Snapping, popping when cold. Fuel pressure?

Y

Yarko

Registered
LocationOntario Canada
Hey everyone. My situation is not as common as some but I'll fill you in. I have a 95 Mark viii motor and trans in my 1967 f100. I used the factory computer and wiring. I'm using a walbro gss342 (I believe). 255lph pump with a fuel cell. Truck ran great. I notice though that if the truck is cold, towards fall, it will spit and snap and sound harsh at first. A couple minutes down the road and it seems to clear up. I have had issues under hard acceleration where it will stumble. It has all new 02's. Maf sensor cleaned, new temp senders etc. I tested fuel pressure yesterday and it was 32 at idle and 41 with the regulator unplugged. I'm finding differing info for the fuel pressure at idle and revving. Can anyone steer me in the right direction? Thanks!
 
Hi Yarko,I have a 96 mark viii.I upgraded the fuel pump and installed a fuel pressure gauge since I run a 125 shot of nitrous.At idle the gauge reads 30 psi,under acceleration it jumps to 40 psi.Hope this helps.
 
The service manual states the specification for Engine Running fuel pressure is 30 psi to 45 psi. The Key On / Engine Off fuel pressure specification is 35 psi to 45 psi.
 
At a glance, those pressures look good.

Any chance you bought cheapo generic 02 sensors? I made that mistake once......

Also. Cool truck!
 
jyarosz said:
Hi Yarko,I have a 96 mark viii.I upgraded the fuel pump and installed a fuel pressure gauge since I run a 125 shot of nitrous.At idle the gauge reads 30 psi,under acceleration it jumps to 40 psi.Hope this helps.
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It does! Thanks!!
 
tixer said:
At a glance, those pressures look good.

Any chance you bought cheapo generic 02 sensors? I made that mistake once......

Also. Cool truck!
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That's a good question. I did change the o2's but I was having the issue before as well. I haven't noticed any difference since swapping them. If have to look back a bit to see which ones they are.
 
driller said:
The service manual states the specification for Engine Running fuel pressure is 30 psi to 45 psi. The Key On / Engine Off fuel pressure specification is 35 psi to 45 psi.
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So at first glance my pressures seem good. I didn't however try it key on/engine off. I'll have to try that when I get out there again.
 
Yarko said:
LocationOntario Canada
...I notice though that if the truck is cold, towards fall, it will spit and snap and sound harsh at first. A couple minutes down the road and it seems to clear up. I have had issues under hard acceleration where it will stumble....
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I hate speculating on things of this nature, but I have to wonder if your symptoms are related to the EVAP system, or perhaps in your case, the lack of an EVAP system?

If it were mine, I would try to datalog the events and compare the cold, spit and snap running to the more normal running. That in itself would not give you the answer, but should at least give you a direction to start looking. Think in terms of Fuel, Air and Spark.
 
billcu said:
Are you using the original MAF sensor?
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Yes. Original MAF. I've cleaned it really well (what I thought was good) and it may have been a but better. I was leaning to that as well but I thought I'd clean it first. They aren't cheap! Lol.
 
driller said:
I hate speculating on things of this nature, but I have to wonder if your symptoms are related to the EVAP system, or perhaps in your case, the lack of an EVAP system?

If it were mine, I would try to datalog the events and compare the cold, spit and snap running to the more normal running. That in itself would not give you the answer, but should at least give you a direction to start looking. Think in terms of Fuel, Air and Spark.
Click to expand...
 
It's definitely cold/cool weather related. It is even "cold engine" related. I notice it most in fall temps but I believe it even does it if I fire it up to go home for lunch on a nice day. I deleted the egr as well. Not sure if that matters.
 
Also. A mechanic friend of mine mentioned a vacuum leak. If the engine is cold it may suck excess air through a gasket. I fired it up cold and sprayed break cleaner all over the engine. I sprayed intake, vacuum lines, you name it, and had zero surge. So I don't think I have an obvious vacuum leak.
 
The fuel/air/spark parameters are significantly different with a cold start. The air fuel ratios are generally rich when first started, so anything that would cause more fuel to be added would only aggravate the problem. I would be curious what the short term fuel trim numbers were cold versus normal along with IAT and ECT readings.

You mentioned the EGR was deleted, what about EVAP system? Secondary AIR system?

Are you running with the stock tune or a custom tune?
 
driller said:
The fuel/air/spark parameters are significantly different with a cold start. The air fuel ratios are generally rich when first started, so anything that would cause more fuel to be added would only aggravate the problem. I would be curious what the short term fuel trim numbers were cold versus normal along with IAT and ECT readings.

You mentioned the EGR was deleted, what about EVAP system? Secondary AIR system?

Are you running with the stock tune or a custom tune?
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The evap system was deleted alsoi believe. Basically running the engine and trans only. I have a factory tune as well. I was wondering.. Would the air charge temp sensor be a part of it? I know it controls fuel also. Other than the MAF sensor, it's the only one I haven't changed.
 
Yarko said:
Would the air charge temp sensor be a part of it?
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IAT... Intake Air Temperature sensor... a.k.a. air charge temp sensor is indeed a part of it.

The reason I was asking about EVAP and others is it may very well be an 'open loop' versus 'closed loop' reaction which can be perceived as a temperature related symptom. Closed loop is in play once the engine reaches operating temperature and other parameters are met... prior to that the engine is operating in open loop and ignoring certain sensors/systems. It's not so much a cause than an effect... especially with the factory tune.

With the factory tune on a 'modified' setup, the PCM is commanding certain systems, EVAP, EGR, Secondary AIR, etc... and expecting certain responses and reacting accordingly. If the expected parameter response is 'out of range' for the strategy employed, there is a default response for the air/fuel command as well as timing. There is even Failure Mode Effects Management that could come into play when certain sensors are compromised.

Back to the problem at hand... Specifically the IAT may cause extra fuel when 'cold' and less timing when 'hot'. It is simple enough and cheap enough to replace if there is any question. You can use an OBD2 scan tool to monitor live parameters of several sensors as well as monitor fuel trims which may help in determining what is going on.
 
driller said:
IAT... Intake Air Temperature sensor... a.k.a. air charge temp sensor is indeed a part of it.

The reason I was asking about EVAP and others is it may very well be an 'open loop' versus 'closed loop' reaction which can be perceived as a temperature related symptom. Closed loop is in play once the engine reaches operating temperature and other parameters are met... prior to that the engine is operating in open loop and ignoring certain sensors/systems. It's not so much a cause than an effect... especially with the factory tune.

With the factory tune on a 'modified' setup, the PCM is commanding certain systems, EVAP, EGR, Secondary AIR, etc... and expecting certain responses and reacting accordingly. If the expected parameter response is 'out of range' for the strategy employed, there is a default response for the air/fuel command as well as timing. There is even Failure Mode Effects Management that could come into play when certain sensors are compromised.

Back to the problem at hand... Specifically the IAT may cause extra fuel when 'cold' and less timing when 'hot'. It is simple enough and cheap enough to replace if there is any question. You can use an OBD2 scan tool to monitor live parameters of several sensors as well as monitor fuel trims which may help in determining what is going on.
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Awesome info. Thanks so much! Quick question.. I can use a Obd2 scan tool?
 
Yarko said:
Awesome info. Thanks so much! Quick question.. I can use a Obd2 scan tool?
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Yes, you can use an entry level OBD2 scan tool and view live data. I use one from <link>Innova</link> but there are various manufacturers. Simply plug into the OBD2 port and start scanning.

Just be sure it is not just a code reader... you want to at least be able to read live data. With the '96 being an early OBD2 - you don't need a high end diagnostic tool, anything above a mid-level tool would be overkill. Besides streaming live data, being able to record and graph live data would be a plus.

Before I bought the Innova tool I currently have, I had a simple BlueTooth model that used a phone app. Kind of gimmicky, but it worked(mostly) to display simple data such as engine temps, rpms, battery voltage, etc... not much more than a gauge readout for your phone.
 
driller said:
Yes, you can use an entry level OBD2 scan tool and view live data. I use one from <link>Innova</link> but there are various manufacturers. Simply plug into the OBD2 port and start scanning.

Just be sure it is not just a code reader... you want to at least be able to read live data. With the '96 being an early OBD2 - you don't need a high end diagnostic tool, anything above a mid-level tool would be overkill. Besides streaming live data, being able to record and graph live data would be a plus.

Before I bought the Innova tool I currently have, I had a simple BlueTooth model that used a phone app. Kind of gimmicky, but it worked(mostly) to display simple data such as engine temps, rpms, battery voltage, etc... not much more than a gauge readout for your phone.
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My engine is from a 95 with a obd1 port under the hood. I was planning on buying the innova obd1 scan tool that actually gives codes rather than counting flashes. Sorry if I wasn't clear on that
 
Oh snap! :oops:

Sorry 'bout the confusion on my part. That definitely rules out data logging with a scanner... one of the reasons I had my '93 converted to OBD2.

I'll dig through my archives and see if I can come up with anything to help with the EEC-IV.
 
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