off the vaccume lines for the cold start stuff on the airbox, right now i just have the breather going into the engine compartment until i get it plumed.

That was 3 days ago, ever since its been taking longer and longer to start, and when it does it would bog and die, then fire up afte that. well now, its not starting at all.

The fuel pump turns on, i can hear it and i checked the relays, the filter is good, took it off, blew though it, its only 4 months old to begin with. The kicker is that i not getting fuel to the fuel rail. I'm a n00b when it comes to tinkering, yeah i can pull a chiltins and work on things, but before i go replaceing parts, i wanted to make sure my diagnosis was correct, Fuel pump: OK No fuel to the rail: bad fuel regulator.

If someone has a better idea im all ears... or even a way to check it/recondition the one i have so i dont need to repalce it, that would be great =) I was thinking about putting the airbox back in and make sure it wasnt that, but really, why would the airbox not being there cause th fuel to not get into the fuel rail... that dosent make sence to me... but yea... let me know =) Thanks in advance.

Ed

The fuel pressure regulator is on the front end of the fuel rail (it has the vacuum line going to it,) and the fuel rail feed is at the rear of the fuel rail. If you had a failed fuel pressure regulator, you would be running rich - not stalling out (the fuel pressure regulator is supposed to maintain something like manifold absolute pressure + 35psi, thus the vacuum line.)

What you have is an "intermittent: crank, no start" (just so you can describe it better next time. Typical "no-start" conditions are either "no crank" - the starter won't turn the engine - or "crank, no start" - the engine will turn, but will not catch. Entirely different causes, and it's important to let us know it's intermittent as well.)

What I'd like you to try doing is to start it again (you'll probably have to try a couple of times,) and then use the accelerator to bring the idle up around 2000rpm. See if that stabilises things - then my next suggestion would be a vacuum leak at the (probably) rear of the intake manifold (the screws work loose over time. If it's gone on long enough, a simple retorque job won't be enough - because the gasket has burned through.) An easy way to spot this one is to see if the stumble goes away after the engine starts to warm up - the aluminum intake flange expands and the join "magically" seals itself again.

It's also possible that your CPS is the culprit - intermittent failures of them are not common, but they're not unknown (of the five or six I've killed, one went intermittent on me.) The CPS is a bugger to replace - looking at the rear of the engine, it's at 11:00 on the bellhousing. You can see it just past the manifolds, at the rear of the engine, looking down along the firewall on the driver's side. It's easier to get to from underneath - use about three feet of extensions and a 7/16" or 11m/m (same size) socket with an inbuilt universal joint to get the screws off. Do not drop the screws in the bellhousing or you're boned! Packing the socket with either grease or bubblegum will help to hold the screws in place. (Gum can be removed more easily by putting the socket in the freezer overnight before trying to peel it out. Peanut butter can also work in a pinch - same treatment for removal. Peanut butter can also be washed out of the socket - use HOT water, and put the socket in the oven at 250* for five minutes or so to get it thoroughly dry.)

So, please do let us know if it's a "no crank" or "crank, no start" condition, and check out what I'd mentioned above. If you can get the idle to stabilise (or have a helper who can hold it up until it stabilises for you,) take a can of carburettor cleaner underhood and fog eveything that is a vacuum seal - if the cloud gets sucked in, you've found a leak.

Also, take a moment to examine (thoroughly) the ground strap from the firewall to the cylinder head. This can also cause you trouble, as it is the only ground point for the chassis, and compleats the ground reference for the ECU and engine management sensors (and is also the ground reference for the +5VDC signal that is used for the TPS and the HEGO sensors, and if those signals are wonky it can also cause a headache for you.)

Fuel pump turns on but no fuel pressure ? Odd.
I wonder if you take the feed line off the fuel filter and turn the key on does it spray gas all over for half a second the fuel pump is priming ? It should.
You can spray gas or ether down the throttle body too see how/if it runs ok/well/normal when you manually add fuel, to verify the fuel delivery problem.

Getting a late start, ill check the fuel pump again, and i thought the fuel came in the back side of the engine (as im looking at it) but it also looked like it was going in the front. I'll look at the ground strap also. and the issue now is that its not starting at all... as in turning over, it cranks, but dosent catch and run, it did yesterday morning, and i tried brining up the RPMs sometimes it runs like normal, other times it would bog like i was out of gas, once it died from that it would fire up normal again after a few tries and run fine until i turned it off again.

When i took the fuel filter off to check for clogs it was full of fuel, ill take it off again and see if the pump is actually pumping fuel, i assumed since the filter was full and i could hear it clicking on, that it was, but ill look again. Thanks for the advice guys, ill take a look and let you know.

Ed

Second thought if the pressure reg was stuck closed would it still be flooded? nevermind i guess it would, since the air in there would be pumped into the engine making room for the fuel, gotta love it when you ask and figure it out yourself lol... ok out to look at the grounding, pump and all that jazz... any more thoughts let me know, ill check back when i get in. Thanks again all =)

Ed

son of a... its the new fuel pump, i put it in a week before NWFest, it makes noise when the key turns on but i removed the filter and made sure it was pumping... and nodda... good times...

Well, that's one mystery less.

WRT fuel rail - the fuel comes in from the pump at the rear of the engine. The overpressure fuel goes out at the front, by way of the regulator. It's a "dead-head" style regulator, which actually controls pressure just after the point where it needs to be (don't worry - it works the way it's supposed to, it just seems like it shouldn't.)

Later XJ's use a "bypass" regulator, where the pressure is controlled directly after the pump and before the pressure regulation is needed. Neither system is "better" - but I do prefer using dead-head regulators, since they're usually easier to access...