Carpokes

It was 97 degrees here today, so I took the 951 to the store to see if the pump would get loud. It did not, but presumably only because I only went 10 miles or so. I may go for a longer drive tomorrow if it stays hot, just to see... Getting toward the top of my 951 list is to try re-routing the fuel lines under the hood and/or adding some heat protection where the hoses run over the headers...

Stupid question but in what condition is the foam on the lower side your rear carpet?
I can hear the pump running only when driving without the rear carpet.

While the noise is annoying, it's a symptom of fuel pump suction cavitation. The more critical symptom is low fuel pressure as the pump is trying to push vapor rather than liquid through the system. Do you monitor fuel pressure? In turbo and kompressor cars, low fuel pressure means instant lean condition. That's quickly fatal under load and especially under positive manifold pressure. I'd be loath to add matting or carpet that might hide the telltale screaming noise that presages rod bearing and piston noises.

Disclaimer: I have zero direct 951 experience. I did have a high-boost CIS Saab 900 with a Bob-built engine/injection controller, so there's a tiny bit of 4-cylinder turbo experience behind my "suggestions".

Thom -- when I did the rear seat delete in this car, I learned the hard way how much the factory rear seat deadened the sound coming from the transaxle. I could hear the oil drip off the gears (almost) and it would whir like crazy at speed. So, I ended up doing dynamat in the seat well and rear deck. The factory sound mat is on top of that. Together, that got me back to nearly-stock gear noise level (along with a softer tranny mount filler). That said, when the pump starts to make noise, it's louder than anything you might sound deaden. From the outside, it sounds like someone put a seatbelt buzzer on a PA system....

dr bob -- the Saab 900 turbo and 951 have a ton in common in terms of engine/turbo management. Not sure there is another car more like the 951 in that way.... I do not monitor fuel pressure, but do monitor knock and air-fuel ratio, and would know on the spot if the car were going lean. So far, it's not. That's not to say the pressure isn't dropping on the other side of the regulator, but I'm pretty sure it's delivering at least the needed 3 bar even when screaming (so far). Tomorrow I'll spend a little time looking for a gas-submersible temp sensor. I'm not too proud to drop in down where you put the gas in. If hot fuel is causing this, it will be nice to have some empirical data to know if any of my gas-cooling ideas are working.

Tom, a simple type-k thermocouple-on-a-wire is fine for that. You can also test the metal nipple where the return hose enters the tank. The temp of that returning fuel is pretty much the temp of the fuel in the tank after it's been running a short while. No wires into fuel, no mess, everything already inside the cabin. Many decent DMM's have a thermocouple temp probe you can stick to the tube for a continuous reading, or use your IR gun immediately on stop but before you stop the engine if you need instant and effortless gratification...

dr bob wrote: Wed Sep 01, 2021 2:52 pm Tom, a simple type-k thermocouple-on-a-wire is fine for that. You can also test the metal nipple where the return hose enters the tank. The temp of that returning fuel is pretty much the temp of the fuel in the tank after it's been running a short while. No wires into fuel, no mess, everything already inside the cabin. Many decent DMM's have a thermocouple temp probe you can stick to the tube for a continuous reading, or use your IR gun immediately on stop but before you stop the engine if you need instant and effortless gratification...

Yes, I found a few such sensors I had left over from heated 3D printer beds and was working on exactly that. Stay tuned. The IR gun would be way too easy. I need a digital gauge.

Have you looked at the screen filter inside the pump? I’ve had a few get fully coated and become very noisy after warmup? In my case it’s been a fine dust material from the tank in my truck. Need to add a filter myself ahead of the pump.

Welcome aboard Sid! I changed the tank screen when I put in the original 044 -- so that was something like 10 years ago. If I have to replace this pump, I'll change the screen as a while-your-in-there thing. I would "think" it would happen more regularly -- not based on temps -- if it were the screen. I'm getting a temp sensor set up now, so can confirm that it really is based on temps though. I'm also running E85, and have to wonder if those tanks are as well maintained and debris-free as normal gas pumps with 100 times the daily turn-over.... Hoping to do a little recon this weekend....

After toying with the idea of making a 3D-printed temp sensor mount, I found these clip-on pipe sensors at digikey. By pure luck the pipe is the right diameter. The sensor is spring mounted in the clip so it stays pressed against the pipe. It reads up to 100C which I sure hope will be plenty high enough. Will work on a little digital gauge for this soon, hopefully before the weather starts getting too much cooler....

Well I finally got back to dealing with the fuel pump today, as it's been getting louder and louder and my smog check is due. I decided to pull out the gas tank strainer, which meant I had to drain out the last few gallons of the E85 that was in the tank. The strainer didn't look horrible, but it did have a film of muck on it. It rubbed off easily with my fingers, but it's possible that film was impeding the flow. New strainer and filter are on their way. In the meantime, look at the E85 that came out of the tank!?! If I was panning for gold, this would be great, but not so much in the gas tank. Much of that crud are metal flakes, and only a small fraction of it sticks to a magnet. I assume the strainer keeps most of that out of the pump, but I'm perplexed where it's all coming from? The gas goes through the strainer at the bottom of the tank directly to the pump, then to the fuel filter, and then up to the fuel rail/injectors, and then back to the tank. So where in that process do metal flakes get created and find their way back to the tank? I'd guess it's the pump failing, but anything the pump spits out should be caught in the fuel filter I would think? Would hate to think it's coming from the E85 gas station? Will cut open the filter and pump tomorrow....