Fuel pressure?

Tiny
TERMAXCO
  • MEMBER
  • 1987 CHEVROLET CELEBRITY
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
Car listed above is front wheel drive, approx 60,000 miles. Ran fine, then it sat outside for a few years, then would not start. No spark. Replaced ignition control module and it starts and runs fine except for these new symptoms:

Seems a little bit fuel starved sometimes on start; and, if depress accelerator to floor on start, or depress it fast to floor after start, it has a rev hesitation and most times (not all) it backfires once or twice out of the throttle body inj.(TBI) (sometimes a big fireball) then runs fine on idle and slow and partial acceleration or when holding steady at any RPM.

I have noticed the following:
1. There is no gasket on intake manifold (but it ran fine for years that way (I did take it off to get to module).
2. I do see pulsating fuel spraying in TBI while running but did not notice much fuel pressure out of lines at TBI (kind of a dribble) but don't visibly know how much is right. Does not have a fuel pressure check port in gas lines.
3. When changed old gas, the fuel pump in gas tank worked only when engine cranked but not when ign. Was only on "On". Took a long time to empty half tank.
4. Has two wires to top of TBI (one red, one blue) that the pulsing gas spray itself comes from. I do not know if I got these wires back on backwards or if that matters. As said, I do see gas spray pulses coming out into TBI from here. Course, not sure if its enough.

All seems to be related to a fast full acceleration. (And perhaps a sometimes slow start from too little fuel)

Finally, it does seem to maybe be getting just a “tiny” bit better as it runs? (After symptoms, I put half bottle of inj cleaner I had in half full gas tank with the new gas).
Any ideas what the problem might be?
Thank you
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Wednesday, April 7th, 2021 AT 11:33 AM

9 Replies

Tiny
STEVE W.
  • EXPERT
It sounds like the injector is partially plugged, likely varnish from setting, especially if it's improving as it runs the cleaner through it. Fuel pressure wise they run low pressure with 9-13 psi being normal. 13 PSI is the minimum if you restrict the outlet line for a second or two.
I would probably pull the fuel lines, spray them out with cleaner and pop the injector out and let it soak in cleaner overnight. Then blow out the filter screen and see if it's better.
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Wednesday, April 7th, 2021 AT 3:40 PM
Tiny
TERMAXCO
  • MEMBER
This sounds good. Will do. Thanks!

1. Am I right in that the round plastic piece (#6 in picture) on top of the throttle body with the two wires going to it (that fuel spray visibly pulses out of) is the actual injector that needs cleaning? Or, should I clean whole throttle body? And filter screen is in the fuel line? Or is there one in throttle body?

2. Getting the two wires put on wrongs sides of injector is not significant is it? (They came out of plug that keeps them straight.)

3. I reckon 9 to 13 PSI is visibly just a slight flow. Kind of spitting? So, if it comes to it, can I restrict the outlet fuel line to the TBI and then feel if it builds up some kind of pressure (in lieu of a pressure gauge since it does not have a pressure check port in the line)?

It did have an awful poisonous foreign chemical like smell from the exhaust when first started up. Like nothing I have ever smelled coming from a car. Not a rich fuel smell. It ran me out of the garage. I could not breathe it at all. Really bad and weird. It's cleared up now.
Thanks again!
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Wednesday, April 7th, 2021 AT 6:33 PM
Tiny
STEVE W.
  • EXPERT
You are correct on item one. Item two isn't a really big deal as it's nothing but a coil of wire inside there that pulses to open/close the injector. For the pressure you will need an adapter kit that connects into the fuel line at the TBI inlet. Many parts stores have the gauges as loaner tools or you can buy the common vacuum/pressure style units that were sold for years as the pressure is lower than many of the newer gauges will reliably read.
Then use adapters to connect it and see what you get. It should be a pretty solid stream of fuel out of the line, if you are seeing sputtering and spitting I would suspect the line is partially clogged with dirt and rust which is common with them when they set.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

That car does have an inline filter that isn't hard to replace, it's under it to the left of the tank. If the lines are in good shape the filter should come off okay, you can also check fuel pressure there as well as flow and fuel quality. But it's usually easier to check the pressure at the TBI.
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Wednesday, April 7th, 2021 AT 6:58 PM
Tiny
TERMAXCO
  • MEMBER
Thanks again. Great help. Yep, at first, I did only have a sputtering/spitting gas line at the TBI - very weak. But now its a full steady stream. And a full stream out of TBI with injector removed. So, things are getting better and we are down to the injector itself I guess.

1. Or, could it be the return line clogged?

2. Since, the hesitation and backfire happens only on full fast acceleration, what instantly boosts the fuel to match the instant extra air? I see only the same 3 injector holes (I'm old school. Carb with carb pumps).

3. Also: Does the injector have any inner seals or parts that I need to watch for or protect when soaking?

4. Will it also need to be hooked up to current and pulse to finish up?

Thanks!
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Thursday, April 8th, 2021 AT 10:02 AM
Tiny
STEVE W.
  • EXPERT
Good to hear it has a full stream now. I would still check the pressure because low pressure could easily cause the stumble when you hit the gas.
The injector flow rate is controlled to add the extra fuel. It works using pulse wave modulation. To increase the fuel the injector is pulsed open longer. So (using imaginary numbers here) say at idle it pulses 2 times a second , when you hit the gas the airflow increases and the PCM starts pulsing the injector at 60 times a second. It also switches the control method from closed loop to open loop during wide open throttle. Works sort of like the old school accelerator pumps combined with the power piston in a Holley as the drop in vacuum relaxes the regulator to let more fuel flow. If you haven't already you may want to replace the regulator guts with a kit, they can get stiff and not move as free as they should.

Only thing on the injector is to keep the connector out of the cleaner and get new o-rings for it. If you have a way to pulse it while it is in the cleaner great. A simple 12 volt pulse is all that's needed, I've used a 9 volt battery and a couple wires that get touched to the terminals rapidly. You don't want it locked open as that can damage the coil in it.
If you like electronics you can build a tester yourself.

http://hackaweek.com/hacks/building-an-electronic-fuel-injector-tester/

They are handy to test injectors on many things, and can be used for other things as well.
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Thursday, April 8th, 2021 AT 11:23 AM
Tiny
TERMAXCO
  • MEMBER
As I mentioned I'm much more familiar with carburetors, so enjoying learning. Thanks for explaining things.

Will make an injector tester. Will check fuel pressure. And, will fix up
fuel pressure regulator.
It's in with the throttle Body correct?

Should I eliminate the lack of an intake manifold gasket as a possible cause?
Thanks!
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Thursday, April 8th, 2021 AT 2:45 PM
Tiny
STEVE W.
  • EXPERT
I would get the regulator rebuilt, yes it's the black item in the image on the front of the TBI. If you don't want to build you can get one off amazon that does the job, it's usually about $40.00.
I would replace the gasket to at least eliminate one issue.
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Thursday, April 8th, 2021 AT 3:05 PM
Tiny
TERMAXCO
  • MEMBER
Thanks.
New development. I soaked and spray cleaned injector. Put it back on with the 2 coil wires hooked up etc. Instead of the former normal looking amount of fuel, in only about 3 cranks and 2 seconds it instantly shot out gas filling up the entire throttle body and flooding plugs; When took plugs out, it shot solid stream of gas out the first compression opening about 2+ feet.
What do you think happened? Think I messed up the regulator when I checked to see if fuel coming into throttle body without the injector in it.
New injector now, or regulator you think? I wish I knew what I was doing? Hee hee
Thank you
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Friday, April 9th, 2021 AT 10:47 AM
Tiny
STEVE W.
  • EXPERT
I would check the injector O-rings and the screen. That and look at the nozzle area of the injector. For that much fuel it almost has to come past the seals. A new injector and the regulator kit isn't a bad idea, but I would try to rule out just bad seals first.
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Friday, April 9th, 2021 AT 5:56 PM

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