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92 Cadillac Deville 4.9 Intermediate surge issues when accelerating

5K views 14 replies 6 participants last post by  ibdilbert 
#1 ·
Purchased this car back in mid February with just a little over 80 thousand miles on it. Car ran great until about three weeks ago. It started running rough at idle, and I noticed sometimes when you get into the throttle to pass it would surge until you let off the gas a little. Diagnostics said E41, so I replaced the pickup module in the distributor and the car today ran amazingly smooth on my way to work, about a 70 mile commute. On my way home, the surge came back, but this time worse than normal. If I accelerated above 50 it would surge badly, so I started to limp it home. About a mile from the house I couldn't keep it above 10mph, then it stalled and quit running. I turned the key, restarted the car and for maybe a mile, it ran like there was no issues, then did it again. While it was running badly, I put the car in diagnostic mode while driving and it gave me an E70 error. But now that its sitting in the driveway, I have no errors. E70 is TPS, does this sound like something that would cause all the above?

After the car sat for a while, I went out and pulled the line off the fuel filter and let the pump push fuel through the filter and into a gas jug, it pumps really good, so it may not be the fuel pump.
I took it another ride, and it ran great for about 7 or 8 miles, then started surging again when I got aggressive on the gas. I've also loosened the gas cap with no luck on the issue.

By surge, when I get aggressive on the gas pedal it feels like I'm pumping the pedal, or maybe the gas is start/stooping for half a second. Almost jerky like. Any ideas?
 
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#5 ·
Took it for another test ride tonight with an ODB scanner in live mode. Watched the TPS readings. Seemed to be .72 to 4.89 volts on the range, no fluctuations during the studder. Still has me puzzled, will look into some way to measure fuel pressure while driving, that might be kinda hard to do. the ODB only registers fuel pump volts, they stayed at 12.9 volts.
 
#6 ·
All you need is a fuel pressure gauge with a long enough hose to tape to the windshield. Most seem to come with short hoses. I spliced a piece into mine to lengthen it. The other option is to replace it with an old R12 refrigerant gauge hose. The fittings are the same, it just screws on.
 
#7 ·
Ok, today I stuck a fuel pressure gauge on it, was able to tape it to the windshield. When getting on the accelerator under load at higher speeds, the fuel pressure drops to 10 and in a few cases 7, at which it would studder.

Possible bad fuel pump? I've replaced the fuel filter, and have a good visual on all the fuel lines, no kinks or leaks. The fuel pressure regulator is not leaking gas into its vacuum port, or at least that I can tell. Removing the vacuum line from the regulator causes the pressure at idle to raise about 10 psi, so I assume the regulator is ok?
 
#11 ·
Dropped the fuel tank and pulled out the fuel pump. Inside the tank I can see the plastic baffles have broken into many pieces and are just floating around. Also I see tons of rust laying in the bottom of the tank. So I ordered a new pump, new gas tank and another new filter. All should arrive Friday, hopefully I can drive it again with confidence.
 
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