Update on hesitation up to 3,000 RPM,then,clears itself..

[Vette73]

Car is fine upon start up and for the first ten mins or so......After that, hesitation bogging until 3,000 rpm....

So, I'm guessing primary fuel pump..50,000 miles I have and I'm guessing original pumps....

Bought my car around to my mechanic and make a long story short I have the fuel pumps out of the car.....Weird thing is today I'm driving back from there ( short distance)
,service engine light comes on but now car is running fine.....Get home and I parked it....Ten mins later I get into car and I figured I would just bring it back and get it scanned

Got a few blocks ( no service engine on light) and car started to do the original symptoms-- bogging until 3,000 rpm...

Just took it home parked it and removed the fuel pumps.....

Wonder why light came on but ran fine with the service engine light on....

Will keep everyone posted after I put the new fuel pumps in...

Peace...

[RussMcB]

When I had problems with my car not running well I attached a fuel pressure gauge to the fuel rail so I could see if the pressure was dropping at the same time the engine started running bad. That at least tells you if the problem is with fuel pressure.

Later I decided to install a permanent FP gauge in the car (but I never look at it now).

Good luck.

[tomcat]

Hello,

Have you swap out the fuel filter? Maybe an o2 sensor or EGR component maybe bad.
Manfred E....
91 ZR1 #906

[Vette73]

Hello,

Have you swap out the fuel filter? Maybe an o2 sensor or EGR component maybe bad.
Manfred E....
91 ZR1 #906
Swapped out fuel filter about 6,000 miles ago....Will see when I change pumps..

[G8nightman]

You should get the codes first it will tell you what it is and there’s a few ways to test the pumps


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[Paul Workman]

I agree w/ others - TEST FIRST, replace after first determining (whatever) is actually bad. Never throw parts at a problem in hopes it goes away (which seems to be SOP for many (so-called) "mechanics".:mad:)

And, BTW, one of the best tools I ever bought for my first C4 was a scanner which could pull codes as well as give real time readings of 41(!) different parameters, AND featured the ability to record the dynamic sensor values when a problem was happening by pushing an "event" button. Saved me untold amounts of frustration - BELIEVE ME!

(NOTE: I've found that fuel related issues (for one) don't always throw a code right away, especially errant O2 readings don't immediately result in a code. (Marc Haibeck could tell ya for sure, but it seems the programming gives whatever is resulting in bad readings from the O2s a little time for the situation to truly establish itself as "real", before tossing a code: something to keep in mind.))

Getting ahead of the game, I attached pix of how to monitor fuel pressure under actual driving conditions, AND showing how and where to diagnose fuel pump current draw (and what the readings indicate).

[Vette73]

I guess I should have listened...I swapped out the fuel pumps and its still doing it...

I did the repair myself so I only paid for parts.....Funny thing is,the service engine soon light comes on and the car runs fine with the light on.....

I don't have any gauges so I will get it scanned at my mechanic this week..

[Demps]

http://www.zr1specialist.com/HAT%20Web/Tech%20Info/aldl.htm

I would use the link above with a paperclip & see if the code is residual.

Ted

[Pete]

Hi John

If i had to guess, you have FIC injectors?

Pete

[Vette73]

Hi John

If i had to guess, you have FIC injectors?

Pete
Hi Pete...
I believe accel..

[Pete]

I seen your symptoms on 2 cars and both had FIC's.
Usually its something silly.

Have you change anything recently?
Coils?
Wires?
MAP?
What spark plugs are in it?
What gap?

Pete


Hi Pete...
I believe accel..

[Vette73]

I seen your symptoms on 2 cars and both had FIC's.
Usually its something silly.

Have you change anything recently?
Coils?
Wires?
MAP?
What spark plugs are in it?
What gap?

Pete

Have not changed anything personally myself lately.....Put about 2,000 miles on it since I got it back last Dec from Dempsey..

Have to bring it around to my mechanic to have it scanned .....

[Hib Halverson]

I feel that this thread offers a great lesson on why any DIY working on engine controls of C4 ZR-1s or any other GM car for that matter, needs to own a scan tester capable of connecting to pre-96 ECMs. It's also a good lesson on why any DIY working on engine controls ought to have a Factory Service Manual.

The scan tester would tell you what fault code has set or is setting. It will also tell you if the fault code is a history code, ie: the fault is not present right now, but was present sometime in the last 50 ignition cycles. I suggest that when the engine light is on, check codes first then buy parts.

The FSM would tell you not only how to properly test fuel pressure, but, in the case of a C4 ZR-1, it also will tell you how to test each of the two pumps separately. It also tells you where the fuel pump test connection is located.

So, the car has a recent fuel filter change and two new fuel pumps...is the engine light still coming on? If so, the first thing I'd do is use flash code diagnostics (you can do it with the paper clip discussed in an earlier post) to get current fault codes out of the ECM then post them here.

Finally, I did not see the model year of the car in the OP, but there are some model years of C4 ZR-1s which will display ECM fault codes in the IP display. If your model year is one of those which can do that, using the IP display to show ECM faults is another good way to go if you don't have a scanner.

[Vette73]

I feel that this thread offers a great lesson on why any DIY working on engine controls of C4 ZR-1s or any other GM car for that matter, needs to own a scan tester capable of connecting to pre-96 ECMs. It's also a good lesson on why any DIY working on engine controls ought to have a Factory Service Manual.

The scan tester would tell you what fault code has set or is setting. It will also tell you if the fault code is a history code, ie: the fault is not present right now, but was present sometime in the last 50 ignition cycles. I suggest that when the engine light is on, check codes first then buy parts.

The FSM would tell you not only how to properly test fuel pressure, but, in the case of a C4 ZR-1, it also will tell you how to test each of the two pumps separately. It also tells you where the fuel pump test connection is located.

So, the car has a recent fuel filter change and two new fuel pumps...is the engine light still coming on? If so, the first thing I'd do is use flash code diagnostics (you can do it with the paper clip discussed in an earlier post) to get current fault codes out of the ECM then post them here.

Finally, I did not see the model year of the car in the OP, but there are some model years of C4 ZR-1s which will display ECM fault codes in the IP display. If your model year is one of those which can do that, using the IP display to show ECM faults is another good way to go if you don't have a scanner.

Ok car is a 91 modified not stock...Dragon heart package by evolution.....After about ten mins of driving idle starts to drop and runs rough until 3,000 RPM than clears itself....

Hey, I thought it was the primary pump...Figured I would take a shot....

Engine light comes on after about a minute of it running rough.....Funny thing is, when engine light is on the car runs fine....Now, I'm not cruising around like this.....When it started to run rough,I was about ten minutes from my house and returned car to my garage the few times I checked it out...

I will have it scanned by my mechanic this week since I know nothing about codes and such....

Will show him this post and update the findings on the forum....

👍👍👍

[G8nightman]

I would guess it’s a bad O2 sensor.


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[WARP TEN]

I would guess it’s a bad O2 sensor.


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My thought too.--Bob

[XfireZ51]

Ok car is a 91 modified not stock...Dragon heart package by evolution.....After about ten mins of driving idle starts to drop and runs rough until 3,000 RPM than clears itself....

Hey, I thought it was the primary pump...Figured I would take a shot....

Engine light comes on after about a minute of it running rough.....Funny thing is, when engine light is on the car runs fine....Now, I'm not cruising around like this.....When it started to run rough,I was about ten minutes from my house and returned car to my garage the few times I checked it out...

I will have it scanned by my mechanic this week since I know nothing about codes and such....

Will show him this post and update the findings on the forum....

👍👍👍

All u need to do is go to AZ or Advance and buy one of these

https://shop.advanceautoparts.com/p/actron-obd-i-code-scanner-for-1982-1993-gm-vehicles-cp9001/9090223-p?c3ch=PLA&c3nid=9090223-P&adtype=pla_with_promotion&gclid=Cj0KCQjwguDeBRDCARIsAGxuU8b1Fi5MQo-HuFfGvbEDV-K_LTL68MTRrCz6f7vry8VddTGZXEKN60IaAtkhEALw_wcB&gclsrc=aw.ds

Then watch the SES light flash. Count the number of flashes. It will flash the first digit of the code then the second, and it will do that three times before moving on to any other codes. when u first start it will flash SES ONCE followed by TWO flashes for a CODE 12 which says the ECM is ok. It will then follow with any other code in the same manner.

[Vette73]

All u need to do is go to AZ or Advance and buy one of these

https://shop.advanceautoparts.com/p/actron-obd-i-code-scanner-for-1982-1993-gm-vehicles-cp9001/9090223-p?c3ch=PLA&c3nid=9090223-P&adtype=pla_with_promotion&gclid=Cj0KCQjwguDeBRDCARIsAGxuU8b1Fi5MQo-HuFfGvbEDV-K_LTL68MTRrCz6f7vry8VddTGZXEKN60IaAtkhEALw_wcB&gclsrc=aw.ds

Then watch the SES light flash. Count the number of flashes. It will flash the first digit of the code then the second, and it will do that three times before moving on to any other codes. when u first start it will flash SES ONCE followed by TWO flashes for a CODE 12 which says the ECM is ok. It will then follow with any other code in the same manner.

Ok great ...Will look into this...Thnx

[Vette73]

Update...Shout out to all those on the registry in helping me solve this issue..

From learning to decipher codes with a paperclip to fuel pump replacement..

End result,it was an 02 sensor..6 flashes followed by 5 flashes running rich, than tanking...Thank you George Maz and G8nightman..

[XfireZ51]

Did u resolve the issue or just determine the MALF code?

[Vette73]

I changed the 02 sensor on the passenger side..Problem solved...However, the one I got from jerrys gaskets denso was too small....Wound up getting one from Amazon the same day because I needed the car today...

If your making extensions for the 02 sensor I will take one.....Would like to run the same brand 02 sensors,just need an extension for the passenger side due to the OBX headers..

Thnx....

[G8nightman]

Nice glad you resolved the issue.


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[XfireZ51]

What did the O2 sensir look like when u took it out?
BTW, I have a spare extension that I had previously used. If u want it, pm me.