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1991 350 TPI Injectors not pulsing

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1991 350 TPI Injectors not pulsing

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Old 06-12-2018, 10:28 AM
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1991 350 TPI Injectors not pulsing

Car has sat for about three years. It was starting and running, but ran horribly jumping all around. Brought it to a shop and had a tune-up done. Drove it home and everything was okay, but a few hours after it wasn't going above 30mph full throttle and rpms weren't going up. It started running horribly and began stalling out. Brought it back to the shop and they tried numerous things with no solution.
Tried the following;-ecu (twice)-distributor -fuel relay switchHad fuel pressure the entire time. No injectors are pulsing. Tried looking around for a solution, anyone have suggestions?
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Old 06-12-2018, 11:45 AM
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Re: 1991 350 TPI Injectors not pulsing

This is just a guess but assuming that your fuses are ok, check the grounding toward the ECU. Has to be either in that or the other end of the fuses toward the ignition. You will need a volt/ohm meter.


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Old 06-12-2018, 12:29 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by x55Cam View Post
This is just a guess but assuming that your fuses are ok, check the grounding toward the ECU. Has to be either in that or the other end of the fuses toward the ignition. You will need a volt/ohm meter.


Will see if that helps anything... Completely lost as to what the problem may be. Last resort is bringing it to GM
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Old 06-12-2018, 12:38 PM
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Re: 1991 350 TPI Injectors not pulsing

Also assuming of course that the shop measured constant fuel pressure when accelerating/revving the motor?
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Old 06-12-2018, 12:48 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by x55Cam View Post
Also assuming of course that the shop measured constant fuel pressure when accelerating/revving the motor?
Not exactly sure, but I was told it never once lost fuel pressure. Also, the car will still start on starting fluid stalling after a few minutes/running horribly. I assume fuses were checked by the shop since they said they literally tried everything. I've read if one injector is bad it may cause the others to not pulse. Asked the shop about that and was told they couldn't check each injector separately because none of them are pulsing
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Old 06-12-2018, 12:58 PM
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Re: 1991 350 TPI Injectors not pulsing

yes, one injector having a shorted coil could possibly affect those others in the same bank. You can easily check that by removing the connector to each one and use an ohm meter. Should get a reading well above 10 ohms.
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Old 06-12-2018, 01:46 PM
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Re: 1991 350 TPI Injectors not pulsing

What x55 posted, the stock OEM Multec injectors are a known failure point. The coils start to short out and the ECM can't drive any of them.

Only fix is to replace them.

RBob.
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Old 06-12-2018, 05:16 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by RBob View Post
What x55 posted, the stock OEM Multec injectors are a known failure point. The coils start to short out and the ECM can't drive any of them.

Only fix is to replace them.

RBob.
If that's the issue do you have any recommendation for replacement injectors? Not looking to spend an outrageous amount, but don't necessarily want to replace them again anytime soon.
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Old 06-12-2018, 05:19 PM
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Re: 1991 350 TPI Injectors not pulsing

Use the bosch, check with South Bay, they're members here.


Same problem with my 91 Z28, swapped them and problem solved.
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Old 06-12-2018, 08:44 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by PurelyPMD View Post
Use the bosch, check with South Bay, they're members here.


Same problem with my 91 Z28, swapped them and problem solved.
I recommend this also. I did in my car as replacements for stock (which were only 85k old), and in the truck as well when I converted it to TPI. People say that you'll have to burn a new chip tweaked for the injectors, but I never had to do that. Fuel trims look fine in both vehicles.
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Old 06-12-2018, 10:02 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by Pro View Post
I recommend this also. I did in my car as replacements for stock (which were only 85k old), and in the truck as well when I converted it to TPI. People say that you'll have to burn a new chip tweaked for the injectors, but I never had to do that. Fuel trims look fine in both vehicles.
yeah it seems to be hit or miss in terms of people needing tuning after Bosch III swap. But either way you end up with a far superior injector in the end... even if you need a tune it's very simple and well worth it.
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Old 06-13-2018, 06:45 AM
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Re: 1991 350 TPI Injectors not pulsing

Mine didn't need a tune - injectors are a little noisy but if you don't mind the clicking noise, you're fine.
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Old 06-19-2018, 02:46 PM
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Re: 1991 350 TPI Injectors not pulsing

After calling around trying to find the best shop for the price to change injectors they all tell me they don't think it's injectors that they want to look the car over. One shop also said $600 labor at $100/hr which seems outrageous. Read around a bit and it seems 4 hours is reasonable for changing injectors? Does anyone know what else commonly causes injectors to not pulse other than a bad injector? Also, how long would it take for the injectors to be changed?
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Old 06-19-2018, 02:49 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by RandyNJ View Post
After calling around trying to find the best shop for the price to change injectors they all tell me they don't think it's injectors that they want to look the car over. One shop also said $600 labor at $100/hr which seems outrageous. Read around a bit and it seems 4 hours is reasonable for changing injectors? Does anyone know what else commonly causes injectors to not pulse other than a bad injector? Also, how long would it take for the injectors to be changed?
Have you ohmed the injectors ?
Changing them is not that hard. 4 hours is too much labor time. Even if your slow I can’t imagine more than two hours. Get a t40 and 10mm socket and wrench and have at it.
Contact southbay08 (southbayfuel injectors.com )
For a great deal on injectors it sounds like you might need them.
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Old 06-19-2018, 02:54 PM
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Re: 1991 350 TPI Injectors not pulsing

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Old 06-19-2018, 02:59 PM
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Re: 1991 350 TPI Injectors not pulsing

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Old 06-19-2018, 03:25 PM
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Re: 1991 350 TPI Injectors not pulsing

While at it, do injector balance test also. The tester is cheap from ebay.

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Old 06-19-2018, 03:58 PM
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Re: 1991 350 TPI Injectors not pulsing

Why don't you disconnect all of them, that will rule out one of them taking out the bunch. Then you can connect a noid light and then crank it over and see if either bank fires. If they do that can rule out the ECU.
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Old 06-29-2018, 10:53 PM
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Re: 1991 350 TPI Injectors not pulsing

So I brought the car to a different shop than the last since they literally told me they didn't know what was wrong... This shop says the fuel pump and fuel lines are bad. On startup you can hear the fuel pump come on, could the fuel pump still be bad? Also, I was told around $700 for the pump, lines, and labor. Does that sound right?
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Old 06-29-2018, 11:01 PM
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Re: 1991 350 TPI Injectors not pulsing

Doesn’t sound like you have listened to any advice on the previous threads. On another thread a member was quoted $500 for a pump replacement. I’d do it yourself the hardest part is the exhaust being in the way.
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Old 06-30-2018, 03:09 PM
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Re: 1991 350 TPI Injectors not pulsing

Originally Posted by RandyNJ View Post
So I brought the car to a different shop than the last since they literally told me they didn't know what was wrong... This shop says the fuel pump and fuel lines are bad. On startup you can hear the fuel pump come on, could the fuel pump still be bad? Also, I was told around $700 for the pump, lines, and labor. Does that sound right?
Yes the pump could be bad. $700 is in the ball park with parts and labor. Very typical.

You really ought to look into doing some of this stuff yourself. Shops are going to rape you over working on something this old. Virtually this entire forum is for people that want/need to do that because shops are too expensive for the value of these cars. And god help you if you have corrosion problems on a 30 year old car. At my shop I have seriously considered adding a $5/Hr rider for every year older than 15 years just due to A: corrosion and hard to source parts, and B: previous buggery from owners or other shops that are clueless.

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Old 06-30-2018, 07:28 PM
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Re: 1991 350 TPI Injectors not pulsing

If you are handy with an volt/ohm meter and have access to one, you should at the very least, disconnect all the injectors from the harness and measure across the coils. Very simple and very revealing as to where to go from that point. All it takes is for one bad/shorted one to cause major problems.
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