Ok so I better explain this 1998 Jimmy 4dr beast. I bought it with a blown tranny and decided to put a standard in it. So once I got the bugs out (almost) of that change I decided a Mr. Lube trip was in order for fresh fluids blah blah. They broke the line to the fuel filter resulting in the fuel tank needing to come out resulting in the recommendation of a new fuel pump(yup they got me). Since that point the truck has had occasional stumble/almost misfire but with no consistency other than low’ish rpm(-2500).
so onto my next brilliant idea, I thought perhaps there was a poppet valve issue causing the drivability issue so I upgrades to the next generation spider from Motorman. Well I finally installed that and it is now worse, bad idle, stumbles on the road and hard start. So I’ve checked the fuel pressure and it will spike to 60 then down to 55 and then 52 while running. If I pressurize the system and wait the 3minutes it will read 25-30 psi. I have 19 hg vacuum, it was 20 when I last checked.
So I’m thinking Mr.Lube put in a cheap pump for a X engine which is why it had the issues.

My question here is would the newer spider injectors react as I described when not enough fuel pressure is provided?
thanks for any help fellas, I know it is an oddball situation. And if a new fuel pump is needed then what year for the new style injectors?

Shawn

 

The newer MFI spider should be more compliant to a wider range of fuel pressures than the older SCFI spider with it's pressure actuated poppet nozzles. Fuel pressure will affect the atomization of the fuel out of the nozzle, but given that the electronic injector is located in the intake runner directly connected to the nozzle on the MFI spider, it will always spray fuel regardless of the pressure unlike the SCFI spider which would just stop if pressure was too low.

It sure does sound like you have a fuel pressure problem in the system that you need to track down and take care of. Your leakdown is excessive so you'll need to determine whether that is in the pump or in the spider. There are two fuel pressure tech articles that should be able to help you get that determined. Since the problem was present before & after the spider, I'm going to take a guess that the pump is at fault, but proper diagnosis should be done to confirm.

A cheap pump is a cheap pump and they usually cause more problems than the savings are worth. There is not a specific pump required for the MFI spider. A stock replacement pump will work with either spider equally as well.

 

Thanks very much for the reply Swartlkk. I woke up thinking ‘I need to use those fittings that came with the fuel pressure tester to check at the fuel filter’. I’ll check when I get back home On Saturday

 

ok so I did a pressure test at the fuel filter. Pump cranks up to like 90+ psi down to 75-80 after 3mins and 65 at the 10minute mark. So I’m thinking that remanned spider has an issue.
thoughts?

 

I would agree. Per the specs, your pump tests okay in both max pressure and leakdown rate.

 

so as an update, I did find one of the rail body wires bent where the injector plug is. Straightened that and replaced complete spider with new and it is right as rain. Waaaay better than it has been in my possession. There was a puddle of fuel sitting on the rear part of lower intake directly under the fuel regulator. So not such a good job on the ‘remanufacturing on Motorman’s part.
ill see if they will ship me another regulator.
Jimmy gets better!!

 

I was told that there are specific ways the injectos are to get bent on the new ones, ive been trying to find an instructions manual, would you be able to shed some light?

 

they are numbered on the central rail , from there I just tried to match what the old setup had for bends. Really have to be gentle with the bends and a heat gun is a must on a new setup.
if you haven’t done this already I can post pics of my backup spider Don

 

If you don't mind. I didn't know about the heat gun. So will have to get that pulled from storage before I tackle this.

 

here you go Don