I have a 1987 chevy silverado 20 454 tbi with a turbo 400 with 72,000 original miles


Asked by Jul 12, 2013 at 07:19 PM about the 1987 Chevrolet C/K 20

Question type: Maintenance & Repair

I have a 1978 Silverado 3/4 ton long bed pickup with a TBI 454 and a turbo 400. the truck has 72,000 miles on it. it broke down on my daughter so I picked it up and replaced the fuel filter and some bad injector pigtails that needed to be replaced. the ignition module ended up being the problem after I put It in the truck started fine. I took it out to the store about 3 miles away with no problem, on the way back it acted like it was bogging down. I started testing it and it looses all power unless it is at an idle and out of gear. But even there if I rev the engine a few times I can get it to bog down. It just sounds like it is out of gas. note that it does not miss or backfire it just bogs way down.
It does not show any codes. I replaced both fuel pumps and socks last year and have around 14 psi when I test the pressure. i replaced the fuel regulator with a new on on the TBI I have tested the map sensor with a meter and vacuum pump and it checks out, I tested the TPS sensor, I vacuumed the EGR open and verified it was closing. I disconnected each vacuum line and pumped it down and watched for leaking. I verified that is did not have any broken grounds. since i live in the AZ Deseret rust is not an issue.  I inspected all of my lines for Pcv and brake vacuum lines for cracks. I Replaced the ignition module with two other to make sure that was not the problem. I replaced the pickup coil in the distributor. I have a very strong cone shaped stream from both injectors even when it is bogging down. I reset the timing after I pulled to distributor making sure it was up to temp and that I had the connector disconnected to the timing then disconnected the battery and connected the timing connector back up and then the battery, I left the battery disconnected all night to make sure there was not residual voltage anywhere. any thoughts.

9 Answers

...yes the fuel pressure regulator (the one that opens up when vacuum is applied) isn't supplying enough fuel...perhaps the diaphragm is torn and actually got sucked into the engine through the vacuum, perhaps the vacuum is the oie' butyl rubber (cheap) and cracked, a breach in the vacuum causing both high idle and stunted performance (due to low fuel pressure)~ recommend silicone hoses that will never crack or break~

2 of 2 people found this helpful.

this regulator would NEVER appear on your onboard diagnostics OBD-II, because it is not related to the computer (except fuel pressure....where this is where it all happens.

1 of 1 people found this helpful.

I am sorry but as i said in my original question. I replaced the regulator, with a new one on the TBI the original one was in very good shape but since i had it open i replaced it. but thanks for the reply.

1 of 1 people found this helpful.

I realized i said 1978 it is a 1987.

get a tune-up.


14 PSI on a fuel injected application seems low to me. I'd expect around 30 PSI. -Jim

1 of 1 people found this helpful.

TBI from that year were 9 to 13. But ruled fuel out yesterday. I was able to bog it down while it was in park by revving the engine and got it to bog and when did that i sprayed extra fuel into the TBI and the RPM did not increase at all. So i believe it now needs to be more of a ignition, timing, exhaust issue.

1 of 1 people found this helpful.

Exhaust and timing issues will usually cause the engine to run hot. Perhaps the catalytic converter is restricted. Make sure the bolt that secures the distributor is tight too. If you can move the distributor by hand it's loosened up on you. HTH. - Jim

your symptoms point to a throttle position sensor~

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