I have a 88 5.7 TPI. I recently changed my injectors with Delphi replacements along with the fuel regulator diaphragm. The car actually runs a little worse than before. It wants to stall when starting and stumbles when revving up. I checked for vacuum leaks and can not find any. My fuel pressure is good but goes to zero seconds after the pump is done priming. When I pinched the return line to test the fuel regulator as I read on another post it holds pressure. Is the fuel regulator not holding pressure the source of my problem? Also, is there a way to check for a vacuum leak using a gauge? Thanks in advance for any help.
I think you can get a general sense of a vac leak with a gauge. if its a big leak. another way is using a smoke test. how long have you been running since the injector change? you're computer will self tune a little bit over time, and may fix this. the TPI will typically will stall a little bit when it goes "closed loop" on cold engine start, like a little gasp, before it smooths out again. but not on warm start, it should be smooth and stay smooth. you should not lose fuel pressure very fast after shutting down the engine. if you are, then something is probably wrong there.
It sounds like your regulator is bad since pressure from the tank to regulator would be controlled by the pump, injectors and regulator.... since you are pinching off the return line and its holding... that would likely mean the regulator you put in is defective
Another possibility is the injectors you put in could be slightly different size. I mean its pretty hard to get an exact exact replica of an injector from so old to something new. Like the delay and lag times could be different. And furthermore if the ECU is using old memorized fuel trims it would be way off.
obviously work on the regulator situation first. But after that I would force open loop (Disconnect Oxygen sensors) and compare the behavior of the engine open loop vs closed, it should run pretty good in open loop. If it doesn't run well in open loop you might need to throw a wideband on it and dial up or down the fuel pressure to make the engine happy again. Then put back into closed loop. This all assuming the lag times of the new injectors will adequately be governed by the ecu, I don't see why not but its something to watch out for.
Thanks everyone for the replies. A couple of things to note: I replaced my injectors with the more expensive Delphi 22# ones. I only changed the diaphragm in the fuel pressure regulator. It was part of the kit I bought and was orange in color. Is there a better diaphragm to buy? Also, would a bad diaphragm cause the issues that I described. I also only started the car a few times and drove it two miles. Do I need to drive it longer to let the ECU relearn itself? I also disconnect the battery numerous times when working on it. Is this adding to my issues. Sorry for all the questions but I'm really new to the TPI world and trying to learn
I don't really understand what you mean by this "My fuel pressure is good but goes to zero seconds after the pump is done priming. When I pinched the return line to test the fuel regulator it holds pressure."
What are you doing to measure fuel pressure?
Are you certain your injectors are seated properly? I used the Black Delphi's on my car and they work like a champ. Yeah, I don't think 2 miles is enough to learn fuel trims, but it sounds like you are really far off. start with the simple stuff first and rule them out.
If you are measuring fuel pressure, and you can see it climb to 43 or what ever it should be, and then as soon as the pump stops priming (engine still off) and your fuel press drops to zero, then this is obviously your problem. something isn't keeping the pressure up. Basically, the injectors are nothing but valves. When the valve opens, fuel sprays out. Then it is closed. If no pressure, no spray, just a drizzle.
I don't really understand what you mean by this "My fuel pressure is good but goes to zero seconds after the pump is done priming. When I pinched the return line to test the fuel regulator it holds pressure."
What are you doing to measure fuel pressure?
Are you certain your injectors are seated properly? I used the Black Delphi's on my car and they work like a champ. Yeah, I don't think 2 miles is enough to learn fuel trims, but it sounds like you are really far off. start with the simple stuff first and rule them out.
If you are measuring fuel pressure, and you can see it climb to 43 or what ever it should be, and then as soon as the pump stops priming (engine still off) and your fuel press drops to zero, then this is obviously your problem. something isn't keeping the pressure up.
I have a fuel pressure gauge attached to the fuel rail. I turn the key on to accessory, pump primes for 2 or so seconds and I watch the fuel pressure climb to around 42 psi. Immediately after the pump shuts off the pressure steadily falls to zero. I read on another post to pinch the return line and if its hold pressure than your regulator is bad. Does this sound correct or did I miss interpret it? I also read on that same post that as long as the pump is keeping up with the engine running than it isn't an issue if it drops off. This is where I'm confused. The car ran well prior to the injector change except for when it was warm it would take longer to start like it was flooded. The only thing that has changed was that I took it apart, replaced injectors and the regulator diaphragm. I cannot find any vacuum leaks so I'm down to injector or regulator problem.
I don't happen to have my book with me (or my car) to specifically recall how this works, but intuitively the fuel rails should retain pressure. If you are holding the return line closed, and the fuel rails subsequently DON'T lose pressure, yeah, it sort of sounds like the regulator is not holding pressure as it should. Is the regulator involved in allowing fuel go down the fuel return line? This is the part I don't recall, but it makes sense that it would. If all of that is true, then it really does sounds like a regulator issues. Torn rubber or bad spring? or installed backwards? (not even sure if that is possible) Been a while since I looked at all of this.
The key sounds like since you hold the return line and pressure remains, you can rule out it being a fuel pump issue. sounds like the ol' pump is trying its best to keep up, cause your car drives.
by the look of this diagram, the fuel return line does run to the pressure regulator. #224 is the clue. looks like other valves on the car's fuel system. pretty simple, just a plunger type valve that moves up and down, and the spring controls the pressure. if the spring can't hold the pressure, it probably opens up and allows fuel to return. If the plunger is torn, or not seated correctly, fuel will leak past and also go back to the return line. if installed upside down (unlikely) it works in opposite of what it should.
Thanks LB for the diagram. I did not put the regulator back together as I was cleaning the manifold off when my mechanic friend rebuilt it. I can't imagine him putting it in wrong so I'm not really sure still if this is the problem If you look under the 3rd thread on the TPI postings you'll se a post from Big Chief titled "fuel pressure not holding". Look at the first reply and this is where someone describes pinching the return line to troubleshoot. Thanks so much for all your help.
it makes total sense that if you squeeze on the return line, and your pressure begins to hold, something upstream of the return line is failing. it really sounds like your pressure reg is the issue. if it was your injectors leaking, the pressure would not hold when you squeeze return line. if it was your fuel pump leaking, again pressure would not hold. that's about all there is besides a fuel filter.
when you get all this apart, now that you have a way to attach fuel press gauge you can test pressure before putting on intake next time.
Take a close look when apart at sealing surface on regulator body seat.
I’ve seen what looks like nick that will allow the regulator diaphragm metal seal off the return line port.
When i changed the fuel regulator in my V6 the pressure held. When the regulator failed, it would act the same as yours and not hold pressure...... .for how cheap it is, Id just get a good quality regulator from ac delco and replace it yourself and see if that helps anything. Is it a trusted mechanic that put it in? Or are they questionable and possibly didn't change it? All you need is the security torx bit to change it.
Is it firing on all cylinders? Spark plugs soaked in gas? you could have got a bad new injector out of the box... i have before! even a good brand like Delphi!
If the fuel rail says 44 or 42psi or something near that while the engine is running, the engine should run normal. It shouldn't matter if the return leaks down to 0psi when the engine is off.
They sell fuel pumps now without check valves that cause fuel pressure to drop to 0 when engine off. It isn't an issue. Just an annoyance. I would not think diagnostically it would matter to the engine's performance as long as the pressure remains at steady 40-44psi during operation.
I think your engine performance issue is elsewhere. Injector size or injector leaking. I would look at plugs for fuel, sign of injector leaking. Prime the fuel system on a cold, OFF engine, then check each plugs for sign of fuel, one might be full of fuel and wet smell like fuel because of injector leaking through an O-ring. Pretty common if you didn't lube the orings with vaseline on the way in.
use motor oil on injector o-ring when installing, you don't want to inject foreign materials into the combustion chambers or exhaust stream. could be bad for cats and o2 sensors. oil is expected. so is gasoline, but nothing else. oil better lubricant than gasoline.
