Trouble cranking after mpfi injector swap

[GreenZ98]

I swapped the old injectors in my 98 with acdelco mpfi injectors recently and now its developed a cranking issue. Before the swap and for probably the week or so after if would crank as soon as you hit the key no hesitation or anything. Now when you try to crank it you have to hold the key and let it spin over for a good 5 to 8 seconds before it will crank. Could this be an issue with the new injectors or just coincidence that it started around the same time, although its never had any problem cranking before the swap.

 

[east302]

Other than that first long crank when the fuel lines were still dry, mine now starts instantly after updating the injectors.

I'd do a pressure test to see where you're at. Factory spec is 60-66 psi with ignition on, engine off. It should hold pressure for a few minutes after turning ignition off.



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[GreenZ98]

Other than that first long crank when the fuel lines were still dry, mine now starts instantly after updating the injectors.

I'd do a pressure test to see where you're at. Factory spec is 60-66 psi with ignition on, engine off. It should hold pressure for a few minutes after turning ignition off.



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Finally got around to doing a pressure test. Ignition on/engine off 56psi. Dropped to 54 after 5 minutes of turning ignition off and around 10 to 12 minutes to drop to 52. So it should be between 60-66? I've also read that 50-55 is factory spec or is that with the original poppet style injectors?

 

[badazzbulldog]

when you say spins is the starter engaging the flywheel?to me what your saying sounds like a starter issue

 

[east302]

60-66 is the factory spec for the original injectors. I believe it applies to the new ones as well. Your pressure is a little on the low side, so it may be the pump starting to wear out.

Has the fuel filter been changed since the swap? If not, I would change it out.

Here is GM's overall list of things to check for a hard start...

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And here are the diagnostics for the fuel pump pressure test...

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[GreenZ98]

Starter is working as it should just acts like it doesnt get fuel right away. I got ahold of the guy I bought it back from and he said all the time he had it he never changed the pump so I'm just gonna order one and change it next weekend. Maybe the new injectors working so much better than the old stopped up one just exposed that the pump was on its way out?

 

[east302]

I'd say that you've had a good run with the pump if it's made it 20 years.

Just in case you get lucky, I would still swap out the fuel filter if it hasn't been done recently. If clogged, it could be causing the pressure drop. A lot easier and cheaper than a pump...




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[GreenZ98]

I'd say that you've had a good run with the pump if it's made it 20 years.

Just in case you get lucky, I would still swap out the fuel filter if it hasn't been done recently. If clogged, it could be causing the pressure drop. A lot easier and cheaper than a pump...




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I actually changed the filter maybe a week before doing the injectors hoping that was the problem in that case because like you said much cheaper than injectors also. I'll replace it again with the pump anyway though. I greatly appreciate all the help and opinions guys, hoping to get all the mechanical stuff straightened out so I can focus on saving up to get it painted.

 

[shamrock246]

I have replaced everything in the fuel system and key on engine off pressure is 60 pump running and 58 when it turns off and 52 when the engine is idling.Not sure if the new style spider injectors require the original fuel pressure spec since the regulator is stamped with a rating of 420 kpa that converts to 60 psi so i don't how it would ever make it to 66 psi and i don't have my old spider to compare. I can't find an adjustable regulator that would work in place of the original one.

 

[moremudd]

Is it possible that the factory fuel pressure regulator is on the weak side now that the spider has the upgraded injectors instead of the poppet type . I also wonder if a connection isn't perfect in the engine harness plug on the upper intake manifold . I use a Elm 32 and the Torque app on my phone with blue tooth as not only a scan device but I enjoy the instant fuel economy feature , but it kept showing a brief moment of 225 miles per gallon , after pulling the injector harness plug apart , cleaning it and carefully using a very small amount of electrical grease it stopped showing that moment of 225 fuel economy , I never had a error code pop up or any other problems . I guess I wonder if you had something similar to monitor the difficult start up maybe something would show up ? Please let us know what ends up being the problem . This is the one I have been using since 2014 , there might be better ones now though . https://www.amazon.com/gp/product/B007PAHHWM/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1