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951 Surging

 
Old 03-13-2019, 05:48 PM
  #1  
BrianRMV
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After a long absence I have my 1986 951 back. On the drive back from the shop (35 miles +-) it ran very well. Traffic was busy, so there was minimal hard acceleration. The next morning I took it out and it seemed to run well until the last couple of miles. Under steady, low rpm, load I could feel a slight surge up and down. After a stop I gave it maybe 75% wot and it surged hard up and down. I let off on the accelerator and it seemed fine. The same has happened since, so I have parked it for now. I have reason to believe that it could be a TPS problem. My turbo is also leaking oil, and the impeller shaft is loose (pointed out to me by a mechanic). Can the turbo fail intermittently like that? It makes sense so me, but I'm not what anyone would call a mechanic. I am going to buy a rebuilt turbo regardless. I see Lindsey Racing has them available at what looks like a really good price.

Any thoughts or advice would be greatly appreciated.
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Old 03-14-2019, 11:16 AM
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mytrplseven
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How old is the gas in the car? This is sounding like a possible fuel delivery issue. I'd say borrow or buy a fuel gauge and do the Clark's Garage series of system tests. If you have really old gas, doing an injector spray test is in order. It only takes a 9v battery to energize each injector with the DME relay jumpered to check the spray into a plastic (preferably) container. A couple of wires (or small alligator clips) and tapping the injector connector pins will energize the injector long enough to see the spray pattern and see if the injector if working. When was the last time the fuel filter was changed? Water in the gas (I noticed you're in WA)?
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Old 03-14-2019, 01:49 PM
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BrianRMV
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The tank was nearly empty when I picked the car up so the gas is new. The fuel filter was changed within the last 4 or 5 years. The injectors were replaced about 2 years ago. It could be an issue with fuel delivery. The last mechanic who worked on it opened the TPS up. He said the pin that moves the potentiometer was not engaged. The casing is literally taped together now. It's interesting that it runs well for a while, then surges under heavy load. The mechanic I saw for the first time a few days ago adjusted the TPS and idle, and it ran really well during our test drive. When I was almost home (about 20 minutes away from the shop) I experienced the surge under fairly heavy throttle. Does a failing turbo ever behave like this? I'm guessing that if it was failing badly I would not need to ask.
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Old 03-16-2019, 04:40 PM
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I make it a habit to change the fuel filter every year. In your case, the tank was sitting almost empty and contaminants are more prone to settle and a fresh fuel fill can stir them up. I'd go with a new filter and see how it goes. After that, look at a complete fuel pressure test as it could also be Fuel Pressure Regulator (FPR) related. As it's vacuum controlled, check that line as well.
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