EFI Help *SOLVED*

[MTMike]

My truck has one of the horrible Holly Pro-Jection 4D systems in it, and as you would expect the thing is very finicky. It hates to run when it's cold (below 40)... until it's up to full op. temp I have to restart it. If it's warmer out, it has no problems

Well tonight it's about 5 degrees out and I got it started, got it warmed up, and drive it around the block a few times to test it out. It ran and drove fine, except it wouldn't ever really idle - it was hovering around 1200rpms in gear with no load, but it's always done that and the engine has a pretty hot cam.

I got back into the driveway and decided to back out again to test one more thing and as soon as I put it into Reverse, it stalled. As soon as I restart it and put it back into reverse it stalls again. If I get it into reverse with some throttle while holding the brake, it would try to stall out like it wasn't getting fuel for 1 second, fire up to ~2000rpms for 1 second, try to stall for 1 sec, and do this for 5-6 seconds and before it all-out stalled. It just seemed like the load of it in reverse was just enough to lower the RPMs enough to change something in the computer that set it into a "run" mode that it couldn't handle at only 5 degrees. My mechanic friend suspects the intake charge temperature sensor or the coolant temp sensor.

Does anybody else have any experience with this horrible EFI system?

Thanks!

 

[4X4HIGH]

I don't know how complete a system those are but i was going to suggest both the ECM temp sensor and or the air temp sensor. I think your friend is looking in the right direction for you.

 

[southernspeed]

If that was a stock TBI system I'd suggest the reverse/stall problem is to do with the wiring from the nuetral/park sensor. Maybe going into reverse is still indicating park so the ECM isn't ready for load.
Just a thought!

 

[MTMike]

If that was a stock TBI system I'd suggest the reverse/stall problem is to do with the wiring from the nuetral/park sensor. Maybe going into reverse is still indicating park so the ECM isn't ready for load.
Just a thought!

Thats what I was thinking, but this truck was so highly customized by the previous owner, it doesn't have a starter-block switch - meaning I can start it in any gear including reverse. The Holley system isn't nearly as "smart" as a GM TBI system - it's got 5 sensors and thats all. A Coolant Temp, an Air Charge Temp, TPS, a MAP, and an O2.

 

[southernspeed]

That's really weird, I guess it must sense load just by the MAP sensor. Seems very primitive though. Even that said, I can't see why it would only do that in reverse. Have you been on to Holley about it?

 

[MTMike]

That's really weird, I guess it must sense load just by the MAP sensor. Seems very primitive though. Even that said, I can't see why it would only do that in reverse. Have you been on to Holley about it?

Yeah, thats what was confusing the crap out of me too. The only thing I can think is that maybe Reverse put a stronger load on it and brought the loaded rpms down just enough to kick the Holley ECM into a different mode that it wasn't doing in forward gears. Being it was like 5 degrees, that other mode which relies more heavily on one of the temp sensors, which if one was faulty, it would stall out, or try to stall out with the on/off effect I was seeing.

I'll have to give Holley a call and see what they say. I have a trail ride in the snow this Sunday so lets hope I don't have to back up

 

[MTMike]

I just talked to a tech at Holley and he thinks it could be too low of fuel pressure causing it to run too lean in the cold air, and also the open element filter isn't helping the cause with cold air. He suggested I look into getting a stock-style filter housing w/ the manifold heating tube (or whatever those things are called) and also suggested I check my fuel pressure. I'm not sure how to go about that with headers but what about running the air intake hose into the cab?

Does anybody have a stock snorkel style air cleaner housing they wanna give me instead of throw away? (I'll pay shipping)

 

[southernspeed]

Still can't see why reverse would be different? Keep us posted!

 

[BadDog]

That's what I was going to say, but looks like I found it too late to help. My GM TBI acted a lot like that (though not cold weather related) not long after I installed it. Turned out the rubber line between the pump and hard line had ruptured and fuel pressure was way low due to the bleed back into the tank.

When dealing with fuel injection, any time you have a problem that is not just blatently obvious where the problem is, or if the seemingly obvious checks ok, check the fuel pressure first. If you don't know the pressure is good, further investigation is really pretty pointless...

I also agree on the breather. My K5 had a fancy "Air Aid" snorkle with K&N cone on the end when I got it, and it really *sucked* until it warmed up, even in Phoenix winter weather (still above freezing). I put the stock breather off my truggy on it along with the heat tube and it ran SOOOO much better right away.

 

[dyeager535]

Air intake hose is to provide warm engine air under cold operating conditions, specifically warmup, but not exclusively.

Putting it in the cab would be pointless for cold engine operation obviously.

Some headers are made with the fitting welded on them, (edelbrock TES?) I'd be surprised if SOMEONE doesn't make a bolt on piece.

 

[MTMike]

I got it figured out. Turns out that the electrical connector to the "TACH" pin on the Distributor was loose and breaking the connection when in reverse. I noticed my tach was being wierd.

Come to find out, the ProJection system requires a tach signal, otherwise it cuts off fuel, so as soon as it lost the tach signal, it'd cut fuel and stall.

It's weird that only putting the truck into reverse would cause the connection to break, but apparently thats what was happening.

I fixed the connection and it runs as good as can be, even in the 10 degree weather we've been having today.

Thanks to all for your help!