Bad Fuel Pump ???

[Gunny]

Quick disclaimer ... I've already searched our forum & have read as much as possible on fuel pump issues, replacement, etc.

My situation:
90 ZR-1 w/128,000 miles. I have all the service records since 70K miles and the fuel pumps have not been serviced/replaced during that time so I'm assuming that I have the original pumps.

Symptoms:
started about 2 weeks ago after not being driven for a couple of months. Engine started normally, no indication of problems, but the engine began "bucking" and cutting out/missing at 3000 rpm as if it had no fuel. It did not seem to be an ignition problem. Service engine light came on briefly but went out almost immediately. The engine missing occurs above 3000 rpm whether under load or not. After driving for 10 minutes or so, the missing stopped and everything seems normal ... full power, etc. A/C plugs & Accel injectors are all quite new, with only trips to BG & Carlisle ... fuel filter also fairly recent. Except for trips outside of my immediate area the Z always gets premium with NO ethanol (I have local access to non ethanol premium).

Analysis:
checked for loose vac hoses but no problem there. Put fuel pressure gauge on the rail and I'm reading 38lbs when key is first turned on. With engine on I have about 38-39 lbs at idle and with slightly higher RPM I get about 41-42 lbs. With engine not running and key on, the fuel pressure starts at 38 lbs but with each cycle of the pump turning on the pressure drops until it's down in the low 20's. If I charge the fuel rail up with key on and get the 38 lbs and then turn key off, the system holds the 38 lbs for quite a while (i.e. takes some time for the pressure to leak down). This is why I'm suspecting a fuel pump issue ... shouldn't I have 50+ lbs of fuel pressure?

In my mind it appears that I need to replace the fuel pumps but have I missed anything? Here's where I need the gurus to chime in ... Pete? others? any/all help & advice will be appreciated.

If I do need fuel pumps what's the best approach?
Rock Auto Part #P240KC. (Performance Electric) - less than $30 each
complete OEM kit - $345 from Jerry's Gaskets.
Obviously, a pair of pumps for $60 is more attractive than any more-expensive options but I don't want to make a bad decision on this issue.

I read the thread on the Bosch replacement requiring minor modifications (good writeup, btw) but I think I would prefer to replace without cutting, modifying, etc. I've never changed the fuel pumps on a Z (never have seen it done either) but it looks fairly straight forward. Any advice and/or tips would certainly be helpful.

Thanks in advance ... hope to see a bunch of good replies so I can get the Z back on the road. Any harm in driving it before I make repairs/replacements? ... or should I leave it parked? I just drove it again this morning hoping the problem had disappeared on its own, but alas, the first few times I hit 3K on the tach the engine began to cut out ... but after about 10 minutes all the symptoms were gone and everything seemed normal.

[zr1mom]

Hi George, my first thought might be the Fuel Pressure Regulator? Since the check engine light came on a code may have been set that might give you a hint as well.

[Gunny]

thanks ... hadn't thought about the FP regulator. Haven't pulled the codes yet but will do that also.

[ZZZZZR1]

George

Yun and I changed fuel pumps recently (for preventative maintenance) and I think we used suburban pumps @ $75 each. Check with Yun and see where he bought them.

Jim Voter might have the best way to test them

:cheers:

David

[Gunny]

Code 56 (assuming I pulled the code correctly) Any ideas?

[DaveK]

Code 56 - port throttle vacuum sensor?

[zr1mom]

Code 56 will be set when:
1. Vacuum sensor signal voltage is less than .46 volt at any time
2. Vacuum sensor signal voltage is greater than 5 volts at any time

This checks to see if there is a constant vacuum signal on the sensor at idle.
If the ECM recognizes the low vacuum signal, the ECM and wiring are OK.
If the ECM recognizes the high vacuum signal, the ECM and wiring are OK.

[zr1mom]

You might also check your secondary butterflies and make sure they are opening and not binding shut or sticking.

[Pete]

It sounds like secondaries if it's bucking/cutting out at 3k.

A quick simple test.

The MAP sensor under your ECM get a long piece of vecuum hose connect one end of the hose to the MAP sensor (under the ECM) connect the other end to your vacuum pump go for test drive.
If the bucking/cutting out goes away then look for vaccum leak or a bad electric secondary solonoid.

This is just a quick unorthodox diagnoses not a fix before you start throwing parts at her.

Pete

[Marc Haibeck]

Hi George,

Code 56 means that the secondary vacuum diagnostic sensor has an electrical fault. When code 56 sets a 3000 rpm rev limiter is imposed.

The sensor is located under the ECM mounting bracket. Maybe the electrical connector is loose. If there is a good electrical connection the sensor has probably failed. The sensor part is available because it is used by many other vehicles. GM PN 16231141.

[Hog]

16231141-Used in these vehicles
Make
Model
Engine
Year(s)
Buick
Century
2.8 L 173 CID V6
1986 - 1986
Buick
Electra
5.0 L 307 CID V8
1985 - 1987
Buick
Electra Estate Wagon
5.0 L 307 CID V8
1985 - 1987
Buick
Lesabre
5.0 L 307 CID V8
1985 - 1987
Buick
Regal
5.0 L 307 CID V8
1986 - 1987
Buick
Riviera
5.0 L 307 CID V8
1985 - 1985
Buick
Skylark
2.8 L 173 CID V6
1985 - 1985
Cadillac
Brougham
5.0 L 307 CID V8
1987 - 1987
Cadillac
Fleetwood
5.0 L 307 CID V8
1986 - 1986
Chevrolet
Camaro
2.8 L 173 CID V6
1985 - 1987
Chevrolet
Camaro
5.0 L 305 CID V8
1985 - 1987
Chevrolet
Camaro
5.7 L 350 CID V8
1987 - 1987
Chevrolet
Caprice
4.3 L 262 CID V6
1985 - 1985
Chevrolet
Caprice
5.0 L 305 CID V8
1985 - 1987
Chevrolet
Caprice
5.0 L 307 CID V8
1986 - 1988
Chevrolet
Caprice
5.7 L 350 CID V8
1988 - 1988
Chevrolet
Celebrity
2.8 L 173 CID V6
1985 - 1986
Chevrolet
Citation
2.8 L 173 CID V6
1985 - 1985
Chevrolet
Corvette
5.7 L 350 CID V8
1990 - 1991
Chevrolet
Corvette
5.7 L 350 CID V8 DOHC 32 Valve
1990 - 1995
Chevrolet
Impala
4.3 L 262 CID V6
1985 - 1985
Chevrolet
Impala
5.0 L 305 CID V8
1985 - 1985
Chevrolet
Impala
5.7 L 350 CID V8
1985 - 1985
Chevrolet
Monte Carlo
4.3 L 262 CID V6
1985 - 1985
Chevrolet
Monte Carlo
5.0 L 305 CID V8
1985 - 1988
Chevrolet Truck
Astro Van
4.3 L 262 CID V6
1985 - 1985
Chevrolet Truck
Blazer K5 1/2 Ton 4WD
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
Blazer S10 2WD
2.8 L 173 CID V6
1985 - 1985
Chevrolet Truck
Blazer T10 4WD
2.8 L 173 CID V6
1985 - 1985
Chevrolet Truck
Blazer V10 1/2 Ton 4WD
5.7 L 350 CID V8
1987 - 1987
Chevrolet Truck
C10 1/2 Ton - Pickup
4.3 L 262 CID V6
1985 - 1986
Chevrolet Truck
C10 1/2 Ton - Pickup
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
C10 1/2 Ton - Pickup
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
C20 3/4 Ton - Pickup
4.3 L 262 CID V6
1985 - 1986
Chevrolet Truck
C20 3/4 Ton - Pickup
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
C20 3/4 Ton - Pickup
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
C30 1 Ton - Pickup
5.0 L 305 CID V8
1986 - 1986
Chevrolet Truck
El Camino
4.3 L 262 CID V6
1985 - 1985
Chevrolet Truck
El Camino
5.0 L 305 CID V8
1985 - 1987
Chevrolet Truck
G10/1500 1/2 Ton - Van
4.3 L 262 CID V6
1985 - 1986
Chevrolet Truck
G10/1500 1/2 Ton - Van
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
G10/1500 1/2 Ton - Van
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
G20/2500 3/4 Ton - Van
4.3 L 262 CID V6
1985 - 1986
Chevrolet Truck
G20/2500 3/4 Ton - Van
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
G20/2500 3/4 Ton - Van
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
K10 1/2 Ton 4WD - Pickup
4.3 L 262 CID V6
1985 - 1986
Chevrolet Truck
K10 1/2 Ton 4WD - Pickup
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
K10 1/2 Ton 4WD - Pickup
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
K20 3/4 Ton 4WD - Pickup
4.3 L 262 CID V6
1985 - 1985
Chevrolet Truck
K20 3/4 Ton 4WD - Pickup
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
S10 - Pickup
2.8 L 173 CID V6
1985 - 1985
Chevrolet Truck
Suburban C10 1/2 Ton
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
Suburban C10 1/2 Ton
5.7 L 350 CID V8
1985 - 1986
Chevrolet Truck
Suburban C20 3/4 Ton
5.0 L 305 CID V8
1985 - 1986
Chevrolet Truck
Suburban K10 1/2 Ton 4WD
5.7 L 350 CID V8
1985 - 1986
GMC Truck
C1500 1/2 Ton - Pickup
4.3 L 262 CID V6
1985 - 1986
GMC Truck
C1500 1/2 Ton - Pickup
5.0 L 305 CID V8
1985 - 1986
GMC Truck
C1500 1/2 Ton - Pickup
5.7 L 350 CID V8
1985 - 1986
GMC Truck
C2500 3/4 Ton - Pickup
4.3 L 262 CID V6
1985 - 1986
GMC Truck
C2500 3/4 Ton - Pickup
5.0 L 305 CID V8
1985 - 1986
GMC Truck
C2500 3/4 Ton - Pickup
5.7 L 350 CID V8
1985 - 1986
GMC Truck
Caballero
4.3 L 262 CID V6
1985 - 1985
GMC Truck
Caballero
5.0 L 305 CID V8
1985 - 1987
GMC Truck
G1500 1/2 Ton - Van
4.3 L 262 CID V6
1985 - 1985
GMC Truck
G1500 1/2 Ton - Van
5.0 L 305 CID V8
1985 - 1985
GMC Truck
G1500 1/2 Ton - Van
5.7 L 350 CID V8
1985 - 1985
GMC Truck
G1500 Rally Wagon - Van
5.7 L 350 CID V8
1986 - 1986
GMC Truck
G2500 3/4 Ton - Van
4.3 L 262 CID V6
1985 - 1985
GMC Truck
G2500 3/4 Ton - Van
5.0 L 305 CID V8
1985 - 1985
GMC Truck
G2500 3/4 Ton - Van
5.7 L 350 CID V8
1985 - 1985
GMC Truck
G2500 Rally Wagon - Van
5.7 L 350 CID V8
1986 - 1986
GMC Truck
G3500 1 Ton Rally Wagon - Van
5.7 L 350 CID V8
1986 - 1986
GMC Truck
G3500 1 Ton - Van
4.3 L 262 CID V6
1985 - 1986
GMC Truck
G3500 1 Ton - Van
5.7 L 350 CID V8
1985 - 1986
GMC Truck
G3500 1 Ton Vandura Cargo - Van
5.7 L 350 CID V8
1986 - 1986
GMC Truck
Jimmy K1500 1/2 Ton 4WD
5.0 L 305 CID V8
1985 - 1986
GMC Truck
Jimmy K1500 1/2 Ton 4WD
5.7 L 350 CID V8
1985 - 1986
GMC Truck
Jimmy S15 2WD
2.8 L 173 CID V6
1985 - 1985
GMC Truck
Jimmy T15 4WD
2.8 L 173 CID V6
1985 - 1985
GMC Truck
Jimmy V1500 1/2 Ton 4WD
5.0 L 305 CID V8
1987 - 1987
GMC Truck
Jimmy V1500 1/2 Ton 4WD
5.7 L 350 CID V8
1987 - 1987
GMC Truck
K1500 1/2 Ton 4WD - Pickup
4.3 L 262 CID V6
1985 - 1986
GMC Truck
K1500 1/2 Ton 4WD - Pickup
5.0 L 305 CID V8
1985 - 1986
GMC Truck
K1500 1/2 Ton 4WD - Pickup
5.7 L 350 CID V8
1985 - 1986
GMC Truck
K2500 3/4 Ton 4WD - Pickup
4.3 L 262 CID V6
1985 - 1985
GMC Truck
K2500 3/4 Ton 4WD - Pickup
5.7 L 350 CID V8
1985 - 1986
GMC Truck
S15 - Pickup
2.8 L 173 CID V6
1985 - 1985
GMC Truck
Safari Van
4.3 L 262 CID V6
1985 - 1985
GMC Truck
Suburban C1500 1/2 Ton
5.0 L 305 CID V8
1985 - 1986
GMC Truck
Suburban C1500 1/2 Ton
5.7 L 350 CID V8
1985 - 1986
GMC Truck
Suburban C2500 3/4 Ton
5.0 L 305 CID V8
1985 - 1986
GMC Truck
Suburban C2500 3/4 Ton
5.7 L 350 CID V8
1985 - 1986
GMC Truck
Suburban K1500 1/2 Ton 4WD
5.7 L 350 CID V8
1985 - 1986
Oldsmobile
Cutlass
3.8 L 231 CID V6
1985 - 1985
Oldsmobile
Cutlass
5.0 L 307 CID V8
1985 - 1987
Oldsmobile
Cutlass Ciera
2.8 L 173 CID V6
1986 - 1986
Oldsmobile
Delta 88
3.8 L 231 CID V6
1985 - 1985
Oldsmobile
Delta 88
5.0 L 307 CID V8
1985 - 1985
Oldsmobile
Toronado
5.0 L 307 CID V8
1985 - 1985
Pontiac
6000
2.8 L 173 CID V6
1985 - 1986
Pontiac
Bonneville
5.0 L 305 CID V8
1985 - 1986
Pontiac
Firebird
2.8 L 173 CID V6
1985 - 1987
Pontiac
Firebird
5.0 L 305 CID V8
1985 - 1987
Pontiac
Firebird
5.7 L 350 CID V8
1987 - 1987
Pontiac
Grand Prix
5.0 L 305 CID V8
1985 - 1987
Pontiac
Parisienne
5.0 L 305 CID V8
1985 - 1986
Pontiac
Parisienne
5.0 L 307 CID V8
1986 - 1986
Pontiac
Safari
5.0 L 307 CID V8
1987 - 1987



peace
Hog

[A26B]

started about 2 weeks ago after not being driven for a couple of months


Given your humid environment George, you should make an effort to keep your gas tank full at all times. otherwise the fuel sender assy will rust....badly and wreak havoc with pumps & filters, resulting in low fuel pressure among other symptoms.
http://i190.photobucket.com/albums/z224/A26B/FuelPumpAssy.jpg
I had to siphon LOTS of rust from the bottom of the fuel tank after this one was pulled.

If the recommended correction for DSC 56 doesn't cure what ails, I would suggest you pull the fuel pump sender assy to look at it before you order any parts & do filters at the same time.

The rough running for 10+ minutes is also a symptom of bad fuel in the injectors from sitting too long without Sta-bil fuel stabilizer in the fuel.

A full tank with fuel stabilizer during inactive periods will prevent problems.

[Gunny]

Hi George,

Code 56 means that the secondary vacuum diagnostic sensor has an electrical fault. When code 56 sets a 3000 rpm rev limiter is imposed.

The sensor is located under the ECM mounting bracket. Maybe the electrical connector is loose. If there is a good electrical connection the sensor has probably failed. The sensor part is available because it is used by many other vehicles. GM PN 16231141.

The electrical connection was not loose but I did clean the contacts and plugged it back in. The problem appears to be solved and the only way that I can duplicate the symptom is to disconnect the electrical connector ... so I think (hope) everything is OK.

I have not re-checked the fuel pressure but if it is still below 40 lbs I'm wondering if I will need to address a fuel pump issue in the future. At the moment everything seems to be OK.

Thanks to all who responded and a special thanks, as always, to Marc for his insight & advice.

George

[scottfab]

...snip...

I have not re-checked the fuel pressure but if it is still below 40 lbs I'm wondering if I will need to address a fuel pump issue in the future. At the moment everything seems to be OK.

...snip....

yes at least one pump is bad. Below 40 is too low.

[Gunny]

Given your humid environment George, you should make an effort to keep your gas tank full at all times .... A full tank with fuel stabilizer during inactive periods will prevent problems.

Thanks for the reminder, Jerry. SOP for me is to always fill the tank before parking in the garage unless I know that I will have 3-4 short trips within a week. I've never used fuel stabilizer since I normally drive the Z at least once a week. Mid-October until late December ended up being especially bad for driving the Z since I was out of town (mostly in TX) during this time period.