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Lean run N42 stock EFI


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Hi there folks,

L28 with N42 head and block and stock EFI getting really rough warm up idle.  Car fires right p but then rough until very warm.  What helps greatly is if I unplug the vaccum hose from the FPR (also stock) which increases the fuel pressure to 40 psi. Then the car warms up without cutoff. 

 

Any ideas ? 

 

Ive tested all the connections per the Z fuel injection bible and everything checks out except the AFM which is slightly off.  

 

Ive checked fo vacuum leaks with smoke test and fixed two. Still same issue. 

 

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On 8/11/2019 at 5:09 PM, ZHoob2004 said:

Have you actually measured fuel pressure? I had a similar issue with running lean and it turned out to be restriction on the fuel pump inlet caused by an inline pre-filter. Removing that immediately fixed the lean issue.

Hi, well, I have a fuel pressure gauge in between my fuel filter (stock one) and the fuel rail input...seems to be working well.  It measures appx 26 with car running but during warm up this is not enough, it wants to cut off unless I unplug the vac from the fpr and then the pressure goes to 40... 

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According to my 77 factory service manual (you can download this, check google), the fuel pressure is supposed to be 36.3psi relative to your intake manifold.

 

Subtract the approximately 10psi of vacuum you should have at idle (~20in hg estimated), that gives you the 26 you're reading on the gauge.

 

I think your fuel pressure is working just fine and your problem is elsewhere and raising the fuel pressure is simply masking the real issue.

 

Have your injectors ever been serviced, and have you checked that they aren't clogged?

 

 

EDIT: Have you checked your cold start valve/system? It has basically the same function as a temperature-controlled choke, but instead of restricting air it just adds extra fuel to the intake manifold while cold.

Edited by ZHoob2004
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  • 1 month later...
On 8/14/2019 at 6:38 PM, ZHoob2004 said:

According to my 77 factory service manual (you can download this, check google), the fuel pressure is supposed to be 36.3psi relative to your intake manifold.

 

Subtract the approximately 10psi of vacuum you should have at idle (~20in hg estimated), that gives you the 26 you're reading on the gauge.

 

I think your fuel pressure is working just fine and your problem is elsewhere and raising the fuel pressure is simply masking the real issue.

 

Have your injectors ever been serviced, and have you checked that they aren't clogged?

 

 

EDIT: Have you checked your cold start valve/system? It has basically the same function as a temperature-controlled choke, but instead of restricting air it just adds extra fuel to the intake manifold while cold.

Thanks, issue still going on running rough.  I think my injectors have sediment again :(   This am I pulled off the cold start and black sediment was in the fuel that I caught in a small plastic container.  May pull the whole rail again and clean injectors, replace fuel filter, etc.... that rail is a pain so may just upgrade to a straight one. 

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  • 1 month later...

Removed the rail and tested injectors with a 9 volt battery and carb cleaner. 3 work, 2 clogged and 1 dead!  Car has been running off 3 injectors!  Ordering new ones and a new fuel rail and FPR right now !  Rock auto has new or rebuilt beck arnley N/a injectors anyone have any thoughts on those ?

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