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Fuel pressure failure

R

roadster

Guest
Hi there vette lovers..I´m having some trouble with my 90 Zr1. My fuel pressure drops just after my engine fires up, and the engine stalls. Seems maybe like a fuel pump problem, but this symptom only occurs after engine is hot. Both pumps have a staddy pressure of 50-55 psi first 10 to 20 miles, but then if I turn the engine off and restart the engine stalls after a few seconds with pressure dropping.
Would really appreciate some help, ain´t that many zr1 mechanics around here in Sweden..Is the car suppose to run on primary pump? Where is the pump relay located? Read here in the 84-96 forum that the oil pressure sensor could make the pump relay open circuit, does that apply to the zr1. Guess I´m in to some troubleshooting...

Thanks PA..
 

Rodder

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Joined
Jun 10, 2002
Messages
3
Location
Sweden
Corvette
-90 ZR-1
Hey.
Im not an expert but it sounds like your car could only be running on the secondary pump. To my knowledge the car when cold use both pumps and then the secondary shuts off.
You have the fuse for primary pump in the fuse box named FP1. Fuse for the secondery is under the instruent panel on passenger side in the axuiliary fuse block, FP2. Pull FP2 fuse and check the pressure. Should read 48-55psi.
The relays are under the instument panel aswell. Hard to explain which ones they are but i give it a try.
On drivers side you have the secondary relay. Turn on your turning flasher and find that relay by sound. To the right of that relay you have two relays more. The one to the right of those(cars right side) is the FP 2 relay.
The primary relay is on the passenger side. If you search under there you see 5 relays mounted like, 2 and then 3 beside one another. The right one of the "3 together". Or maybe i should say the middle one of all five relays is the FP1 relay.

Not sure about the oilpressure sender. Believe i read ppl having running cars but no oilpressure when the sensor gone bad so im not sure about it shuting down FP´s. When you see oil in the sender, like around the cable connection, then its broke. I orderd me a new one this morning, my gauge went nuts. So today im gonna say a pray, change oil and cut the oilfilter open looking for bearing parts. Man, i so hope i dont find any !!! Engine made no sounds or nothing was just the gague went too low. So there is hope.

Hope you are got some help from this. And it sure aint easy finding help here. Yep im live in Sweden aswell. Got me a 90 ZR too.

And hey, if someone see anything wrong here, feel free to correct me.

/Rodder
 

Rob

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1990 Corvette ZR-1
Unfortunately, the only thing I can say is that the engine runs off the primary pump at all times. The secondary pump only comes online when the secondaries open in order to meet the demand for increased fuel consumption.
 

Rodder

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Jun 10, 2002
Messages
3
Location
Sweden
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-90 ZR-1
Hi Rob.
Why should you, according to service man, then pull the fuse for FP2 to check the primary fuel pump pressure if the 2nd pump dont run below 3500rpm?

/Rodder
 

FrankUrbinati

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Sep 7, 2001
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113
Location
Babylon NY
Corvette
1991 White ZR1-93 Green ZR1/LSV 385 98 Convert.
The service manual for the LT5 has a section on how to diagnose fuel related problem's. You can start with using a fuel pressure guage. The fuel pressure should be 43lb's at idle. And 50lb's at WOT.
 

WhalePirot

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Messages
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SoCA
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1984 White Z-51/ZF6-40/Shinoda body
I suspect the primary fuel pump.

Both fuses are an easy check.

You may tape a fuel pressure gauge to the windshield, to observe the fuel pressure while cranking. Normal fuel pressure with ignition on but not running, is listed below. At idle or with 10 inches of vacuum, the pressure should drop by 3-10psi (21-69kPa).

You should have a check engine light when turning the key ON, before starting. Grounding the test terminal should give a '12' (indicating a 12v test signal, BTW) then, any trouble codes.

Test A-3 is for: "the engine runs fine until hot, then stalls. I can crank but it will not stay running. After it cools, it starts and runs fine." Sound familiar?

At a coolant temperature above 80C, the secondary fuel pump is deenergized by the ECM. The engine will stall if the CKT 120 or the primary fuel pump are faulty. Below 80C, both fuel pumps are energized. (This is probably like the cold start injector on early port injected cars, later replaced by ECM control.)

Chart A-3: With good spark (a lengthy
process seemingly not applicable), disconnect #2 primary injector (gray) and connect injector test light to the harness. Crank and look for blinking light. No flash means a faulty ECM; Yes> check pre-cranking fuel pressure (48-55 psi, or 333-376kPa).

If good pressure, pull FP2 and check fuel pressure (same). If okay, the fuel injector system is okay. If not, Chart A-7 applies.

If low pressure with FP2 pulled, there is a faulty connection or open CKT 120 (feed from FP1 to pump 1)

The service manual shows: a fuel pump test connector (near the the battery) as a red (#490) wire, feeding the primary fuel pump relay, at terminal 3. #2 is ground. #5 comes from the ECM to trigger the relay, while #4 is power to operate the relay, fed from the fusible link; also feeding the ignition switch and fuse block.

#1 terminal on the Primary fuel pump relay connects (red wire) to FP1, a 10 amp fuse, which feeds two gray wires to the primary pump and the ECM (voltage monitor). That red wire also feeds terminal #1 on the 2ndary fuel pump relay, whci is switched in the relay to feed an orange wire on terminal 3, to FP2 (10amp) fuse (aux fuse box), then on to that pump.

Too much detail, above?

Sounds like the primary pump or power to it has failed. I think ECM failure is a much lower probability. I surmise that pulling fuse FP2 and trying a cold start will show the #1 pump to be out, as indicated by a no start.

Ain't this fun?

Buy a Service manual, and study it. The manuals refer to a lot of fancy gear, but understanding that these are still engines, requiring fuel and spark, with easy, and basic checks like we've done for years still enable 'us' to find the problem. The ECMs merely do a more precise job of controlling the engine than the old jets, vacuum advance and such simple devices. They are not magic; just use electric sensors and controls to increase precision. They are quite reliable, with mechanical failures and/or sensor failures causing the 'brain' problems.
 

Rob

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Rodder said:
Hi Rob.
Why should you, according to service man, then pull the fuse for FP2 to check the primary fuel pump pressure if the 2nd pump dont run below 3500rpm?

/Rodder

I'm not qualified enough to give you an answer to this question. All I can say is, as stated on page 2-2 of the LT5 Fuel and Emissions Manual is:

....the secondary fuel pump is energized only during secondary throttle system operation through one of the two fuel pump relays....

From 2-3:
The fuel pump relays are used by the ECM for control over the primary and secondary fuel pumps. There are two relays, one for control over each pump. The ECM energizes these relays by providing source voltage (B+). When the relays are energized, the fuel pumps are running.

The fuel pump relays are located at the rear of the left hand front wheel well inside the engine compartment.
 

WhalePirot

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1984 White Z-51/ZF6-40/Shinoda body
I paraphrased and quoted the 1990 service manual from the fuel delivery section, troubleshooting; specifically the hard start when hot page.

I think Rob is saying the same thing, but during the cold start, the ECM seems to use the secondary system to enrich the mixture. Of course, this is not needed when the engine is started hot. As a hot starting problem, methinks the fix lies therein, not under RPM requirement for secondary injectors.

How do you do all those cool graphics? HE waves!
 

Rodder

New member
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Jun 10, 2002
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Corvette
-90 ZR-1
Rob.
WhalePirot already answerd about the pump(s). Fact is that 2nd pump actually runs more than just when secondaries are in action. I never meant that it runs at all times, sorry if i expressed myself that way before. And i didnt mean to question you or anybody here. Im just trying to learn, understand, help and trying to keep things straight, as im sure everybody here is aswell. You need to know how,what and why if you gonna try troubleshoot or do just whatever work on you car.

Well, i use factory SM and i cant find your qoute. But then again, me and books... Found this though.

Quote SM Engine Fuel 6C-3
Fuel pumps.
"The secondary pump is used only during cold engine cranking and operation, during periods of secondary injector operation, and during periods of engine operation when code #14 or #15 has been stored by the ECM."

And the relays are located as shown in 8A-201-9 / 201-13 under the intsrument panel.

But hey, this was about roadster having problems. Hows it going, you got that car running yet ? Give us a update.

:w

/Rodder

*edit.. i cant spell..*
 
R

roadster

Guest
primary pump

Must thank everybody for there great info, it helped a lot...

It took three days until I got fuel pressure failure again, and this time I was prepared! Checked power to relay ok, relay to pump ok, and grd ok. The engine starts but, stalls after a couple of seconds, and it turns out that fp2 build up pressure with key on, but fp1 is dead..so the car fires up but wont idle without fuel from primary pump.I then pulled fuse to fp2 and the engine wouldn´t even start. My conclusion is that fp1 fails to operate when hot and needs replacement!

Time to buy a primary pump, so I called the dealer only to find out that I had to buy the hole fuelassembly with both pumps and connections 2400$ I thought no way! It should be possible to find a single pump that fits, maybe from a L98 or Lt1. If anyone knows where to find a primary pump that fits my 90 zr1 I´ll be grateful.....

Ps lucky me that world cup is on now when my vette is parked in the garage!!!
 

Demps

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Apr 26, 2002
Messages
54
Location
niceville, fl USA
Corvette
95 ZR-1
As I thought, primary dead. Master makes a direct replacement pump. Be sure to buy a new screen (filter) as well. You need to get on the zr1 net. There is a lot of expertise there. Search their archives at WWW.corvettemuseum.com and look at the how to pages. It's all explained. I did this on my 95 for a weak pump and it was simple to do. $70 for pump.

cheers
ted
 
S

secondchance

Guest
Talking w/ vette mechanic, I was told that the pump is welded to the assembly and re-attaching a new pump to the assembly is impossible. And yet, based on an how to article in ZR1 net, there is np mention as to how the pumps are attached to the fuel pump assembly. Has anyone actually replced a pump? And if so, please clarify this issue.

Thanks.
 

Demps

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Apr 26, 2002
Messages
54
Location
niceville, fl USA
Corvette
95 ZR-1
the filter and the wiring harness hold it in a bracket on the fuel sender assembly. easy fix to do it yourself. took me a half hour.
 

Rob

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Vettaholic,

In the latest issue (Sept. 2002) of Corvette Fever Magazine is a how-to article on replacing the primary pump on the ZR-1 without replacing the entire assembly. It can be done. Look for it at your local newstand in the center of McLean. If it's not there and you need a copy of the article, let me know and I'll photocopy it and meet you in McLean sometime this weekend.
 
S

secondchance

Guest
Thanks Rob. I'll look for the mag. If I can't find it, I'll let you know.
 
S

secondchance

Guest
Rob,
Thanks, I did pick up a copy of the Corvette Fever. However, I am begining to suspect partially collapsed cat on the driverside.

Yun
 
S

secondchance

Guest
Well, with short connection for the fuel gauge, I could'nt get the reading while I am driving around but at idle and while reving I was getting 42 psi . Release the throttle, around 36 probably due to engine vacuum. I was going to replace the primary pump just in case. Then in the same magazine tech Q & A section, this guy was talking about simmilar pinging and hesitation for LT-1 and reading the article, I figured I better check the cat first. Now these cats are $900 each! Also, 2 months ago, when I had a mechanic hook up tech 1 or tech 2 scanner, he told me that the right bank O2 sensor values were ok. But the left bank value was fluctuating wildly. It may be that the clogged cat may result in O2 sensor thinking its lean, richening the fuel which does'nt solve the problem making ECM go back and forth. What do you think?
 

FrankUrbinati

Well-known member
Joined
Sep 7, 2001
Messages
113
Location
Babylon NY
Corvette
1991 White ZR1-93 Green ZR1/LSV 385 98 Convert.
Check out your fuel pressure. 42lbs at idle and 50ibs at WOT. Fuel filter ok ? A bad cat will usually will make a rattle that can be easily heard from the outside of the car. Also check the ohm's on all the injector's. Do you have a shop manual ? Those manual's help out alot.
:w
 

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