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Old 08-02-2011, 07:49 AM   #1
TopherBrowne
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Dizzy 98 SL2 - new EGR - problems when connected - no problems when disconnected

Greetings forum. My girlfriends 98 SL2 has a problem. When driving, after the engine has warmed up, there is sudden hesitation and then surging even when driving flat and at constant speed. It also was sounding like it wanted to shift to a higher gear but couldn't.

We went to a mechanic and he told us that the EGR valve was bad and that the wire conduit for the EGR wires had melted against the engine block.

After a little research, I decided I could do this repair. We got the new EGR valve, I installed it, and also spliced new wire replacing the portions that had melted and fused. The repair part was easy.

The same problem exists. If the EGR valve is connected, we get the SES light and the surging happens within minutes of a cold started engine. If the EGR valve is disconnected, the SES light comes on and the problem does not appear even after many miles.

I've done some searching and have come up with coolant sensor as a possible thing to look at. I am checking Chiltons now.

In the meanwhile, what's next? I'm not a mechanic but am mechanically inclined.

Topher Browne

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Old 08-02-2011, 10:06 AM   #2
td1238
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1999 SL2
Default Re: 98 SL2 - new EGR - problems when connected - no problems when disconnected

What does the SES light say? Did you have the codes read? Did you remove all of the bad part of the EGR valve harness? Did you connect the new one properly?

The new EGR valve is not likely at fault, but could possibly be. Have the codes read first. Autozone will do it for free.

The problem was happening when the engine was warm and now cold, so it is possible that you mixed up the wires.

Another thing that can cause surging and random shifting is a worn TPS, but have the codes read first.

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Old 08-03-2011, 09:23 AM   #3
TopherBrowne
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Default Re: 98 SL2 - new EGR - problems when connected - no problems when disconnected

Quote:
Originally Posted by td1238 View Post
What does the SES light say? Did you have the codes read? Did you remove all of the bad part of the EGR valve harness? Did you connect the new one properly?

The new EGR valve is not likely at fault, but could possibly be. Have the codes read first. Autozone will do it for free.

The problem was happening when the engine was warm and now cold, so it is possible that you mixed up the wires.

Another thing that can cause surging and random shifting is a worn TPS, but have the codes read first.
I don't have diagnostic tools and am relying on the information the mechanic provided. The car is the MBFI? version where the valve is cylindrical (not mushroom). The part swap was easy and very straight forward.

The wire connector to the valve is not damaged. The conduit of wires that melted was about 8 inches down from the actual connector. Two of the five cables were compromised. I removed the melted wire and spliced new wires with butt connectors. Same color wire to same color wire.

The problem is present when the new EGR valve is connected via the wire connector. When the connector is removed, the problem does not happen. This is also what was happening prior to replacing the EGR valve.

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Old 08-03-2011, 07:43 PM   #4
td1238
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Default Re: 98 SL2 - new EGR - problems when connected - no problems when disconnected

Others on here may be more knowledgeable of this problem, but I will help as I can.

First, go to AutoZone. Have them read you the codes. This will be most helpful.

Second, obtain an ohmmeter, preferrably with narrow insulated alligator clip leads. Unplug the TPS. Connect one meter lead to the center terminal of the TPS. Connect the other meter lead to one of the end terminals. Set meter to something like ohms x100. The meter should, preferrably be anolog, but digital will do. Select a scale that allows deflection of the meter through a good portion of its range. Operate the throttle slowly through its range and observe meter reading. Resistance should change smoothly, and should start and stop in the same place every time. Repeat for the other side terminal. If resistance jumps around replace the TPS.

A dirty or worn TPS is not likely to affect the EGR valve much, but does affect shifting on an automatic transmission, and can create jumpy shifting and driving. The EGR valve does, however, open on throttle position, among other things, and a bad TPS could possibly cause the EGR valve to slam open and shut.

Also, though the EGR valve is new, test it in the same way you tested the TPS. Connect to the center terminal, and to each of the terminals on the side of the center terminal. These all go to a position sensing device inside much like the TPS. If faulty, the EGR valve cannot be opened accurately by the computer. If opened too much, especially at small throttle openings, it can adversely affect combustion heavily. In my experience, however, extreme jerking or bucking did not occur.

Also make sure that the TPS, EGR valve, and MAP sensor plugs are well connected, and that the engine doesn't buck or stall when they are wiggled by hand.

You could also have fault connections in your splices to the EGR valve plug. Be sure that they are well made. Twisting of the engine as torque is applied to the wheels can vibrate these connections.

Another very remote possibility: reset the computer. Disconnect the negative battery cable and turn on the headlights. Leave it this way for 10 minutes to be sure that the computer's storage/filter capacitors have been completely drained. Usually this method resets the computer right away, but 10 minutes makes it sure.

Good luck!

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