Sat For 20 Years...Need Help With Diagnostic For Rough Running / Stalling (Page 4/6) CampyBob JAN 18, 08:29 PM Yesterday a 0-100 PSI gauge would not even hit the 10 PSI mark. Guessing/interpolating it was 7 to 8 PSI. No clue as to the resolution of the low end of that scale, but repeatability was good. I picked up what was 'supposed' to be a 0-15 PSI gauge from NAPA this morning. Despite the catalog describing the test set as 0-15 PSI it was actually a 0-10 PSI gauge. Bought it anyway and that pump I stuck in or the next replacement (if needed) better peg that gauge at 10 PSI+. Just a WAG, but my money is still on either a partially pinched rubber hose, crud getting sucked against the fuel pump sock or the pump is by-passing inside the tank. Possibly at the rubber hose that connects the pump output port to the steel riser line on the sending unit. So far the pressure relief valve has still not been seen to trip fuel into the tank return line. That is a screaming red flag to me that says, "Not enough pressure". Will have another go at it on Monday and report test result, but I can already see the tank coming down under that car again. Patrick JAN 18, 08:59 PM quote Originally posted by CampyBob: ... or the pump is by-passing inside the tank. Possibly at the rubber hose that connects the pump output port to the steel riser line on the sending unit. It was only a month ago that you had it all apart. What condition was the short length of hose at that time? Was it the proper submersible hose? Did you clamp it securely at both ends? CampyBob JAN 20, 08:42 AM Patrick, The OEM short length (2"?) hose was NOT clamped at either end and I did not clamp it when I replaced the pump. So, no, I did not add clamps there. WILL add clamps on the re-installation of the replacement pump or an exchange pump if this one fails to correctly pressure test when out of the vehicle and tank. The OEM hose was in good condition. Not soft. Good snug fit over both the fuel pump output port and the steel riser tubing. I re-used it. Other than a ton of 'crud' in the tank from the remnants of the gasoline the inside of the tank and sending unit was in darned good condition. Still, I'm guessing a bypass condition or more crud that I didn't get completely cleaned out of the tank fouling the strainer sock. Fuel at the inlet line to the inline filter is clean and clear. No crap coming out of the tank so if there still is some on the tank bottom it is not getting to the throttle body. Air temp is 14 degrees this morning! Too cold to do anything major today, but I hope to hook up my new 0-10 PSI gauge and turn the key to Run and see what I get. Any bets that pump does not peg the 10 PSI mark on the dial? Here's a pic of what was supposed to be a 15 PSI tester! David Hambleton JAN 20, 08:57 AM The Factory Service Manual suggests a flow test of 1/2 pint (236 ml) for 15 secs of pump action by grounding terminal G on the ALDL. Seems like a good test to run after the in-line filter. CampyBob JAN 20, 11:10 AM OK...definitive PSI reading. It's reading 2-1/2 PSI on the tank side of the disconnected inline filter line. That, to repeat, is 2.5 PSI. Weird that it is flowing so well, but obviously my 'fuel starvation' diagnosis causing the stumbling, rough running and lack of RPM's was correct. When the air temperature comes up the tank is coming DOWN! And Patrick, I lied...or let's just say old age and memory failed me! I DID remove the two old black plastic ratchet style clamps that were on the 2" hose and installed the two new black plastic factory ratchet clamps that came with the fuel pump and held the 2" long piece of hose in place. My apologies, sir! The old clamps were in great shape, clamped positively and I now remember removing them. Found them in the new pump box with the receipt that I stashed in the trunk compartment. So, I now doubt the pump is by-passing at the 2" hose area. Either the strainer sock is covered in filth, a line is partially pinched or plugged, the replacement pump is a piece of trash (doubt it ingested anything through the new strainer) or? This is the replacement pump I installed a few weeks ago: https://www.autozone.com/ex...1/563477_478947_6210 We'll soon find out! CampyBob JAN 20, 11:22 AM quote Originally posted by David Hambleton: The Factory Service Manual suggests a flow test of 1/2 pint (236 ml) for 15 secs of pump action by grounding terminal G on the ALDL. Seems like a good test to run after the in-line filter. David, Thank you! As a guess, I would say the flow rate is pretty close to that and why the engine was 'almost' running OK. I could flutter that gas pedal and get it to 3,500 RPM, but no way would it stay running. It was running itself out of fuel...definitely a starvation issue. The replacement pump is spec'd at a free flow rate of 49.9 GPH. or 1.65 pints per 15 seconds if I did the math correctly. With a minimum of 43.3 GPH flow rate that would be 1.44 pints per 15 seconds of run time. With a specified pressure range of 12 to 26 PSI it should be pegging my new 10 PSI gauge...but, sadly, it is not even close at a 2.5 PSI reading. Patrick JAN 20, 03:02 PM quote Originally posted by CampyBob: It's reading 2-1/2 PSI on the tank side of the disconnected inline filter line. Yep, no wonder the duke wasn't happy. It'll be interesting to (hopefully) discover what the actual problem turns out to be when you drop the tank. If it's any consolation Bob, I'm enjoying your thorough reports. CampyBob JAN 20, 03:21 PM Patrick, The only area I can think that I screwed up was in replacing the fuel pump outlet line that is about 5" long and is located in between the steel line coming out of the sending unit to the steel line that runs under the firewall area and heads up to the inline fuel filter. For some reason I cut the new piece of hose about 2" longer than the OEM one. Maybe to give me more wiggle to get it over the steel firewall line when I re-installed the tank? Well, it turned out to be a bad idea as the increased length did not have enough free space above it and it almost seemed to pinch the hose a bit. I played around with during the initial install and I 'think' I had it to the point there was no kinking or pinching in that hose, but now I want to double-check that. I think that would reduce the flow and before dropping the tank I'm going to try shortening the hose an inch or so. That's going to be a heck of a trick. Maybe pinch the hose off with Vice Grips if there's enough room and then cut the line to shorten it...all while holding a catch can while the line drains! Patrick JAN 20, 04:07 PM quote Originally posted by CampyBob: I think that would reduce the flow and before dropping the tank I'm going to try shortening the hose an inch or so. Definitely worth a try before dropping the tank again! CampyBob JAN 21, 12:23 PM Found the problem! It wasn't the pinched 5" external line. I did have that routed fine. But... I re-used the short OEM 2" long line that couples the sending unit to the fuel pump. It felt fine. Not soft or mushy and it was a snug fit over the steel line and onto the pump output port. Seemed legit... Unfortunately...when i put that initial 6 gallons of fresh gas in the tank it must have been enough to cover the 2" line that had been exposed to air for 20 years. THAT softened it up all right! It had a hole blown in the side of the hose! If anything will drop your fuel pressure to 2.5 PSI that would do it! It also explains why the car ran and revved perfectly when it was still on jack stands 5 minutes after the fresh gas was added. My guess is that in the following 24 hours or so before I tried that second startup and all the problems appeared was enough time for the new gasoline to attack the rubber and that next starting of the vehicle was when the 26 PSI fuel pump pressure blew the hole in the line and the internal by-passing started. Explains the pressure being so low the fuel pressure regulator and return line was not tripped and functioning. All this over a line I should have had the common sense to replace! LOL! The inside of the tank looked good. No real tons of crud or anything I was kind of expecting to find. I guess I did a better job of flushing it than I thought. The strainer sock looked good. I want to thank everyone for their help. Seriously, I appreciated every word of advice given! And the next time a guy comes into the forum asking what might be causing his rough running, failure to rev, stumbling condition after replacing the fuel pump you be sure and ask him to double-check the fuel pressure and make sure he changed out the 2" coupling line from the fuel pump! Tell him you know one idiot that did NOT!