1st TBI Conversion Help Needed

[Dougnsalem]

Well, that kinda sounds like good news to me. H
Be interesting to hear what @1987 GMC Jimmy thinks....

 

[1987 GMC Jimmy]

I think it’s time to get the Mityvac and test the vacuum holding abilities of both the MAP sensor and the booster.

 

[MtBraun]

I think it’s time to get the Mityvac and test the vacuum holding abilities of both the MAP sensor and the booster.

I did test the MAP - all seemed fine. Voltages were slightly (.25 volts) below the referenced voltages, but probably not enough to cause a problem. The voltage changes with vacuum which should confirm its working at there is not a leak in it. I just replaced the booster check valve it was cheap insurance. Haven't been able to drive it yet.

 

[1987 GMC Jimmy]

Oh, no. I meant just leave the gauge on there a bit to see if they leaks down. For my money, the MAP sensor sounds fine even with the frame shifted voltage results. Have we mentioned the throttle shaft yet? Those get play in them and depending on the mileage, they can be a decent vacuum leak. I sent mine to SPR Performance in IL to have them put a bushing in it.

 

[MtBraun]

Oh, no. I meant just leave the gauge on there a bit to see if they leaks down. For my money, the MAP sensor sounds fine even with the frame shifted voltage results. Have we mentioned the throttle shaft yet? Those get play in them and depending on the mileage, they can be a decent vacuum leak. I sent mine to SPR Performance in IL to have them put a bushing in it.

When testing MAP voltages I left the Mityvac attached for about 10 seconds at each level. It held perfectly. I didn't specifically check the throttle shaft, but for as much ether as I've sprayed on the topside of this engine I would think if it were a serious vacuum leak I would have detected it.

Hoping to get a chance to create some logs this weekend and get Dave's feedback.

 

[4WDKC]

Was just rereading this refreshing my memory and wondered what plugs are you running in this engine?

 

[MtBraun]

Was just rereading this refreshing my memory and wondered what plugs are you running in this engine?

Delco CR43TS. What are you running?

@4WDKC

 

[4WDKC]

Think I put r44ts in my truck before the swap, My 406 would sputter and bog till it cleaned up when using the r42lts, I was thinking maybe yours was doing the same thing.

 

[MtBraun]

Think I put r44ts in my truck before the swap, My 406 would sputter and bog till it cleaned up when using the r42lts, I was thinking maybe yours was doing the same thing.

Are you using r44ts or r42lts?

I pulled a couple plugs and they are reading very rich.

 

[4WDKC]

I will have to check what was in my truck till I did a head swap, I tried r42lts in the vette and they were to cold so I went to cr43lts.

 

[Dougnsalem]

Jusy curious- did you get this straightened/figured out?

 

[MtBraun]

@Dougnsalem didn't see your post and it's been a while.

I haven't given up but took a little break as it was so dang cold up here it was tough for me to work on it.

Still the same symptoms, it will start and run but is almost not driveable due to a severe cut out at around 1000-1500 rpms.

One thing I thought of was the vacuum hose from the MAP sensor to the TB is not factory. I just took a 8" piece of new rubber vacuum hose to make the connection. I kept it mounted as close to the TBI as possible.

I'm likely going to replace the MAP even though it tested out ok and probably go after the coil next.

Plugs show pig rich and I've sprayed ether all over and am confident I don't have a vacuum leak.

Tuner Dave W thinks it may be a AE table adjustment needed but I haven't been able to send him any logs. I can't imagine the base tune being so far out of whack the truck would not be driveable.

 

[MtBraun]

Changed out the MAP sensor...no change in symptoms. Probably going to replace the coil next. Yep, just throwing parts at it now.

 

[MtBraun]

So I gave up and took the truck to my mechanic neighbor. He was able to get it to blip a code 42. I have no idea why it threw a code for him and not for me in the hours I have spent troubleshooting this dang thing. Replaced the ignition module, and whala...its drivable!

It does cut/pop slightly if I stab the throttle, but I'm not gonna worry about it. Stabbing the throttle on this build just reminds me how utterly gutless it is.

Plus, now I'm gonna sell it. Changing jobs and moving back to the Sioux Falls area. Got one too many projects and this will allow my son and I to focus on his 84 swb and the 69 F100.