89 Silverado Sputtering on accelaration

[electro452]

I have a 89 chevy silverado with 380000 miles. It has the 5.7, 350 engine, 2 wheel drive , automatic. The past few days I've noticed when the engine is cold , the engine starts sputtering on acceleration. If I ease off the gas and let it accelerate slowly it seems to be okay. Once the engine is warms the problem is not present. I haven't checked anything as of yet but wanted to get some input so I'm not chasing and replacing things for no reason. I did a complete tune up about 7000 miles ago. Cap and rotor, plugs and wires, fuel filter and pvc valve, EGR valve, coil and fuel pump( only becasue my float has been sticking for years). Any suggestions would be apprecaited. I run the K&N air filter and I just cleaned it last month.

I did notice one item the past few months. When I open the passenger door after I get done driving I can smell gas. I thought it problably coming from the engine compartment air intake since it feeds from the passenger side.

[electro452]

Well I changed the fuel filter, distributor and rotor becasue they looked a little worn but not enough to cause a problem. But i had them off so i just slapped a new one on. I'm suspecting maybe a fouled plug since it run fine after it gets to operating temp. My only reservation with a plug issue is it's idling fine, only sputters when accelerating so i have to let my foot off the gas, like it's getting too much...

[j cAT]

Originally Posted by electro452

Well I changed the fuel filter, distributor and rotor because they looked a little worn but not enough to cause a problem. But i had them off so i just slapped a new one on. I'm suspecting maybe a fouled plug since it run fine after it gets to operating temp. My only reservation with a plug issue is it's idling fine, only sputters when accelerating so i have to let my foot off the gas, like it's getting too much...

replace the ECT and check for good wiring connector . if this is not working correctly the engine fuel control when cold can cause an improper mixture.

with a carb set up check the fuel vapor system for proper operation. these controlling vac lines and components fail causing a very rich mixture .

[electro452]

I'll give those items a try, thank you. I have the throttle body , how do you check fuel vapor system for proper operation?

[electro452]

. I checked the resistance on the engine coolant sensor, it seemed off by a few hundred ohms according to the chart I have in relationship to temp and resistance. So I replaced it but this did not resolve the issue.

[j cAT]

Originally Posted by electro452

. I checked the resistance on the engine coolant sensor, it seemed off by a few hundred ohms according to the chart I have in relationship to temp and resistance. So I replaced it but this did not resolve the issue.

with the ECT replaced then look at the throttle body injection . look into the top of the TB see how the fuel is coming out. both should look the same .should not be dripping fuel ..then you can also do the injector resistance test of the coil. make sure the volts to injectors is good and solid..return side is grounded to create voltage pulses these open the injector. using a light is good to see if the pulses are the same .

an example of the ect resistance is 4.5K OHMS 60 deg f....180 deg f about 200 OHMS. open circuit is -40 deg f.........

fuel vapor hose goes into the intake I believe under the TB. pull off that hose and see if you can get a strong smell of gas..look for the canister follow the vapor line to the engine ..pull off line check for fuel/strong gas smell..

[electro452]

Originally Posted by j cAT

fuel vapor hose goes into the intake I believe under the TB. pull off that hose and see if you can get a strong smell of gas..look for the canister follow the vapor line to the engine ..pull off line check for fuel/strong gas smell..

If I have a strong gas what does this indicate?

[j cAT]

Originally Posted by electro452

If I have a strong gas what does this indicate?

with the strong smell of fuel the canister has a control valve .this valve will develop a leak causing the vacuum to suck fuel from the tank into the intake. I would disconnect this line at the intake ..plug up the bore that it connected to on the intake ..then see if the engine runs good. if so then the valve or the complete canister may require replacing.

post back .. these 1980 vehicles had these type issues ..

[electro452]

I check the evap canister and it did not have a gas smell. I also checked to see is if it was plugged up buy it is clear. I did check the injectors for good cone shape on the spray pattern. I did notice I have a drip on both injectors, not bad but I'm wondering if it gets worse under load and the engine is cold and stops as it gets nice and warm. The TB has never been removed, cleaned and the regulator rebuilt so I'm thinking that should be done if nothing else just because it's 25 years old.

[electro452]

Well I finally got back to this issue. I had to take a break from it due to another issue with the 700R4 transmission that popped up all of a sudden. So another rebuilt trans latter I'm back to the original problem. Just to eliminate possibilities and since the issue mostly disappears once the engine gets to operating temperatures, I figured I would start with the electrical items again. So, I bought a good set of A/C Delco plugs, same as the original and what I was replacing, and a good set of plug wires instead of the Dura _ _ _ _ from Autozone that I was currently using. Replaced plugs and plug wires, started up engine nice and cold, let idle for 45 seconds and then punched it..... Baby purred like a tiger!!! No hesitation, no sputtering, no nothing, ran beautiful. So, even though the plugs and wires looked fine when removed and thy were only about 6 months old, one is bad. I suspect the plug wires. Serves me right for going away from the good brand and to the cheap brand.

Thank everyone for your help and input

[j cAT]

plug wires need be the correct resistance. every manufacturer has a resistance spec.

I have a LT1 engine and I have gone to the store looking to buy plug wires that claimed to be the exact fit for my LT1 ....WELL guess what ??? the resistance was 2-3X higher than the GM spec. I had to order the AC delco wires and these where the exact correct resistance. If I had used the higher resistance wires this would have damaged my ICM/OPTI distributor...

before installing any plug wires you need to check the resistance. with installing you must use the dielectric grease in the boot ends to protect the core wire from damage due to arcing..........good luck.

[electro452]

Good info J Cat.

I did use the dielectric grease on the boots.

I just came back from getting my 2 year smog and this is the first time it passed easily. Usually I'm right on the numbers.....

[j cAT]

Originally Posted by electro452

Good info J Cat.

I did use the dielectric grease on the boots.

I just came back from getting my 2 year smog and this is the first time it passed easily. Usually I'm right on the numbers.....

sounds good more MPG maybe ..