Ready to Run, but Won't Start

Wondering if anyone has run into this problem...

Engine cranks, tries to start, and can't. It's actually fired up a couple times and ran for a couple seconds, then died. It will run if I repeatedly spray starting fluid in it. It's got good fuel pressure in the rail (55 psi). I pulled the rail off and stuck the injectors in 8 dixie cups. When I crank it, they puff out fuel once, then no more.

I saw this post on ls1tech that sounds exactly like my problem (944 with ls6, though), but noone had any answers for him:
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Any help would be greatly appreciated!

Here is some info about my setup:
2000 ls1 with 24k miles
99 f-body harness
2000 pcm, tuned for my setup
28# injectors
street & performance modified fuel rail for return line setup
pcm fuel pump signal wired into 944 DME relay (switched pos and ground to trigger from pcm +12V signal)
pcm wires for injectors, coils, MAF, etc wired directly to battery positive terminal (temporarily until I get it running)
oem MAF and MAP sensors
oem coils
new NGK TR6 plugs
oem plug wires
bosch O2 sensors (for 99 f-body)
99 f-body idle valve and TPS
ls6 intake, valley cover
mild cam, beehive springs
modded S&P headers
ported throttle body, relocated to end of custom 90 elbow tube
no radiator hoses or coolant yet (waiting til I get it running)

The ECU grounds the injectors thus opening them. The problem seems to be in your wiring. Injector wiring needs to be to the ECU for grounding per cam sensor signal. If you have a VATS module, the ground for the fuel pump needs to be to a chassis ground and not to the ECU.

from my searching for various no start problems, i have a feeling you might have a problem with vats...i've read that if the vats module is still active or has an issue (tuned out but not really?) the car will start and die quickly, this might explain your single spray from the injectors and then nothing....also check your power wires and grounds related to the injectors...i had an issue with a looped power wire that couldn't get ground from the pcm on my lt1, could be something similar on yours.

Good luck!
Ethan

Thanks 944-LT1 and Ethan. I will double check the wiring. My harness was put together by a pro (Jim's Performance in MD), so I doubt that is an issue, but will check anyway. The wires I mentioned hooking up to constant +12V (rather than switched) are the ones that supply power to the PCM, for the injectors and coils.

One thing, I don't think should be an issue, but I have the harness grounded to the driver side head, and the battery ground going to the passenger side head. Any problem with that?

vt951 wrote:pcm wires for injectors, coils, MAF, etc wired directly to battery positive terminal (temporarily until I get it running)

Alan,

944-LT1 is right. The pulse signal comes from the PCM. Connected directly to battery [+] will fire the injectors once. The DME / or fuel pump relay (if not using the Porsche DME relay) is probably the problem. Use the connections Tom specified, and the DME relay will work. Or, check here...

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The computer has been flashed hasn't it? No vats? Even with vats still programmed, it should run. Ground the block to the body somewhere. The solid mounts should do it, but a dedicated ground can't hurt.

Your headers are here also, but I doubt I can get them there before Friday...

Greg,

Just to clarify, I don't have the injectors wired directly to +12V. I have the PCM wired directly to +12V, rather than switched power.

Thanks

This sound just like the problem I had, only mine would run for 10 to 20 seconds. I pulled my hair out trying to figure out what the problem was, checking and rechecking wiring, engine sensors, etc. Found out it was the VATS Eliminator Module I bought from 3rdbrakeflasher.com. It was not producing a high enough voltage for the PCM to register it. So even though it was producing the 50 hz square wave signal that the PCM was looking for, the amplitude of the signal was too low. I fixed the problem by building my own for about $5 in parts from Radio Shack. It is based on the very common 8-pin integrated circuit known as the 555 timer. I followed the picture below that I found somewhere on the net. Just connect the grounds, take the +5 VDC power from pin C230-A (blue 10-pin connector on engine harness) and connect the output to the PCM via C230-E. It worked like a charm. Incidentally, 3rdbrakeflasher did make good on their bad VATS module and sent me a good one promptly.[You must be registered and logged in to see this image.]

Thanks Bridar. I'm curious why you would have to use an external device to disable VATS. Can't it be done through tuning software directly in the PCM?

The VATS Eliminator Module is not required, it is simply a short term substitution for having the PCM reporgrammed. I wanted to be sure everything else was right on the car before I had the programming done. Other than having the annoying Check Engine light and the "!" light on, not reprogramming the PCM does not make any difference. If you have many engine modifications, you will eventually have to have the PCM reprogrammed to optimize the power output. Mine runs fine without the programming and allows me to forstall the $250 to $300 to have the reprogramming done properly. An added benefit of using the VATS Eliminator Module is that you can use it as an added security device if theft is a concern. You can wire it as a plug in device and just take it with you as you would the car key. The car cannot be driven away without it.

I know as hot-rodders or home-wrenchers or what ever we want to call ourselves, we as a group like to do everything at once and put all the shiney parts and features in at one time. But my philosophy has been to get the beast driving first, then worry about the nice-to-have options. After all, project cars are NEVER finished, they only get resold!

I sent the PCM out to the programmer, and just found out yesterday that VATS was in fact disabled, so it is not the cause of my no-start issue. Next step will be to check all injector related wires in the harness. Unfortunately, I am out of town until next week, so it will have to wait.

Hey there - I see a brief reference to your harness being grounded to the heads. Do you have your battery grounded to the engine? I think I remember having an issue with grounding the engine (and not just 16 gauge - get the thick stuff!)

Skywalker,

I have the battery ground (stock 944 cable) bolted to the passenger side head, and the harness ground lug bolted to the driver side head. I thought maybe that could be an issue, because there must be some resistance between the two heads. However, when I mentioned that to a few people, they said that shouldn't be a problem, so I left if alone. Now, you've got me thinking I should tie them together.

Alan

*****pcm fuel pump signal wired into 944 DME relay (switched pos and ground to trigger from pcm +12V signal)*****

Can you expound on this? Where did you hook up the LS1 PCM Fuel PUMP signal wire to exactly? Terminal 86 on the DME relay comes from the disable circuit on the alarm.....

xschop,

I have the exact pins/wires that I cut and spliced written down, but don't have them with me right now. I will post that info up here later.

In any case, the fuel pump is operating correctly from what I can tell. Fuel rail is pressurized to 55 psi, but still the engine won't run. That's why I think it is a problem with the injectors or the electrical signals to the injectors.

Thanks,
Alan

The easiest way to see if the injectors are firing is to pick up a set of "Noid lights" at the local autoparts store. Autozone or Advance will have them to borrow. Basically the light just plugs in where one of the injectors would be on the harness. Pulll thte plugs wires on each cylinder to disable the ignition and then crank the engine and if the light lights, you know it is not the injector wiring.

I took some time to draw a schematic of how I am bypassing the Entire Porsche DME/Fuel pump relay (G5) and install all new aftermarket relays... Even If your alarm control box decides to go south.....the Porsche DME relay will not operate....... I'm doing it with 2 separate fuse blocks and 4 total relays..... The key for me was to tap into fuse #36 which is 12v+ constant throughout entire keystroke including starter ignition.....And Fuse #34 is being bypassed straight to the fuel pump from a new relay.....I will try to get a nice MS paint drawing up shortly.... Only thing I have left is hunting down the "CEL" wire in the dash and see if it comes to the fuse box to make it 100% plug/n/play....

Im not sure how it works on mine. I have a stand alone harness from speartech, which came with a fuse and relay block just for the fuel pump. When I had the last few wires installed at the shop they hooked the fuel wire straight to the fuel pump. All the stock fuel harness was bypassed then.

Why can't that work for you guys?

After a few chats with Eric (ADMIN) I don't want anything to do with the Factory DME relay, pin #86 ties into the alarm via a diode.....one more problem to worry about
Here's what I'll be doing this weekend...
I double checked the switch positions and if your key switch is really worn, there will be a few milliseconds of no contact (according to my voltmeter)... This may be tripping up some of you running the factory DME relay.... I will re-post the exact side of each fuse to jump off from.....Fuse #36 has to be jumped opposite the radio wire side because if your radio fuse blows...your new PCM relay will shut down....Fuse #34 has to be jumped the side of the 944 factory Green/Blk wire that goes directly to the fuel pump

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after looking at that wiring diagram there are two thing i think should be changed for saftey. Both of the 86 feeds for the fan wires should be fused, they are just control side so they could be fused together just fine. I would also install a mega fuse at the positive battery connection. You can get the base and fuse for like $20 or less from McMaster carr.

Mark

SSP told me that the leads from the fans did not need to be fused nor the fuel pump lead. If I did what size? 3 amp or 5 amp?

I am using 2 seperate blocks, 1 switched and one hot that will be located on opposite sides near the firewall. The fan side and relays I am putting on the driver's side, the pcm relay on the passenger side. I have the silicone drying tonite and willl wire it all in the morning....

Hey XS, I wasnt referring to the leads that go to the fan, they are covered by the fuses going supplying to terminal 30. I was referring to the leads that junction to the feed for the fusebox and go to terminal 86 of the relay, positive side of the control circuit. Those two circuits are direct feeds from the battery and not fused anywhere. Honestly those 2 circuits require less than 1 Amp to operate, so a 3 Amp fuse would be more than sufficient. The Maxi fuse at the battery would be a little different, I got a slow-blo Maxi fuse rated for 150Amps, itll allow up to 1000 amps for like 30 seconds before blowing i believe.

HTH

Mark

Ah O.K. I see....I finished the wiring yesterday....and incorporated your suggested safety net on the key switch and fuel pump relay....

I also disconnected the Green/blk hot wire directly at the rear fuel pump with a long wire lead to read continuity of the circuit....confirmed that it goes and connects to DRIVER'S SIDE of FUSE #34....So as I suspected, you either remove fuse #34 and use a single spade to jump it OR the Green/Blk wire at the 14-pin connector ties in under the fuse panel (which is what I did)...

For the new PCM relay, I simply added a jumper connector (ON DRIVERS'S SIDE)....

The fans were easy. Just tied in to the large RED/blk and Black/red wires in the loom right next to the driver's side strut tower.....
.................No More Porsche DME/Fuel pump relay or Fan relays........Happy Independence Day!

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How many amps where the relays you used?

3 relays from SSP were 50A IIRC. Same for the fuel pump relay I got from Pimp Boys...
I used 8 gauge for the Battery (+) wires to blocks and 12 gauge for the fan mains......The old Fan wires that I tied into near the tower were shiney copper and I re-used them. I shot the fan connectors out with carb cleaner and put some dielectric Si. grease and replugged them......
Big Thanks to Eric (Admin) for his help with relay knowledge....

The only thing I was worried about was if the car had an alarm module from factory and the P.O. had removed it, because it is not in the passenger footwell like found here....

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