Hey guys, I have another stumper. 2000 Buick LeSabre 3800 surges when warm.

I've got a problem with my 2000 LeSabre I'd like to run by you guys.

It's got 189,000 on it and has had the MAF and coil pack changed in the past due to it quitting on me twice in the last eight years. When the MAF went out about two years ago I put plugs and wires on it too and it's been great since, until last Friday. I drove it to work, drove it to lunch, it ran great. I started it to go home that day and it was bucking and surging and wouldn't stay running. I finally got it home but had to drive it in 3rd gear otherwise it would stall. I stopped at AutoZone and had them check the computer and it returned a P0420, P0422 and P1133. He said it was most likely the first O2 sensor. I got one and decided to swap a bunch of parts from a wrecked 2000 LeSabre that runs great before I wasted the sixty bucks on an O2 sensor I might not need. The PCV valve was horrible so I pulled it and started the car and it seemed to run a lot better so I replaced it with a kit, not just the PCV. I pulled the crank sensor plug and it wouldn't start at all so I'm guessing it's good.

I swapped the following parts from the other car:

IAC
MAF (cleaned both with MAF cleaner)
MAP
TPS

I installed the new O2 sensor and now the car runs great until it warms up, then it surges up and down three or four times and then dies.

No codes with a tester at this point. WTH???

I'm really stumped and I need this car for work.

 

If you can get a fancy scanner see if you can read the coolant and air temps the ECU is seeing. Another thought is a dirty EGR.

 

Oh, I forgot that. I also swapped the EGRs.

 

Why would the fuel pressure only vary after it's warmed up? What about temp control sensors?

 

I don't know why it wouldn't, that's why I'm asking.

Yes, I wish I could just haul it to the dealer and have them put their ten thousand dollar machine on it but I can't afford to do that right now. I have known good parts on the other engine and very little money to work with. All I have into it at the moment is a $60 O2 sensor and $12 PCV kit, both of which it needed. Something else is still not right. That's the only problem with these cars, when they break it's expensive!

 

Wife's 3.4 Impala was acting goofy a while back.
Fuel pressure regulator was leaking past the diaphragm, and excess fuel was getting sucked into the intake causing surging and stalling. Pulled the vacuum line off the pres reg., and you could see fuel oozing out. Worth checking out.

 

I just ordered a scanner from Amazon that does a graphical readout of a bunch of things on a laptop or Android phone.

I keep going back to it being temperature related since it runs good now until it warms up. Once the thermostat opens up and I can feel heat in the hoses it starts surging. When I let it cool off even for ten or so minutes it runs fine again until it kicks the heat up.

I'm thinking out loud here, trying to take it all in and diagnose based on the components. The regulator or fuel pump seems unlikely because they aren't connected to the engine and in my mind it almost has to be a coolant temperature sensor but I don't know how they relate to the fuel system. The ignition module doesn't seem likely either because that controls spark, not fuel and it's away from the engine. I'm betting something on or in the engine is warming up and causing the issue. This can't be so hard to figure out, it has to have happened to thousands of these cars over the years.

 

I think the ones that will give the sensor read outs, not just the codes, are under $200 now. I agree, check fuel pressure and sensor readings. I usually do the sensor readings first, but the point is to do both. It could be a flaky TPS sensor causing accel enrichments and de-accel fuel cuts, could be a temp sensor shorting out causing the engine temp readings to swing from -40*F to 240*F, which really swings the fuel delivery and timing around, etc.

 

So while your swapping parts off the wrecked 2000 LeSabre... grab the coolant temp sensor.

Coolant temp, map and TPS are by far the biggest inputs to that system.

JW

---------- Post added at 09:27 PM ---------- Previous post was at 09:26 PM ----------

So while your swapping parts off the wrecked 2000 LeSabre... grab the coolant temp sensor.

Coolant temp, map and TPS are by far the biggest inputs to that system for calibration, and of course it has to have fuel pressure.

JW

 

Always verify good fuel pressure. you can buy a rent a gauge from the auto store. start there. the regulators fail on those. its not real common, but I've seen it a couple times. pinch the return line and take it for a rip.

 

Crankshaft position sensor can cause the symptons described. Have to test with a scope or replaced with known good.

 

X2 but you cannot always go by the pressure, you need to check flow also. The pump can still provide pressure but little to no flow which could be the surge.

I have also seen where a bad fuel pump "flow condition" cause erratic 02sensor codes. Customer would drive it and complain about WOT throttle when towing "GMC 1500" and have lean codes, clear the codes and have the same concern and then have rich codes. Fuel pump had good pressure and seemed to have good flow but we opted to replace the pump anyway. Concern was gone, no more codes and the engine picked up another 1k rpm under load.

 

The mother-in-law's '98 Park Ave had a similar problem-- would nearl stall, then rev up, would swing back and forth. It was a vacuum leak in the plastic tubing that runs from the throttle body intake across the front to-I think- the fuel pressure regulator? It had come apart at the rubber 'union'. Worth a look.
Patrick

 

You just spent alot of time rationalizing the problem and using "logic" to troubleshoot your problem. Try this for logic: You spent more time typing your rejection of a fuel pressure problem that it would take to put a guage on it. How foolish will you feel if it turns out to be a fuel issue? Just sayin', logic works both ways.

 

You can lead a horse to water...

 

Oh Shoot! Now I've done it! Now we won't ever find out what's wrong with it.

 

Go to the zone and borrow a fuel pressure gauge.

With the ignition switch ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gauge should be 333-376 kPa (48-55 psi). This pressure is controlled by the amount of pressure the spring inside the fuel pressure regulator can provide.
3.A fuel system that drops more than 5 psi in 10 minutes has a leak in one or more of the following areas:
The fuel pump check valve.

The fuel pump flex pipe.

The valve or valve seat within the fuel pressure regulator.

The fuel injector(s).

5.Fuel pressure that drops-off during acceleration, cruise or hard cornering may cause a lean condition. A lean condition can cause a loss of power, surging, or misfire. A lean condition can be diagnosed using a scan tool. If an extremely lean condition occurs, the oxygen sensor(s) will stop toggling. The oxygen sensor output voltage(s) will drop below 500 mV. Also, the fuel injector pulse width will increase.