Wait to start light slow to come on

[buzzman]

For the past couple months the wait to start light is slow to come on for the 1998.5 truck my signature. The lift pump is also slow to cycle on and off at the same time. I wait about 5 to 10 seconds and light comes on and the pump cycles and the motor starts and runs fine. Sometimes the light and pump work just fine with no delay.

I always do my own work on this truck and have been able to figure out how to fix everything from the information I fine on this forum. But with this problem, I'm not sure what is going on. The batteries are just over one year old. I have pulled the plugs on both computers (block mounted and firewall mounted) and cleaned the terminals with electrical cleaner. I have checked all the grounds I could find. The motor is stock and has always run well.

Is one or both of the ECM/PCM computers going bad? I don't know which of the computers control this start sequence, the one on the side of the block or the one on the firewall? Any recommendations? Do I need to buy a new computer? Can I just get the computers re-flashed?

Thanks,
Buzz

 

[GAmes]

If it was a 12 valve I would first look at the intake air temp (IAT) sensor. Test specs I believe are in the FSM. There could be a troubleshooting procedure in there as well. Also, the FSM has theory of operation info that would tell you which module controls the WTS light and the lift pump. I doubt very much that you can get a reflash, or ever could.

 

[buzzman]

Does anyone know which computer controls the WTS light and fuel pump bump?

 

[DavidC]

Fuel pump is ECM, probably the WTS light also which is triggered by the Intake Air sensor

 

[Mike B.]

I hate to be the bearer of bad news but that's a classic symptom of a failing ECM. In my experience the symptoms being after a hot engine is shut off and restarted after 5-10 minutes of heat soaking. As the ECM continues to degrade the hard starting gets worse. For me a key indicator is that the lift pump will not run UNTIL you see the wait to start light come on. The engine will crank just fine but it won't fire off until the WTS light & lift pump run.

Search the forum for my old posts on the topic and you'll find the company I sent my ECM's to for repair. Sadly our ECM's have been out of production for at least 8 yrs now so no new old stock will be found, at least not easily.

Cheers
Mike

 

[Mike B.]

Found the link for you! https://www.automodulesource.com/

 

[KATOOM]

For the past couple months the wait to start light is slow to come on for the 1998.5 truck my signature. The lift pump is also slow to cycle on and off at the same time. I wait about 5 to 10 seconds and light comes on and the pump cycles and the motor starts and runs fine. Sometimes the light and pump work just fine with no delay.

I always do my own work on this truck and have been able to figure out how to fix everything from the information I fine on this forum. But with this problem, I'm not sure what is going on. The batteries are just over one year old. I have pulled the plugs on both computers (block mounted and firewall mounted) and cleaned the terminals with electrical cleaner. I have checked all the grounds I could find. The motor is stock and has always run well.

Is one or both of the ECM/PCM computers going bad? I don't know which of the computers control this start sequence, the one on the side of the block or the one on the firewall? Any recommendations? Do I need to buy a new computer? Can I just get the computers re-flashed?

Thanks,
Buzz

How long have you had your truck? Is this something new or something you've just never really noticed and are wondering if its normal? I ask because there are parameters which the diagnostic system uses to determine how long the WTS light comes on for and if the lift pump needs to cycle.

 

[Mike B.]

A properly operating ECM should send fuel to fire the engine regardless of the WTS light status. One key point in this diagnosis is how the engine starts HOT after being allowed to heat soak the ECM. Not that it couldn't be something else but in my experience with owning two 2nd gen trucks over 20 yrs & close to a million miles combined leads me to confidently say Buzzman needs an ECM.

 

[buzzman]

Thanks to all for your comments and suggestions. I got this truck in 2011 with about 107K miles on it. It now has 218K miles. It has been well cared for and has had a relatively easy life. The motor has always run well and still does run well. This WTS light/fuel pump delay problem started this past January. As everyone has said, the motor will not start until that WTS light comes on and the fuel pump cycles. Once it starts, everything runs fine. I suppose I will eventually need a new ECM.

However, I may have fixed the issue, at least temporarily. I do know the electrical system in these trucks is very sensitive to poor grounds, electrical interference from the alternator, weak batteries, etc, etc. I checked the grounds, and my batteries are only one year old. I also unplugged the big electrical plug that goes into the ECM to make sure it wasn't corroded. It all looked good to me. So I thought a new alternator would be worth a try. Last week I purchased a new alternator on ebay ($125) and installed it. And now the WTS light and fuel pump are working fine. Happy, happy! It may be only a temporary fix, we'll see. I will report back on this fix after I give it more time.

I'm also in the process of replacing all the battery cables and battery clamps. They are 21 years old and starting to show their age.

Thanks again,
Buzz

 

[KATOOM]

Did you test the AC noise levels on the old alternator? And you should test them on the eBay one too... Just because its new (or likely rebuilt) that those levels will be within spec. The best alternator configuration today is hairpin wiring and 12 diodes instead of 6.

 

[buzzman]

Yesterday I plugged in my scan tool and got a P0122 code (APPS/TPS low voltage). Is that caused by a bad ECM? The WTS light delay problem has returned too. I looks like I will be installing a new ECM.

 

[Joe Mc]

Buzz, a few years back I almost went the route of changing the battery cables, due to the clamp at the battery(s) terminal ends being almost fully cracked. I decided to give these https://www.genosgarage.com/product/ubt-840n/Electrical-accessories a try, they come in black and red and are a heck of a lot less expensive than new cables. For me they did the trick and provided a better connection point for accessories than the stock terminal ends.

 

[buzzman]

Joe Mc, thanks. I did look at the Geno's replacement battery cable kit, and it looked like a good way to go, however I decided to make my own. I had the proper cable crimp tool and some cable ends already. While I was at it, I replaced the smaller ground wires too. I used military style battery clamps and I think the Geno's kit uses them also.

 

[Jetson]

Disconnecting the batteries will sometimes correct the delayed wait to start for a while, but the ECM is still going bad.

 

[buzzman]

I ended up sending my ECM to Auto Computer Specialists to be rebuilt. Cost $250, about 12 days to get it back. It seems to be working okay now.