GM TBI Fuel Pressure Problems

[Oldswagon]

I have a '93 Suburban with a 350 TBI engine and approx 170K miles. The truck runs well, except for during certain circumstances the engine will cut out. This generally happens at highway speed, when increasing the speed and load of the engine (not enough to cause a downshift). It feels like the engine is shutting off then coming back on but very quickly. Under most other driving it's fine, including very heavy throttle. At first I thought this was an ignition miss, but after checking all my ignition (and replacing a few parts), the problem still exsits. I believe that low fuel pressure can cause a symptom like this in these GM TBI engines. IFthe fuel pressure is low, does anyone know how to determine if it is a weak pump or a bad pressure regulator? Both are original in the truck, and I would prefer to replace only one at this time.

 

[kc8adu]

bad fpr causes it to lean out/bog at high load/rpm. gp sorenson makes the fpr kit INCLUDING the spring that is always broken.make sure you get the one with the spring as you WILL need it!its about $28. i had a similar problem that was a bad pickup coil in the distributer.had an intermittant cts plug cause intermittant dropout and backfiring through the tbi.would go open just long enough to make it spit but seldom long enough to set a code.would run fine for weeks and then spit anytime you made a sudden change like pulling out from a stop.

 

[Oldswagon]

The truck has a new AC-Delco pick-up coil and distributor shaft. I am thinking if this is an ignition problem, it might be a bad module, but I want to check the fuel pressure first to make sure that it's not the issue. That's why I want to know how to determine if the pump or the FPR is bad.

 

[vizvo]

If you are concerned with fuel pressure, you will need to buy a fuel pressure gauge. To test the regulator, with engine at idle, pull the vacuum hose off the regulator (cover the end of the vacuum hose with your thumb). The fuel pressure gauge should show several psi of increase in pressure. See your vehicle's shop manual for specs and details on using a fuel pressure gauge for testing fuel pressure. Don't overlook the TPS (throttle position sensor) they can go bad too, and develop "dead spots" due to wear.

 

[Oldswagon]

I am in the process of getting a fuel pressure gauge, but since the GM TBI systems need a special adaptor, I am likely going to have to order one. GM TBI systems have regulators that do not use engine vacuum. I know the fuel pressure is supposed to be 9-13 PSI on these systems. If the fuel pressure is below that spec, I just don't know how to determine what it causing the low pressure.

 

[kc8adu]

i doubt its a fuel pressure issue.i have never seen a gm tbi pump with low output.they just drop dead when they go.they warn you by screaming before they go. you will hear it unless you are deaf as it is a very irritating pitch.at your milage replace it and inspect the connectors on the sender/pump assy.see lots of them burned up. plugged filters are a common issue that can kill the pump too. if it were mine to fix i would take a ride with my 4 channel scope hooked up to pickup,coil primary,and a inductive pickup on coil secondary. let someone else drive.of course it will never act up again.