1990 fuel pressure & vac readings good/bad? - ZR-1 Net Registry Forums

biggiefl · 11-14-2017

OK....1990 stock ZR1 #451 Just put in 16 new injectors a few weeks ago(Bosch). Went through all the vac. lines and all seemed good but I did not pressure test while plenum off. Runs and idles great now. So......:

1) at idle I have 42psi pressure on fuel rail. With engine off it drops to like 39 and stays. Will hit under full throttle like 48psi but at around 4800-5k rpm it drops sharply to around 30psi.

2) Vacuum gauge run off the drivers side center vac line going into the plenum(between #3 & 5 cyl. Read 12nm or whatever at idle. Would drop close to 0 when throttle blipped and up close to 25 and settle down to 12 again, no 17-22 normal. Brand new gauge and might not be accurate(will test on another car)but steady at 12. I think I might need to use a manifold vac line, not plenum but read that was the place? Some say start by vac pump or vac line under ECM?

3) I have used cold and warm engine temp. and sprayed ether around the entire engine, no pick up in idle.....nuttin unless sprayed in the air filter. Sprayed around every line and pump....nuttin. Could be I need to be under throttle to check some of the secondary stuff.

I'm thinking fuel pump(s) or filters or both......thoughts?

I'm getting tired(literally my back) with messing with this and would appreciate any and all ideas.

I know the info. is here but if you can supply part/pump info. #,s from rock auto or just the car/model(96 454 suburban?) would be mucho helpful. I am getting close but not sure where to start. I think the 30psi at 5k is not good, some say 55psi. I have more than 210hp but nothing close to 375 if that helps. I can get over 6k but it is not screaming like it did.

PS...As per rec on Mark's site I put in new AC Delco RF-5 plugs at I think .35 gap. Was that incorrect? Again runs and idles awesome, just not full power. I've heard .42 instead of .50 is good....confused.

Thanks, Nick

11-14-2017	#1
biggiefl Join Date: Jul 2017 Location: Ellenton, FL Posts: 8	1990 fuel pressure & vac readings good/bad? OK....1990 stock ZR1 #451 Just put in 16 new injectors a few weeks ago(Bosch). Went through all the vac. lines and all seemed good but I did not pressure test while plenum off. Runs and idles great now. So......: 1) at idle I have 42psi pressure on fuel rail. With engine off it drops to like 39 and stays. Will hit under full throttle like 48psi but at around 4800-5k rpm it drops sharply to around 30psi. 2) Vacuum gauge run off the drivers side center vac line going into the plenum(between #3 & 5 cyl. Read 12nm or whatever at idle. Would drop close to 0 when throttle blipped and up close to 25 and settle down to 12 again, no 17-22 normal. Brand new gauge and might not be accurate(will test on another car)but steady at 12. I think I might need to use a manifold vac line, not plenum but read that was the place? Some say start by vac pump or vac line under ECM? 3) I have used cold and warm engine temp. and sprayed ether around the entire engine, no pick up in idle.....nuttin unless sprayed in the air filter. Sprayed around every line and pump....nuttin. Could be I need to be under throttle to check some of the secondary stuff. I'm thinking fuel pump(s) or filters or both......thoughts? I'm getting tired(literally my back) with messing with this and would appreciate any and all ideas. I know the info. is here but if you can supply part/pump info. #,s from rock auto or just the car/model(96 454 suburban?) would be mucho helpful. I am getting close but not sure where to start. I think the 30psi at 5k is not good, some say 55psi. I have more than 210hp but nothing close to 375 if that helps. I can get over 6k but it is not screaming like it did. PS...As per rec on Mark's site I put in new AC Delco RF-5 plugs at I think .35 gap. Was that incorrect? Again runs and idles awesome, just not full power. I've heard .42 instead of .50 is good....confused. Thanks, Nick Last edited by biggiefl; 11-14-2017 at 12:12 AM.