fuel pressure?

[swoop]

Where would I check the pressure from the regulator? The fuel pump pressure I can check at the inline filter connection right? But Im stumped at the regulator. I own an 89 suburban 5.7L TBI. I have a cold start issue. The burb will start after 4-5 turns then idle very rough and die, then restart and feather the accelerator untill it reaches idle. It has a very noticable miss every 5 seconds or so. Ive changed the fuel filter and could blow through the old one. Put a bottle of injector cleaner in along with a bottle of heet. Only code it has thrown was a 43. Which I believe is the electronic spark control circuit. The engine was pinging very badly when it did this is why I believe it is fuel related. Any help would appreciated.

[2000CAYukon]

The regulator is inside the TBI. If you check the fuel pressure at the fuel filter location (need a special tool to do this unfortuantely), then you are checking the pressure that is being regulated.

It is hard to see if the regulator is leaking or not. I recently rebuilt my TBI and used an AC Delco kit and it did not come with a regulator diaphram. The Borg-Warner rebuilt kit does come with the diaphram (wish I knew that before I opened the AC Delco kit).

There is one company that sells a regulator with a built in gauge but it is pricey. Here is a link to it http://www.cfm-tech.com/catalog/fuel...tbi_549435.htm Note that the price does not include the gauge.

Good Luck.

//2000CAYukon

[swoop]

Thank you, but I'm lost when you say that the fuel pressure at the inline filter location is regulated? Do you mean that it is regulated by the fuel pump pressure? It wouldn't be regulated by the fuel pressure regulator on the tbi would it? The filter location is in front of the fpr.

[FCDGMC]

I think what 2000CAYukon (correct me if I'm wrong) is saying is that at the fuel filter you are checking pressure that is later regulated by the fuel pressure regulator so you're not checking whether or not the FPR is functioning properly. I also have a TBI (albeit 7.4L) and the FPR is part of the injector body. I have also priced out this regulator and it's 126 for the 7.4L (which has two injectors-not sure if the 5.7 has one or two-that picture is hard to tell) so the adjustable/measurable one he's proposing might be a pretty good deal.

2000CAYukon-not clear to me, is the FPR the same for both the 5.7 and 7.4? Hard to tell from that picture if it has one injector or two. The website only appears to have products for the 5.7.

Thanks

[2000CAYukon]

Originally Posted by swoop

Thank you, but I'm lost when you say that the fuel pressure at the inline filter location is regulated? Do you mean that it is regulated by the fuel pump pressure? It wouldn't be regulated by the fuel pressure regulator on the tbi would it? The filter location is in front of the fpr.

The fuel pump is in tank. It pumps fuel thru the filter into one side of the TBI where the regulator is. It bleeds off pressure thru the return line to the tank. The return line is also connected to the regulator.

The fuel pressure you see at the filter is the pressure that the regulated by the fuel pressure regulator.

For TBI, if the pressure is over 15, then the regulator may not be doing it's job.

By the way, this is similar to newer GM trucks. The test port in the fuel rail will show you the regulated fuel pressure since the regulator controls what fuel is sent back to the tank via the return line.

Why they did not put a test port on TBI truck is a mystery to me.

//2000CAYukon

[2000CAYukon]

This article may help http://chevyhiperformance.com/techarticles/49279/

The difference for TBI is that the supply line and return line are connected directly to the TBI.

//2000CAYukon

[2000CAYukon]

Originally Posted by FCDGMC

I think what 2000CAYukon (correct me if I'm wrong) is saying is that at the fuel filter you are checking pressure that is later regulated by the fuel pressure regulator so you're not checking whether or not the FPR is functioning properly. I also have a TBI (albeit 7.4L) and the FPR is part of the injector body. I have also priced out this regulator and it's 126 for the 7.4L (which has two injectors-not sure if the 5.7 has one or two-that picture is hard to tell) so the adjustable/measurable one he's proposing might be a pretty good deal.

2000CAYukon-not clear to me, is the FPR the same for both the 5.7 and 7.4? Hard to tell from that picture if it has one injector or two. The website only appears to have products for the 5.7.

Thanks

It does look like the regulators are the same for the 5.7 and 7.4. The 5.7 does have 2 fuel injectors. Note that AC Delco only sells the complete regulator which is why you see it priced at 126. www.rockauto.com has it 78 plus shipping. You can however buy just the diaphram which is usually what wears out. I have found the diaphram and gasket locally for about 30 (see www.partsamerica.com).

There are a few companies making adjustable regulators. The one I listed previously could also take a gauge and was fairly expensive. If you are trying to squeeze as much hp out of the engine, an adjustable regulartor may be helpful, but I don't think it will be that much.

//2000CAYukon

[swoop]

Thank you, this sheds alot of light on the subject. The article you put in the thread was a good help as well. I plan on testing my fuel pressure as soon as possible. When I test the pressure, do I have to remove any vacume lines?

[2000CAYukon]

Originally Posted by swoop

Thank you, this sheds alot of light on the subject. The article you put in the thread was a good help as well. I plan on testing my fuel pressure as soon as possible. When I test the pressure, do I have to remove any vacume lines?

On our TBI trucks, the vacuum for the regulator is internal to the TBI unit itself so there is no vacuum line to remove. It is also difficult to test if the regulator is leaking since the vacuum port is internal.

On vehicles with the regulator on the fuel rail, the vacuum line can be removed to test the maximum fuel pressure (i.e. no vacuum simulates wide open throttle) and to see if fuel is leaking thru the diaphram (fuel in the vacuum hose indicates it is leaking).

9 - 13 PSI is the specs for TBI. Note that it is normal for the pressure to drop to 0 when the ignition is turned off. On newer vehicles with higher pressures, a drop in pressure when the ignition is turned off can indicate a bad regulator.

//2000CAYukon