Fault code 1.1 H74 , stalling and no restart.?

C4 John

C4 John

CCCUK Member
Hi
Can anyone help got code in section 1.1 H74 as to what this means ?
This is first time shown this code up till now no codes showing with the stalling issues.
I'm also having restart issues , after getting car out of garage turning it off go to restart no go ! This is after about a minute.
Also has been stalling after about or 3 to 4 miles if I go out stalled same place now 3 times ! as if ignition turned off with no restart for 1 or 20 min then runs fine for rest trip 40 miles plus .
If started and let idle without touching anything or moving it just cuts out after 10min repeatable 4 times now .
It's now got so I can't take it out as it stalls after 10min or after turning it off to close garage and will not start for 3 plus hours.
Put new coil ,ignition control module, idle air control module, temp control sensor on .
Security light goes out ok when ignition turned on.
No spark between coil and optispark when not starting .
Always starts from cold so far then cuts out 10 min later or after turned off then No restart.
Runs and revs fine when running idle good , stumbles a bit sometimes just prior to stalling, and once had tachometer go up down then just stalled .
Turns over fine battery New last year .
Now got to point starts from cold turn off leave 1min no restart throws code section 1.1 H74
Any ideas on this problem?
John
 
teamzr1

teamzr1

Supporting vendor
Be more helpful if you state what model and year your Corvette is

Also, how did you obtain the code, jumpered the diag port or with an OBD1 code reader ?
As code does not look correct
 
teamzr1

teamzr1

Supporting vendor
You're correct Steven, must have jumpered the diag port
So would not cause an engine problem
still need to know the year model as if OBD1 or II (for 1994-96, NON ZR1s)
 
C4 John

C4 John

CCCUK Member
My bad sorry .
1993 c4 Aniverssary edition
Got code via jumpered the diag port .obd1 port
H74 code in main screen 1.1 came in bottom screen small numbers cleared it then by push buttons next to screen .
 
teamzr1

teamzr1

Supporting vendor
Hard to follow when text is one big paragraph, so I broke it up

Can anyone help got code in section 1.1 H74 as to what this means ?
This is first time shown this code, up till now no codes showing with the stalling issues.

I'm also having restart issues , after getting car out of garage turning it off go to restart no go ! This is after about a minute.
Also has been stalling after about or 3 to 4 miles if I go out stalled same place now 3 times ! as if ignition turned off with no restart for 1 or 20 min then runs fine for rest trip 40 miles plus .

If started and let idle without touching anything or moving it just cuts out after 10min repeatable 4 times now .
It's now got so I can't take it out as it stalls after 10min or after turning it off to close garage and will not start for 3 plus hours.

Put new coil ,ignition control module, idle air control module, temp control sensor on .
Security light goes out ok when ignition turned on.
No spark between coil and optispark when not starting.

Always starts from cold so far then cuts out 10 min later or after turned off then No restart.
Runs and revs fine when running idle good, stumbles a bit sometimes just prior to stalling, and once had tachometer go up down then just stalled .

Turns over fine battery New last year .
Now got to point starts from cold turn off leave 1 min no restart throws code section 1.1 H74
Any ideas on this problem?
------------------------------------------

So sounds like the problem begins once the coolant temp comes up
If so below like 140F deg coolant, the ECM would be in Open Loop
It would ignore all the engines feedback sensors and runs off of GM's default settings

Once coolant comes up and ECM goes into Closed Loop then it switches over and adjust as what the sensors are reporting
This would be a lot easier to debug if you used an OBD1 scanner (not just a code reader)
Will not restart until the coolant temps comes down again
Test, when problem happens what does the coolant temp show and if leaving the hood open to cool down faster does it start again sooner ?

Using a fuel pressure tester connected to the test port on the fuel rail, see if the pressure from cold to hot stays around 43 PSI
as if getting lower could be a degraded fuel regulator or fuel pump

How many miles on the car, when last time cleaning the throttlebody and fuel injectors ?
 
teamzr1

teamzr1

Supporting vendor
Do you have a 1993 C4 service manual ?
If not I have one as a PDF, but it is 60 megbytes in size so too large to attach to a post here

Would your email server deliver to you that big of an email,
If not I could put it on my Internet server, and you download it from there
 
Last edited:
C4 John

C4 John

CCCUK Member
Thank you TeamZr-1
Will get back about temps have written some down .

Trying to source someone with obd1 reader , have asked 4 local garages and 3 auto electricians no joy.

Will get local garage to pressure test fuel rail will need to book it in.

Milage 99773.
Don't know when throttle body last cleaned. Looks clean when I removed air intake.
had new optispark plugs and leads water pump and some new injectors not sure how many and why thy didn't do all of them 10k miles ago .

This eve Started it was at 81F not clean start stumbled a bit idle settled bit lumpy revs ok.
Turned off @99F did start straight away then walked to house and back would not restart .
1hr 15 min later @ 88F still no start.
 
teamzr1

teamzr1

Supporting vendor
C4 John said:
Thank you TeamZr-1
Will get back about temps have written some down .

Trying to source someone with obd1 reader , have asked 4 local garages and 3 auto electricians no joy.

Will get local garage to pressure test fuel rail will need to book it in.

Milage 99773.
Don't know when throttle body last cleaned. Looks clean when I removed air intake.
had new optispark plugs and leads water pump and some new injectors not sure how many and why thy didn't do all of them 10k miles ago .

This eve Started it was at 81F not clean start stumbled a bit idle settled bit lumpy revs ok.
Turned off @99F did start straight away then walked to house and back would not restart .
1hr 15 min later @ 88F still no start.
Click to expand...

So low temps, less than 100F degs and still runs crappy
So does not sound like a heat issue or a issue with the ECM degraded due to heat
If optispark was an issue, engine would start and run but not well all the time and being you swapped it
and still a problem it is not the issue

when was the last time the fuel filter was replaced ?
Get that fuel pressure checked from cold to normal coolant temps, again should stay around 43 PSI at fuel rail

Have you looked for any air leaks, like vacuum or PCV hoses ?
Could have gotten a bad tank of gas ?
 
C4 John

C4 John

CCCUK Member
Yes I have part one service manual not the electrical part .

Vacuum leaks have replaced flexible hoses.
cruise control, ABS/ASR all work fine , fuel pressure vacuum line hisses well when removed and engine running.

bad fuel dont know im now on 4th tank in last couple months and have put some redex through.

The cutting out has gone from occasionally to grrrrr every time or won't even start now .

Managed to borrow fuel pressure tester from local garage (thank you Simon )

Please say if I'm doing anything wrong as this is all new to me.

Pressure test
Turn key to run fuel reading psi@ 46 then dropped back almost immediately to 43psi .
Turn key to off
waited 2min fuel reading psi@ 42.5
Waited 4min psi@ 42.5
Waited 6min psi@ 42
Waited 8min psi@ 42
Waited 10min psi@ 41

Cleared tester, repeated almost same result.

Cleared repeated same results.

Cleared turned to run again psi@46 dropped almost immediately to 43psi Turn off
Left for an hour psi@38.

Next test. Run engine.

Turn key to run temp 78F fuel reading psi@43 no start ! 4th attempt started no hesitation.

Tester reading fuel psi@ 34 to 37 at idle

Pulled vacuum pipe off fuel pressure regulator fuel psi went up to 46psi hissing from vacuum pipe reattached fuel psi back down to 35 to 36psi

5min later @122F held revs @ 2000 fuel psi@36. Steady.

Waited at idle for 2min now temp 131F went to increase revs cut out like Turn key off fuel psi @45.
Would not restart fuel pressure still @ 43 no codes.

Ecm hot put ice blocks on for 10 min started engine no problem engine temp 122F , will need now to repeat this .

Engine idle good fuel pressure reading psi@36 to 37

Revs up to 2000 holding fuel psi@ 35 steady.
Temp 151F

Back to idle fuel psi@ 36to 37
temp 174F

Revs back up 2000 and over back to 1500 fuel psi@ 35
temp190F

Put in gear 850 Revs Fuel psi@ 37
temp 196F

Turned off restart no prob repeated. Twice.

Letf for an hr
Fuel reading psi@12?

Started ok same fuel reading psi@ 46 dropped to 43 started revs ok idle psi@36to 37.
Temp160F.

Left for another 1hr
Fuel reading from psi@ 44 to psi@7 in an hr ,,is this dropping to quick?
Engine temp now 139F no start.!
Fuel pressure as per normal back up psi@46 then drop back to 43 but no start.
Ice blocks on ecm for 10min no diff no start.

But fuel reading psi @37 so has dropped from 44 to 37 in 10 min
Engine temp 132F

That's it for now !!
Thanks for your patience and looking .
John
 
teamzr1

teamzr1

Supporting vendor
Sure sounds like the fuel regulator is degraded or vacuum to it
Not sure in your case but many times if pulling the vacuum hose off regulator and gas come out
is a sign of internal damage

No reason, fuel rail pressure dropping but a few PSI from 43 PSI
and rail pressure should hold for some time, but not sure how long ?
I asked, but possible a mostly clogged fuel filter will allow the pressure but very little gas volume

I asked about service manual as it would have a debug process to determine this problem
 
teamzr1

teamzr1

Supporting vendor
As I mentioned, this would be rather Easy if you bought or borrowed a real OBD1 scanner
More

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