Surge and ping

Hi,
My 91 2.5L has started all of a sudden to surge and ping at part throttle. I checked the EGR and at idle if I pull back on the diafram it starts to die out so that tells me it is not plugged up. Any ideas??
Thanks

It's probably time for a full tune up, then you should be set.

Don't forget to replace your fuel filter, since it'll help your very pricy to replace fuel pump live longer

Hi,
My 91 2.5L has started all of a sudden to surge and ping at part throttle. I checked the EGR and at idle if I pull back on the diafram it starts to die out so that tells me it is not plugged up. Any ideas??
Thanks

Unless you are a meticulous truck owner and/or perform preventive maintenance on a regular basis.....

If this were my truck, I would most definitely give it the full monty; the Tech IV (aka Iron Duke), while not the epitome of engine design and performance, is a lead pipe cinch to work on. A *FULL* tuneup, as OverBoard suggests is a great idea and you'll be surprised how much stronger your truck will run. If you don't have a Chiltons manual for your truck, now would be a good time to drop $20 on one. I would start with checking for any trouble codes.

Your '91 has probably well over 100K on it and the orignal EGR valve is probably not working to it's full potential; get a new one. Just because you can push up the diaphragm, causing the engine to stumble, does not mean it is working properly. Unlike early emissioned vehicles, a modern engine's performance is based on the EGR working correctly and you will actually decrease performance by having one malfunction or disconnecting it. The valve typically operates when the engine is at normal operating temps and a load is placed on the engine; the amount of recirculated exhaust gas being dependent on how much load (sensed by vacuum) the engine is under and the condition of the valve. They aren't expensive and relatively easy to replace. Also easy and relatively inexpensive is the O2 sensor located in the exhaust manifold; swap it out. It may be working just fine now, but if it's original you're on borrowed time. I would replace *ALL* the filters and breathers. Check any rubber vacuum lines, elbow fittings, etc for leaks and deterioration; replace any that look questionable. This engine still has a distributor (nastily located under the intake manifold and accessible through the right wheel well... a true PITA) and requires a cap and rotor; replace them as well as the plugs and wires. Also check the initial timing: set it to specs as per the underhood decal. Don't be tempted to "hot rod" it by setting the initial advance greater that spec; the timing is controlled by the ESC (electronic spark control, aka a computer) and it uses the base timing as a reference for advance and retard functions. The computer adage, garbage in garbage out applies here.

Also included in all this is a cleaning of the throttle body injector. Get a can of Gumout Carb cleaner and get the TBI squeaky clean. You can take your truck to a shop or try using some Chevron Techron injector cleaner (the stuff works but runs $6-9 a bottle) to scrub the inner workings of the injector. Put a double dose of Techron in and run your truck... if it begins to help, give it another double dose and then fill the tank with a normal dose of Techron.

Hopefully all this time and money will fix your problem. If not, then you'll have to dig deeper....maybe a partially plugged cat is adding to your woes.

An easy, *free* way to get a little more "go" out of "the Duke" is to gut the intake restriction at the very end of the plastic intake snorkle. You'll find a flared tube inside the snorkle, placed there to tame the intake roar of the big 4. A utility knife will make short work of the plastic welds and you can pop this inner baffle free. Once done, you *will* notice a bit more go and a bunch more "roar" from the intake...but it sounds kinda cool so that has to factor into it.

Learn, have fun and good luck,

Mike

P.S. There is a website/Forum for the Tech IV / Iron Duke engine and is another place you can go for info.... I don't have the address (computer crashed) but use a search of GM Tech IV or Iron Duke and you should find it...

Thanks for the reply Mike,
I did a full tune up on this truck about 5,000 miles ago (plugs, wires, cap/rotor, filters etc.) and it was running good until last week when this stumble/ping started. The truck has 65,000 on it in total. I took a shot and changed the TPS- same surge/ping. You are probobly right about the EGR being the next likely culprit on the list. Also the computer has not set any codes.
Thanks again
John

Surge and a ping sounds like its running lean on the fuel look for a vacuum leak also

Thanks for the reply Mike,
I did a full tune up on this truck about 5,000 miles ago (plugs, wires, cap/rotor, filters etc.) and it was running good until last week when this stumble/ping started. The truck has 65,000 on it in total. I took a shot and changed the TPS- same surge/ping. You are probobly right about the EGR being the next likely culprit on the list. Also the computer has not set any codes.
Thanks again
John

Did you replace the fuel filter?

What plugs are you using? Are they the right ones? Are they gapped properly?

I am using the correct Champian plugs. Also the fuel filter was changd about 5K ago when the tune was done. This problem happened all of a sudden. After the tune up was done 5K ago all was running good until one day last week.
Thanks
john

Hmmm....

Might try a different brand of fuel.