Schurkey

This seems to be the finest web site in existence for TBI information. While I recognize that this is primarily a Camaro/Firebird site, much of the information applies to GM TBI vehicles in general.

In my case, I have an '88 Chevy K1500 work truck with the VIN K 5.7L engine.

The truck has about 300,000 miles; and in the hundred and thirty thousand miles that I've had it, it's never had the fuel pump replaced. God only knows how old it is. I did some research on this site; the Airtex E3210 and Delco EP241 fuel pumps for TPI vehicles have been recommended as a common upgrade.

I accessed the fuel tank by removing the truck bed. Luckily, it's now a "Fuel saving light weight" bed. Notice the extra ventilation holes provided by Wisconsin and Minnesota salted roads.



Fuel pump hanger and sending unit is now easily accessed.



I ordered the Airtex E3210 pump.


The damned thing is a Communist import. These pumps are hard enough to deal with, I WILL NOT trust Communist child-labor for something this critical. I sent it back and ordered a Delco EP241 instead.



This Delco pump is made in USA, although they aren't saying where the accessories packaged with the pump come from. About ten bucks more than the Airtex; and well worth it. You may want to verify that they're STILL made in the USA.

I compared the original TBI pump that was in my truck to the new EP241 pump:






Although the molding around the electrical connector seems different, the wire harness plugs into either pump just fine.




The pumps clearly are not identical; but the new one fits nicely in place except for the fuel discharge port. The old pump discharge--and the metal tubing of the hanger assembly--is 3/8 inch; while the new pump has a smaller, 5/16 discharge port. I thought of a few clever and time-consuming ways to deal with the size difference, and then decided to just cram the 5/16 hose over the 3/8 tubing of the hanger assembly. Seemed to work OK once I lubed the metal tubing so it would slide inside the hose easier. I installed two genuine "fuel injection" hose clamps on the tubing instead of the cheap worm-gear clamps supplied with the pump.

The tank should be cleaned out so there is no dirt or rust particles inside. Contamination of the fuel is a leading cause of fuel pump failure. My tank looked pretty good inside. I had some fun trying to get the new fuel strainer installed on the bottom of the pump. Man, that's tight! Took awhile, but I did get it shoved into place.

With the new pump installed in the hanger, and the hanger installed in the tank, I decided to do some electrical analysis before re-installing the truck box.

Schurkey

I have an ancient Snap-On Counselor II oscilloscope and the low-amps current probe to measure current flow. (Not shown: I used a plain ol' multimeter to determine the voltage driving the fuel pump--13.2 volts at the input to the sending unit.) Measure the voltage as closely to the sending unit as possible. Amperage can be measured anywhere in the circuit, but voltage must be measured close to the actual load.

The fuel pump amperage draw with the engine idling looked like this:



There is a gridwork on the screen. The dotted line at bottom of the photo represents "0" volts. The horizontal line above it is 2 volts, the one above that is 4 volts, and the one above that--where the squiggly line is--would be 6 volts. An oscilloscope shows a graph of time (horizontal axis) versus volts (vertical axis) The Snap-On current probe represents one amp of current as one volt. Six amps measured by the current probe = six volts shown on the 'scope. The new fuel pump is therefore drawing a bit less than six amps of current on average, although the peaks are a bit more than six amps.

If you look REALLY CLOSELY, you'll see that the pattern of squiggles (humps) repeats. There are eight distinctive shapes to the humps, the ninth hump is the same as the first, the tenth is the same as the second, etc. This is because Delco fuel pumps have eight bars on the armature commutator. Other fuel pumps may have a different number of commutator bars. One turn of the armature allows all eight bars of the commutator to align with the brushes, when each bar is perfectly aligned with the brush, maximum current flows. In a perfect world, each hump would be a perfect match to every other hump. This is not a perfect world, and each hump has it's own "fingerprint" if you look closely enough.

Why is this important? If you can determine visually where the pattern repeats, the oscilloscope can show you how long in milleseconds that it takes for the pattern to repeat. The photo below is the same pattern, but with cursor lines (vertical solid and vertical dashed; horizontal solid and horizontal dashed) that give us a time and voltage (and remember, one ampere of current is represented as one volt.)



(In this case, I'm concentrating on the two tallest humps.)

I put a vertical (dashed) cursor through the peak of a hump, and then the other vertical cursor (solid) through the peak of the ninth hump to the right--exactly where the pattern repeats. This represents the time it takes for the pattern to repeat, (which would be one revolution of the electric motor.) The time measurement for ONE revolution is 10.16 milleseconds.

Why is that important? There are 60,000 milliseconds in one minute. Divide 60,000 by 10.16, and we determine that the electric motor driving the fuel pump is turning 5905 rpm. This is in line with what would be expected--but don't think the fuel pump manufacturer is going to provide specification that we can use to determine if the pump is running too fast or too slowly.

The horizontal cursors--solid at the bottom and dashed at the top--are showing the peak current draw of the motor--6.444 volts on the 'scope is the equivalent of 6.444 amps. Again, right in line with what I'd expect, MAYBE a little higher than I'd expect considering the typically low TBI fuel pressure, and again, don't think you're going to find "official" specs.

What's missing? Good question. While doing this work, I do not have access to a fuel pressure tester. The adapter I ordered fits the vehicle, but does not thread into my pressure gauge. In this case, I SUSPECT that the fuel pressure is in the typical TBI range of 10--11 psi. [Later edit: Fuel pressure is 11.5 psi]

Amperage, RPM, Voltage at the pump, and fuel pressure are all interrelated. High fuel pressure at the pump due to a plugged fuel filter may cause high amperage draw, and lower RPM. Low voltage because of corroded connections can cause low rpm, and low pressure. If one or more "humps" is WAY different looking from the others, the pump motor is dying. Oscilloscope pattern testing of fuel pumps is a wonderful way to verify pump condition.

Hand-held 'scopes are becoming more common and less expensive. I'll make do with the Counselor II for awhile yet, though.

UnderCover89TBI

iTrader: (25)

so the purpose of the thread is to show people how to change the fuel pump I am assuming?

Schurkey

Several purposes:
1. I had a hellish time getting information on the various fuel pumps. Manufacturer web sites don't show much information; and so--in frustration--I wound up with two "recommended" pumps. I wanted to show what to expect with the two units. In particular, the Delco EP241, since the Airtex was never taken out of the bag it came in.

2. Oscilloscope testing of fuel pumps--measuring pump RPM and current draw of a new (and supposedly not defective or damaged) pump so that others with similar pumps could have a baseline measurement for diagnostic purposes. Even if you do amperage testing with a multimeter, you might not know how many amps a pump like this typically draws. (Side benefit--oscilloscope testing of other electric motors is done with a similar process. You could test electric cooling fans, the heater/air conditioning blower motor, etc.)

wahoo

The french sentence "Pompe à carburant" written on the box of the part made in USA is correct.
But, on the box of the part made in China, I don't know, even if i can imagine, what does the sentence written in "french" mean...
For my american car, I prefer buying a part made in USA instead of buying a part made in an exotic foreign country. And you can believe a french camaro owner living in France. It costs me more to buy a part in USA, but I know the parts live longer and there are less problems to mount them on the car.

Very interesteting and informative topic. Thanks.

82CrossFire Z28

iTrader: (1)

A loose translation is "fuel pump" for "Pompe à carburant". I think a more literal translation would be "pump of (the) carburetor".

Just do a Goggle search on the phrase and the select the "translate this page" link on the may French pages the search engine returns.

wahoo

No "Fuel pump" means "Pompe à essence" or "Pompe à carburant", carburant means all types of fuel....
But on the box of the part made in China, it's written "Fabriqué aux China" instead of "Fabriqué en Chine"... The false sentence means the part is made in several countries named China.

Schurkey

First Guess: Something else the Chinese have screwed up.