Maybe Somebody here can Help? (Chevrolet issues)

Topic: Maybe Somebody here can Help? (Chevrolet issues) (Read 1166 times) previous topic - next topic

Maybe Somebody here can Help? (Chevrolet issues)

July 02, 2014, 01:05:51 PM

While I'm waiting for my Thunderbird to get finished up at the shop, I've been working on the '89 C-1500 (350 cu in/700R4) I've had since '06.

Seems as though since January it's been running like garbage, at times.

So, after a new gas tank, new intake manifold gasket, EGR valve, new MAP sensor, new Throttle Positioning Sensor, new timing chain and gears, new distributor cap & rotor, new plugs and wires, new coil pack, new computer, and new fuel pressure regulator, the pick up still has the same hesitation from 1/2-throttle to 3/4-throttle it's had for a while, now...

There's no vacuum leaks on the engine and the compression is good on the 4 cylinders I've checked.

The sumbitch runs like a spotted ape aside of the hesitation, so it's got me confused as all get out.

I know it's hard to diagnose a vehicle behind a computer screen, but might anybody have anything to offer? I'm thinking new fuel pump. As far as I know it's got a new fuel filter, but I'll probably go ahead and replace that as well, if I replace the pump.

Maybe Somebody here can Help? (Chevrolet issues)

Reply #1 – July 02, 2014, 01:52:30 PM

Codes?

Maybe Somebody here can Help? (Chevrolet issues)

Reply #2 – July 02, 2014, 03:14:57 PM

Since I put in the new fuel pressure regulator it's not throwing any

Maybe Somebody here can Help? (Chevrolet issues)

Reply #3 – July 02, 2014, 04:44:13 PM

Do you have a known good oem map sensor?

I had a couple Saturn's and they would really act up with map sensors from parts stores
I would throw the old ~100-200k mile old sensors on and they ran awesome
Just something to look into

I would also to a resistance sweep test on the tps

Maybe Somebody here can Help? (Chevrolet issues)

Reply #4 – July 02, 2014, 05:17:52 PM

Pop your distributor cap off and check the rotor for excessive play (try turning it back and forth). Some play is normal, but if it's really sloppy you might have a worn distributor gear

Maybe Somebody here can Help? (Chevrolet issues)

Reply #5 – July 04, 2014, 02:20:58 PM

I put a new fuel filter on it (thought it had a new one, but I was mistaken), and it's cleared up the issue almost 90%. When I get right around 1/2 throttle it will hesitate a little bit, but runs like a champ anywhere else in the throttle.

TC, I had the distributor out when the timing chain was changed and it was in top notch shape.

Maybe the 302,8XX miles is finally catching up with it? But dang it, the truck runs too good.

Maybe Somebody here can Help? (Chevrolet issues)

Reply #6 – July 06, 2014, 04:57:13 AM

I think I have it narrowed down to the throttle body. When I get to half-throttle quickly, it sounds like there's a big rush of air. Not sure if it is some kind of vacuum leak around the throttle body somewhere, but I shall find out later today.