1989rocg92

Hello everyone. The fuel pump in my 1990 Formula (5.0 TPI / 5-spd) recently started losing pressure while running..would just slowly bleed off until it stalled. Installed new GM/Delco fuel pump (EP 241) with new Spectra Premium sending unit (the old sending unit was reading 7k ohms..YIKES!..so couldn't tell how much gas I had..figured might as well change it). Anyhow..new pump/sending unit, and fuel filter installed...running pressure is fine, about 42 w/ adjustable reg...but system does not hold key off pressure for nothing. Pinched off the feed line after pressurization..and holds like a champ (indicates injectors, regulator are OK). Unclamp the feed line..drops like a rock (down to 0 in about 15/20 secs). Seriously??..bad check valve in new pump?? Anyone experienced this before..and is there anything else I should check for? I did use the supplied connector hose (pump to sending unit) in lieu of the pulsator/damper, which was never an issue in the 4 other pumps I have done in the past on my Irocs. I put a jumper on the relay terminals to run the new pump with engine off..inspected for leaks along the line and at fittings..nothing at all. Can I condemn the check valve at this point..or is there something else to possibly check? Fortunately, I did not put everything back yet in the rear..so pulling tank again to put another pump in is not a big deal..but sucks either way. Thanks everyone!!

Vader

It is possible that sediment in the tank has fouled the new check valve disc, and that running it for a period of time may clear it out sufficiently to hold pressure better. Another new pump may not fare any better unless the tank is surgically cleaned before everything is reassembled. The turbines of the pump can tolerate a little sediment, whereas the valve disc may not.

It is also not critical that the system hold pressure. The ECM runs the fuel pump for two seconds when the ignition is turned on, and does so specifically to build pressure for starting.

SbFormula

And it also runs as soon as cranking is activated right?

My Walbro never held pressure from day one, but builds pressure as soon as I crank.

IROCThe5.7L

Same here. When the pump primes, I'll lose all my fuel pressure in a minute or two. Car always fires in 1-2 cranks hot or cold. Even if I let the pressure fall to zero before cranking.

1989rocg92

Yes..it does prime and run..I just know in the 5 thirdgens I have owned since 1995, they have always held residual pressure. Speed density is a new experience for me though..Diacom was indicating over 9ms injector pulse (ambient temp just under 50F) width at initial cold idle and was running very rough until warmed up..I am used to the MAF 7165...perhaps the SD 7730 computer needed more time to learn. In any case, I was able to pick up a Delphi pump yesterday. When installing, I did give a thorough (as good as I possibly could) inspection of the inside of tank..not really any notable sediment. I installed the Delphi pump and it does hold residual pressure now...so either was check valve ...or was second guessing the tightness of the hose clamps from pump to sending unit. Fuel hose is pretty rigid..so I really made sure I tightened the snot out of those clamps this time...they seemed tight when I removed them though, but maybe not tight enough to hold the pressure?? Just guessing there...but I know they are very tight now. Anyhow..took for a test drive and everything seems to be running ok, initial start/run was not pig rich and BLM/INT numbers were within spec (122 - 128) in closed loop..so happy with that. Have one more question though..(maybe should post a new thread?) since Moates is closed, what is the go-to tuning software/hardware combo for OEM computer these days? TIA

SbFormula

Search TGO... lots of thread. Guy has an entire video on YouTube about it

https://www.thirdgen.org/forums/diy-...ernatives.html

That's one of them

1989rocg92

I'll check that out..thank you!!

Fast355

iTrader: (2)

Word to the wise, always replace the pulsator with a piece of immersion resistant, alcohol rated high pressure injection hose. Those things cause more problems than they solve.

ZorkRoc85

Hey 1989rocg92,

So a little history about myself here. I feel like its overdue. So ive been goshting the thirdgen form now since about 2009, without making an account or posting.. So many jobs I have accomplished because of the great info everyone has given on these forms. So heres my thanks as well as my own oppinion..
so I use the bluetooth adapter from RedDevilRiver.com, for datalogging my 85 iroc. Not many tuning options for my ECM, as my Iroc is mainly all from the factory parts, at around 78,000 original miles. No need for fancy chip tunning equipment unless your going to be burning chips. I have an old autoprom i usto use with my laptop. But that was years ago before I found out you really cannot change anything with my 6870 ecm, unless I convert my ecm.. however most of you guys on this form have the newer version ecms as opposed the 85 iroc-z's.. they are very rare these days and arguably junk. Doesnt bother me any. Heres the link for reddevilriver btw and i run this with ALDLdroid without too many issues. Win-aldl and a laptop may be an easier option for many though. https://reddevilriver.com/home-page/...scan-bluetooth

Also I need to pull my pulsator off as well and replace with proper fuel line as im finally starting to have the symptom of hard starts again. Key West is a bitch of an area to own a thirdgen. Freaking humidity truely ruins all.. but im the only thirdgen in the keys baby! driving around in my Nana's pre-ordered 1985 Iroc-z 305 tpi LB9!

All I can suggest is that you regularliy check your grounds and make certain all wiring is ship shape before trying to diagnose anything any further. And use sil-glyde on basically all rubber hoses/heater hoses/vacuum hoses.. other than my 2 cents, thanks for the info about the pulsators! The FPR is so easy to replace and should really probably be checked every year or so.. mine usto build up corrosion. I ended up putting a fuel rail from a 85 corvette in my iroc-z, everything was nearly a direct swap, except for a soft fuel line i had to run behind my holley throttle body.. as opposed to the hardline that normally connects that section on the 85's. Anyways my point was that if youv'e never really pulled your FPR, you should def do that. They're still pretty cheap these days, but common its 2023, and my beast still runs like a champ..

1989rocg92

Not sure how I missed this post...long overdue..thanks, I appreciate the info!! I have changed my FPR and diaphragm (TPIS adjustable). Another pump failure brought me back to inspecting this post (uugghhh!!). This one last over a year though, not like the initial failure I had with the Delco pump. I must say, the Delphi pump was super quiet compared to the Delco..on top of actually being able to hold residual pressure. The issue just started yesterday, barely made it home, as the car kept stalling. I would hit flat spots (fuel dropping out)..feathering the throttle a bit would help, but was stalling consistently at stops. So when I finally got home (I was so happy it just didn't totally die!!!), I unplugged the relay and placed a jumper on the harness to run the pump with engine off, got my meter out to check. Probed power/ground..resting voltage at battery was a robust 12.6.....with pump running on the relay jumper it was 12.3 (will drop under load, and car not running/charging) and 12.1 at the sending unit (after bulk head connector). Seems normal to me considering the length of the wire and under load, but I am going to jump out the bulk head connector just as a precaution (maybe I will just solder the wires..maybe a new 3-way connector..haven't decided yet). Pump would run sounding normal for about 5-7 seconds, then make this horrible noise (like a loud gurgling sound)..then stop just for a second, then repeat. So are all these pumps really built like crap? I hear good things about the Walbro, but also hear that they are loud..which I am not crazy about. Thing is..I have had five of these cars since 1994..and when I would replace a pump..I NEVER had to change it after. Last one I did lasted over 15 years, and far as I know (sold in 2018) it's still going! Any suggestions on a good reliable and quiet pump?

ZorkRoc85

Hey bro, not sure exactly about the pump. As in previous years my pump was only lasting a few years as well and did that gurgly thing you're describing. I was driving in Miami last year and my car died. Though it was a fuel pump issue and ran all over town trying to find a new pump and strainer. Got back to my car installed the new pump ( I have an access hole in my trunk to be able to swap pumps out quickly with compression fittings on my fuel lines. so any of that I figured could be an issue.) however once I pulled my pump out I realized I just ran out of gas and my gas gauge was messed up a bit.. lol but hey lesson learned there. I ended up getting home to Key West, and I pulled my pump out again from my trunk and sucked all of my old fuel out of the tank . It was full of dirt and debris from years of not cleaning it. I even dumped some of that 92% rubbing alcohol in there and went to town with multiple microfiber rags, as far as I could reach from the back of my car. Anyways I realized I had and issue as well were my fuel pump strainer looked like it was shaking loose and falling into the tank, I pulled out bits of plastic fibers all over my tank when I was cleaning it. Since I did that and installed a new FPR, my car runs like a gem now. I had a few wire gremlins going on (from mice or rats) that attributed to my gauge issues, but all in all that cleaning of my gas tank really helped me out more than I initially thought it would. So yeah maybe you're dealing with a similar issue with gunk clogging things up? Worth a shot, unless you gotta drop your rear end to access the pump.. even then it might be worth having a look see inside your tank.. Good luck man!

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1989rocg92

I have an access panel as well (courtesy of the previous owner ..I dropped the tank on my other cars)...but it sure does make it easier to get in and out..no doubt about that! Anyhow..I did a clean out prior to installing the crappy Delco pump last year, as I did see some sediment in the plastic tray..I got out as much as I could. If that damn plastic tray wasn't in there, probably could have done a better job though. When I pulled the pump last night, I did see some sediment in there..but nothing crazy. Going to clean it out again..but do you have any suggestions/methods to get a more thorough cleaning? (especially with that tray blocking view of tank bottom)

ZorkRoc85

Nice about the access plate! And yeah it's kinda a pain to get the right angle I was able to reach behind that plastic tray at the bottom your talking about towards the rear of the tank, I think I even used one of those "interior window extender handle things" with the triangle looking pads. But honestly I don't remember if that worked or not. I have some pretty long arms and was able to somehow get my body in a weird position to clean out most of that strainer bits that were everywhere. Also I used one of those hand pumps from like home Depot or whatever to make sure the tank was dry and after I cleaned it with rubbing alcohol I remember letting it sit for a few hours to dry out some more. Not that that part really matters. I use about a quarter of a bottle of high percentage rubbing alcohol in my fuel maybe once every year to make sure I'm burning off any access water in my gasoline. Not sure if any of that helps, but let me know how things go.