The problem ... and the FIX! Fuel or spark diagnosis
#1
12-21-2016, 10:38 PM
The problem ... and the FIX! Fuel or spark diagnosis
Figured I'd post this one up to maybe help someone else that runs across this one. I think you may have a better chance of winning the lottery, however! 
So, we've got a '95 Volvo 940 wagon, non-turbo. Complaint is, it fires up and runs great every morning, then at the first stop sign, it croaks, and won't restart the rest of the day, requiring a tow home. Guy who owned it dumped THOUSANDS into it chasing this problem. He gave up, and it sat for years.
So I get it here on my flatbed trailer, and proceed to verify the complaint. The thing idled without missing a beat for 45 minutes, so I jumped in to try and simulate driving. Held it at 3k for about a minute, then slammed the throttle shut. Immediately I could hear cylinders dropping out. Aha! I was convinced it was an ignition issue. Grabbed my timing light, and watched it flash all the way until the thing croaked. Hmmm ...
For the next test I grabbed my fuel pressure gauge, and put it on the shrader valve before the fuel filter under the car. ZERO psi! OK, now we're getting somewhere! Get in the car and turn the key - I can hear the pump running. Look at the gauge - 0 psi. WTF?? Now I'm wondering if my gauge, or the shrader valve is screwed up. Retightened the fitting - still zero. Decided to yank the fuel pump and see what was up.
Removed pump from the sender assembly, got a battery and connections ready, and put the pump in a jar full of acetone outside. Pump ran, not a drop came out! Tried hitting the ground clip on the negative a few times to rapidly stop/start the pump - when the pump ran, I heard a POP, and acetone shot 6' in the air. So, the problem was a faulty check valve in the fuel pump. It's only supposed to restrict flow TOWARDS the pump, not away from it. That was a new one for me! This ain't my first rodeo either - I see lots of fuel pumps each year.
Was a Walbro pump - saw it stamped on the pump case. Normally those are very well built pumps. Guess no brand is safe from poor manufacturing, or QC these days.
Owner ordered a new pump from Autopart International, they delivered it here, I installed it, and the car is back to running like a champ again.
Figured I'd share the saga. Enjoy!
So, we've got a '95 Volvo 940 wagon, non-turbo. Complaint is, it fires up and runs great every morning, then at the first stop sign, it croaks, and won't restart the rest of the day, requiring a tow home. Guy who owned it dumped THOUSANDS into it chasing this problem. He gave up, and it sat for years.
So I get it here on my flatbed trailer, and proceed to verify the complaint. The thing idled without missing a beat for 45 minutes, so I jumped in to try and simulate driving. Held it at 3k for about a minute, then slammed the throttle shut. Immediately I could hear cylinders dropping out. Aha! I was convinced it was an ignition issue. Grabbed my timing light, and watched it flash all the way until the thing croaked. Hmmm ...
For the next test I grabbed my fuel pressure gauge, and put it on the shrader valve before the fuel filter under the car. ZERO psi! OK, now we're getting somewhere! Get in the car and turn the key - I can hear the pump running. Look at the gauge - 0 psi. WTF?? Now I'm wondering if my gauge, or the shrader valve is screwed up. Retightened the fitting - still zero. Decided to yank the fuel pump and see what was up.
Removed pump from the sender assembly, got a battery and connections ready, and put the pump in a jar full of acetone outside. Pump ran, not a drop came out! Tried hitting the ground clip on the negative a few times to rapidly stop/start the pump - when the pump ran, I heard a POP, and acetone shot 6' in the air. So, the problem was a faulty check valve in the fuel pump. It's only supposed to restrict flow TOWARDS the pump, not away from it. That was a new one for me! This ain't my first rodeo either - I see lots of fuel pumps each year.
Was a Walbro pump - saw it stamped on the pump case. Normally those are very well built pumps. Guess no brand is safe from poor manufacturing, or QC these days.
Owner ordered a new pump from Autopart International, they delivered it here, I installed it, and the car is back to running like a champ again.
Figured I'd share the saga. Enjoy!
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