5.2L knocking during hard acceleration

[chips2002]

Hi everyone, This is my first post. I have a problem with a 1991 B250 5.2L engine knocking during hard acceleration. I hope somebody could give me a hand with this problem.

This sympton does not really start up until the engine has been warmed up for about 20 minutes. I started to get this problem after I changed the head gaskets that were leaking and the pcv and breather filter grommets that were worn out. What I mean by knocking is that the carburator like chamber over the TBI (throttle body injection) starts to pop up and down and make this "pump pump" sound.

When I drive the car with the throttle pushed down about 1/4 of the way, the problem does not occur. But when pushed 1/2 way or more, the problem starts to occur. The other thing that I started to notice was that the van does not have a lot of power when going uphill. I floor the van on a 30 degree incline, and it is still losing power and slowing down. The van is pretty much empty inside except some minor tools I carry with me for work.

I tried to fix this problem by changing the fuel filter and put in 2 12 oz cans of Chevron Concentrate fuel infection cleaner with 20 gal of 91 octane gas. There still has not been any improvement. I am the first owner of this van and had it since 1991. Ever since i bought it, I only put in 87 octane gas. I have done all the tune ups I can think of (spark plugs -- standard heat range champion 404, cap, rotor, ignition wires, ignition coil, pcv, cleaned out breather filter, TBI cleaning, air filter, coolant, fuel filter). I also tried using Bosch platinum plugs instead of the Champion 404's but still have the same problem.

I have heard of other members having pinging and knocking problems due to there spark plugs. Could it be that I need colder type plugs or different brand plugs? Or could I have problems with my injectors?

I would appreciate it if anybody could give me advice with my problem. Thanks and sorry about the long write-up.

[1972roadrunner]

is it a preignition type of 'ping'? when you changed head gaskets, you didn't bump the distributor did you? do you have a timing light? you might wanna check the timing.

one thing, you might wanna post this on "performance talk", more people will be able to help you there.

[chips2002]

No I did not touch the distributor when changing the gaskets. The mark on the distributor is still lined up as before. I dont have timing gun right now so cant really do the adjustment. But as I was driving today, the knocking kind of felt like a backfire rather than a knocking. When looking back at my previous post about the "pump pump" noise I think it is a backfire, the TBI chamber moves up and down. Is this the same thing as knocking and pinging? I feel this surge when this happens the it seems like the engine is stalling when backfiring.

[1972roadrunner]

i'm not too familiar with mopar TBI...or really any TBI... my dads 93 chevy has it, but never been any problems...

i would definently put this under "performance talk"...you'll probably get more help there. not too awefully many people come to "power adders"....

good luck!

[gmblows]

How is the fuel pressure?
I saw a Magnum 5.2 van run the same way with a bad fuel pump.

[RRussell68]

Did you have the Dealer reset the Sync signal? If the noise sounds like a backfire soming through the throttle body, it is the sync signal off.