1993 Chevrolet Truck


First Chevy Truck

February, 7, 2011 AT 4:32 AM

My 93 Chevy C1500 4.3-Z) is very sluggish when accelerating, and shifts hard from one gear to another. It doesn’t run rough (neither cold nor hot) and does not surge, backfire or “ping”. No blue, white or black smoke from the exhaust. The lock-up converter kicks in at about 50 mph, but the truck seems to struggle more when I try to keep a constant speed between 40 and 45 mph either before the lock-up kicks in or when I drop it back to 40-45 after locking up. I can get it to run at 65-70 mph on the highway but I have to keep good pressure on the pedal as it seems to be working hard at that speed. When I disconnect the EGR valve and plug the vacuum line from the solenoid it runs perfectly and shifts very smoothly, just like a new truck, but the SES comes on after driving a few miles at 55+ mph. It goes out when idling for a few minutes at a red light.
I have replaced the plugs, distr. Cap, rotor, ignition coil, O2 sensor, spark plug wires, gas filter, cat converter (whole new exhaust system).
I enjoy tinkering with minor mechanical repairs, but what should I try first? The EGR?… EGR solenoid?… MAP sensor?… Any suggestions, other that bringing it to a shop for a diagnostic check? Thanks for your advice… anyone?


7 Answers



February, 7, 2011 AT 5:03 AM

Symptoms indicates a likely fault with the EGR system as the operating vehicle speed is within engine rpm range of between 2000 to 3000 rpm and disabling the EGR seems to resolve the problem, I would suggst starting from there.

Try cleaning the EGR solenoids and clearing the ports of clogging and retest. Carb cleaner is a reliable solvent for cleaning clogged ports, with the aid of a stiff wire.

If the SES light indicates intermittently, retrieving the trouble code would help to diagnose the problem.

The Assembly Line Data Link (ALDL) connector may also be referred to as the Data Link Connector (DLC) in flow charts. This is the same connector.

1. Turn ignition on with engine off. Malfunction Indicator Light (MIL) should glow. Locate Data Link Connector (DLC), attached to ECM wiring harness. Most DLCs are located under dash on driver's side of vehicle. Turn ignition on. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. See Fig. 1.

Inserting jumper wire into test and ground terminals of DLC with engine running will cause fuel-injected vehicles to enter field service mode and codes will not flash.

2. Malfunction Indicator Light (MIL) should flash codes. Each code is flashed 3 times. If codes DO NOT flash, perform DIAGNOSTIC CIRCUIT CHECK (GASOLINE). To exit diagnostic mode, turn ignition off and remove jumper wire from DLC.

Trouble codes retrieved from ECM/PCM/VCM may be related to either engine or transmission.

The ECM stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting Malfunction Indicator Light (MIL) flashes or with diagnostic scan tester connected to the Data Link Connector (DLC). The tester is faster, and capable of reading information which would require testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter.

When using a scan tester, there is a time delay between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, MIL flashes can be read by grounding DLC terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as DLC is grounded.

Trouble codes will be recorded at various operating times. Some codes require sensor or switch operation for 5 seconds and others may require longer under certain conditions. Some codes may not set in a service bay operational mode.

The above link should be helpful.

Let me know what you find.


First Chevy Truck

February, 8, 2011 AT 4:14 AM

OK. When the EGR is disconnected and the EGR vac solenoid tube plugged, the truck runs perfectly, but the SES light comes on at 55+ after about 5 minutes then goes out if permitted to idle for a few minutes. I stopped when the light came on, then checked the code. It gave me code 32. No surprise as the EGR was disconnected!

When the EGR is connected, the truck is very sluggish and the SES light does NOT come on. I checked if there were any OBD codes anyways. No codes. Go figure!

Do you still think the fault is with the EGR if there are no fault codes when it is connected?



February, 8, 2011 AT 12:37 PM

The EGR electrical system is working correctly thus no codes are present. The mechanical part of it could be at fault and when there is any leakage or clogging of the ports of the EGR system, it can cause the engine to sttuter thus the sluggish performance.

Remove the EGR valve and inspect the ports under it for clogging, mostly due to carbon deposits. Check the EGR valve for carbon deposits and clen it if necessary.


First Chevy Truck

February, 9, 2011 AT 2:32 AM

I notice there is a vacuum connector coming up out of the intake manifold near the front on the passenger side. This connector seems to be treaded into the manifold. It has 2 outlets. One is going to the vacuum accumulator (ball) and the other has been plugged with a screw. Where should that plugged one be connected? Could this be the source of the problem? I bought this truck from the son of the owner who passed away, so there is no way of getting the history.



February, 9, 2011 AT 1:15 PM

There are various vacuum diagrams and I have included all that are applicable.

I am not sure which outlet you are refering to. Hope the diagrams are helpful.


First Chevy Truck

February, 11, 2011 AT 4:13 AM

The 3rd diagram best represents my vac setup, but none show the Vacuum accumulator (4" diameter plastic ball). The outlet I was referring to has one lead to this "ball" and the other lead has been plugged.

Thanks very much for all your time. I'll take your earlier advice and clean ou the EGR port. Hopefully that'll do it.



February, 11, 2011 AT 1:37 PM

Sorry I could not find any diagram with an accumulator.

Hope the cleaning works.

Good luck.

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