Hope someone can shed some light on this. Ihave searched and read hundreds of posts related to fuel pump problems,my 98 Jimmy was throwing PO300 and PO175/172 codes,did the normal cap, rotor, filter, plugs, seafoam, Mobil1 oilchange after seafoam. Stopped PO300 but would still get PO175/172. Saw posts w/low temp issues maybe causing rich condition,changed out t/stat. to a new Stant 195* also flushed heater coreput in correct coolant and bled air. Helped the roughidle and seemed better inoverall running condition. Got a Eqqus fuel pressure tester on E-bay and figured I'd try it out, pressure @shrader valve is 57#-58# KOEO drops out to 4#-5# immediatelly after pump shuts off. Pump Bad no problem right? Decided to check at filter , disconnected line @filterfrom tank hooked up pressure gaugehad slight leak on plug @ hose end, fixedleak and turn KEY ON ENG. OFF pressure went to 75# and bled down to 25# over 5-7 min. WTF! amI missing something in the other posts I read or is this just anotherone of these erratic fuel pump issues. Is it a fuel return line blocked?, if so is there a good (re: foolproof) way to clear a clogged line. Or could it be a bad fuel regulator? Sorry if this is a little disjointed but IHAVE used the search alot and am posting for the first time. Hope someone can point me in the right direction as I have read about many others getting great advice and feedback from you guys! DAVE
1998 GMC JIMMY

 

Check out THIS POST in the DIY section for fuel system diagnosis on the newer SCFI motors.

If it bleeds off quickly, it would indicate that the FPR is at fault. The link above goes through the checks to narrow down the source of the problem.

 

Thank You for the quick reply I saw the check list and did look at some of the info before posting but now i will do a more thorough system check. BTW where in the factory manuaul is this diagnostic chart located I have the 3 vol. 1998 gm Factory service set and looking through it I couldn't find it, would make it easier for me to bring it out to the jimmy and save the paper by not printing out.
thank you
Dave 1998 GMC jimmy 146000 mi.

 

Also sorry for the ommision from above post but if you dont have the adapter to check the fuel pressure after the filter by the dissconnect for the return line, can you hook it up to the shrader valve and un-couple the return line and look for blockage that way? Or do you haveto aquire the adapter to get a true look at what is happenig with these tempermental fuel systems. I don't mind buying the fuel pipe shut-off adapter but is it a GM only part or can you get it aftermarket J 42964-1 is the part # i believe,thanks again. Dave

 

I have never used that adapter, but then again, fuel system problems have typically shown up and been narrowed down with out that particular test. As far as where that trouble chart is in the FSM... I am not sure. I do not have a FSM for the 2nd gens any longer. I would imagine it should be in the fuel system section somewhere.

 

Swartlkk Thank you for pointing me in the right direction. I am going to replace the spider wMFI upgrade from GMPD, when reading through MFI Upgrade post you said the bracket that holds the spider on the2000 blazer was the same as needed for theMFI upgrade do you know if the bracket on my 98 Jimmy will fit the MFI upgrade? TIA.
Dave 1998 Jimmy 14600 mi.

 

My last post even confused me! OK this is what i have determined , fuel pressure regulator is bad. If I am tearing down the intake I want to go ahead and do the spider "upgrade". My question's are, will my bracket currently holding the orig. spider fit the "Upgrade" and if NOT are these the only parts i should need to do the job right?
GM# 12568332 sequential multi port fuel injector
GM# 88894355 sequential multi port fuel injector bracket
GM# 17113215 sequential multi port fuel injector seal kit
GM parts Direct says addl. "may" be needed, can you tell me what could be changed or needed when I tear this down? I will get some of the parts online and get whatever I may need local if available to ease returns if I don't use them. Also Best Buys 4 Parts.Com is where i have found the best price for the spider, has anyone hadany dealings with them? If so how was your experience?
Dave 1998 GMC JIMMY
146000 mi.

 

I did not need to replace the bracket when I did the "upgrade" on my 2000 Bravada and I do not believe that any 98+ truck would need to. The seal kit is unnecessary as well as all of the seals required for the spider are included with the new spider.

I got a great deal on the spider from my local dealership. They actually work with you on the price. They could not do it for the GMPD.com price, but by the time you put shipping and handling (outrageous from GMPD.com), they were cheaper and they had it to me in one day. Of the other online parts stores, I have only dealt with Parts4Chevys.com and they were great.

If you order the parts from the dealer, you could always return the bracket if it turned out to be unnecessary.