88 350 TBI cold start stumble.

[Steven Petersen]

You're saying the coolant sensor is showing the temperature of the engine is warmer than actual temperature, before you start the engine?

I just checked. Coolant sensor on scanner shows 32. Coolant in top of radiator measures 28. Temp in engine compartment is 24. Garage is 23 and outside is 19.

I can do a cold start here in a bit. Tell me anything to try or to look for on the scammer.

 

[Schurkey]

How are you measuring the coolant in the rad, the engine compartment, and the outside temp?

 

[Steven Petersen]

How are you measuring the coolant in the rad, the engine compartment, and the outside temp?

just a regular weather thermometer. And an AC thermometer stuck into radiator fluid. Like the kind I use to check vent temperatures. I don’t own any specialty automotive thermometers.

 

[Steven Petersen]

I also looked at temps in my other 2 vehicles for comparison. So I know things are pretty close.

 

[Schurkey]

OK. I thought we were onto something, but a difference of four degrees from temp sensor to radiator doesn't seem like enough to cause a problem.

 

[Steven Petersen]

OK. I thought we were onto something, but a difference of four degrees from temp sensor to radiator doesn't seem like enough to cause a problem.

Yeah, my other comments about 34-35 degrees was on a warmer day. I just hadn’t looked when it was colder. The scanner only lets me see 2 lines of data at a time. What should I look at when I cold start it this morning?

 

[Schurkey]

Hmmmm.

I'd be scrolling the whole list, but paying attention most to

TPS, coolant temp, MAP. Is there an intake air temp sensor? I don't think so, but if there is, watch it's response, too.

Can you verify fuel pressure at the same time?

Do you have an AIR pump? Does it switch from exhaust manifold to air cleaner? The '2500 can force a change to verify that it works in the "Functional Tests".

 

[Steven Petersen]

TPS never changes during stumble. Plus I just installed a new TPS yesterday.

Coolant Temp steadily rises, never reacts when there’s a stumble.

Yes it has a functional AIR pump and the diverter works properly.

I will make sure to look at MAP this time.

No air intake sensor.

I have no way to monitor fuel pressure. I have suspected this too.

 

[PlayingWithTBI]

I have no way to monitor fuel pressure.

If you wanna invest ~$116 here's a way to get a gauge and AFPR.

http://www.rvmorsemachine.com/product.htm

You drill a hole in the bottom plate and bend down your MAP vacuum tube, for the thumb wheel.

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Looks like this.

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[Steven Petersen]

Just did a cold start. Still did 3 stumbles within first 20 seconds. Starting coolant temp was 28 on scanner. Watched MAP numbers closely and they constantly move a small amount. No noticeable difference during stumble.

One thing I’ve forgot to mention. When it first starts it around 1125 RPM. It gradually rises to 1200-1250 within the first 10 seconds.