What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

New motor start up problems 1990 suburban 350

K588

K588

1/2 ton status
 Premium
Joined
Feb 19, 2005
Posts
486
Reaction score
162
Location
Westminster,Maryland
I put a New GM L44 crate motor in my 90 suburban first fire ran for a ~minute shut it off. Since then have not been able to keep it running without pumping the fuel pedal.
Truck ran before engine replacement SES light was always on, still on.
When I replaced the motor I remember replacing the following, their may have been more:

-I rebuilt TBI with ac delco kit, I'm hoping I didn't screw this up somehow. I also read somewhere to put the heavier yellow spring in, I'm thinking I didn't need this as the engine is pretty much stock and has a stock fuel pump.
-AC delco EGR valve and EGR solenoid.
-AC delco TPS
-AC Delco oil pressure sending unit
-BWD brand IAC valve
-AC delco plugs C43TS, plug wires,fuel filter, water pump, thermostat
-AC delco oxygen sensor
- standard brand pcv valve
- DUI 12620BK Distributor

-Truck had no Catalytic convertor or air pump when I bought it and open element air cleaner.

Any ideas? I'm now worried about that heavier yellow spring in the tbi. I checked the tbi with a noid light both sides were flashing and it does appear to be spraying not dripping fuel. I'm thinking swap that spring out for whatever the stock one is?

The running good for the first minute has me puzzled, it fires quick but as I said won't stay going without pumping the pedal now.
 
Bought it in 2019 paperwork from Radley Chevrolet Says L-44 and part# 12681430. Its definitely a small block V8. I remember the guy loading it in my truck said they ordered that particular motor a semi at a time. I had to give them my Vin # when I bought it hope they gave me the correct motor.
 
Last edited:
Correct part number. L-31 should be the long block designation.

What happens if you hold the throttle cracked open? Pumping it should not help. No accelerater pump.
 
If I held it all the way open, partial open or took my foot off the pedal dies instantly. I don't understand the pumping keeping it going either.
 
K588 said:
I put a New GM L44 crate motor in my 90 suburban first fire ran for a ~minute shut it off. Since then have not been able to keep it running without pumping the fuel pedal.
Truck ran before engine replacement SES light was always on, still on.
When I replaced the motor I remember replacing the following, their may have been more:

-I rebuilt TBI with ac delco kit, I'm hoping I didn't screw this up somehow. I also read somewhere to put the heavier yellow spring in, I'm thinking I didn't need this as the engine is pretty much stock and has a stock fuel pump.
-AC delco EGR valve and EGR solenoid.
-AC delco TPS
-AC Delco oil pressure sending unit
-BWD brand IAC valve
-AC delco plugs C43TS, plug wires,fuel filter, water pump, thermostat
-AC delco oxygen sensor
- standard brand pcv valve
- DUI 12620BK Distributor

-Truck had no Catalytic convertor or air pump when I bought it and open element air cleaner.

Any ideas? I'm now worried about that heavier yellow spring in the tbi. I checked the tbi with a noid light both sides were flashing and it does appear to be spraying not dripping fuel. I'm thinking swap that spring out for whatever the stock one is?

The running good for the first minute has me puzzled, it fires quick but as I said won't stay going without pumping the pedal now.
Click to expand...

Pull your codes. Just need a paperclip, jumper a and b on the aldl connector with the key on, engine off.

If the check engine light doesn't blink and shut off with key on/engine off, the ECM already "knows" there is a problem and that needs to be resolved first.
 
When I check the codes I get "12 " 3 times in a row. And the SES light stays on when done., like it did before the swap. I should have pulled the codes then.
I'm sure unhooking the battery doesn't let them buildup, but something is draining the battery when it sits- which is farther down my problem list at the moment.
 
You should be able to get your year service manual from the link in my signature, and find the Code 12 diagnostics. 12 is a "normal" code, but engine light on means something is wrong. I've never had to dig into that code, or "SES light constantly on", but the manual should cover it.

Have you checked for pinched and/or disconnected wires? Fairly easy to get them pinched between the bellhousing and block, or squished, etc. If that is fruitless, you can try wiggling and/or disconnecting the ECM connectors. Always good to verify vacuum hoses are hooked up and not cracked or broken too.
 
I have the factory service manuals I'll go over the wires again and revisit it and check for the constant on as I ran into a dead end with no codes.
 
ryoken said:
check your fuel pressure...
Click to expand...
I have an OTC 5630 I bought at some point for something else it has the bike and Schrader valve type of fittings will that work somewhere on a TBI that I don't remember seeing or do I need a OTC 4480 type that test it down by the filter on the frame rail?
 
No schrader fitting on TBI.

Do you have Autozones out there? They "loan" the pressure tester you can use. Personally I do prefer to measure pressure on the frame wherever connectors are, the TBI fittings can be finicky to mess with and as I'm sure you know, mess those up and you can ruin your TBI.

Definitely figure the light issue out. May not solve the problem, but solve what you know is an issue, and hope that fixes the other issues. If it doesn't, at least that problem won't be a factor.
 
I do have autozones and I will get that pressure checked. I was hoping once I got it running I could then deal with the SES light and see if it was throwing some codes.

Is that heavier yellow spring I put in the tbi something I should swap out ? As in the stock fuel pump can't support it?
 
I assume you are talking about the pressure regulator?

TBI pumps at best can put out 14PSI. The spring simply determines the pressure at which it bypasses and lets fuel back to the tank. If the spring was designed for 40PSI, the TBI pump would put out it's max (say, 14PSI if lucky) and never bypass. But since the pump is only capable of 14PSI, the injectors would still be getting 14PSI, which is just under the 13PSI GM said was the upper end of the spec (9-13PSI being the spec).

Now if you put a 40+ PSI pump in there with the higher PSI spring, then you'd probably be over fueling the engine. But if it's a stock TBI pump, highly unlikely.
 
Got it thanks for explaining that, saved me swapping that spring out. Now I feel like the pump may be my issue.
Yes I was talking about the fuel pressure regulator spring.
 
That leads to another thought. If you check fuel pressure, you should know if its the pump OR the hose in the tank. Parts have been relatively garbage for more than 10 years now (Delco and aftermarket) so a whole host of things could be wrong. But pump failure and in-tank hose failure from ethanol are both common with old pump setups, and a problem with either would be seen with a fuel pressure test. I wouldn't think to replace them without doing the test first.

Additionally, while I'm not a "just because" guy (most of my spark plugs are like 20 years old at this point), the last time I dropped my fuel filter to test pressure, a large amount of black crud came out of the filter inlet side as the leftover fuel spilled from it. Either test after the fuel filter, or test where the filter is and just replace the filter with a name brand part from a real retailer, not amazon and ebay, which are awash with chinese fakes.
 
Will do. I bought the truck about 8-10 years ago and I know the tank had been replaced right before I bought it. The sending unit, pump etc not sure. I replaced the filter with an AC delco and a section of new fuel line on Sunday, originally thinking that was the main problem . It did spill out some nasty gas and when I cut it open was very dirty.
 
I haven't seen much writeups on fuel filter quality. For oil filters Wix are pretty good last I saw, I'd expect their fuel filters to be of adequate quality too.

I'd take Wix over Delco at this stage, but if all I could get was Delco, and it came from someplace like Napa or Autozone, etc., I wouldn't worry too much about running it. The real problems are just crappy aftermarket parts (cheap) and the fakes that are good enough to fool 99% of the buyers. Without two identical components side by side, with a known OEM being one of them, it's almost impossible to know what is fake, and what is OEM modification as time goes on.
 
So I checked the fuel pressure, marks on gauge started at 4 psi I barely got 1 to 2 psi. Pump is coming on . Drained the fuel out of the tank tonight.

My questions , gauge was one mark below full I maybe got out 27~ gallons, I thought I remembered it being a 40 gallon tank. Gauge did read E when I was done siphoning. Should I replace the entire sending unit when I drop it to replace the pump? If so what is a good brand?

Should I replace the pump with the later Ac delco EP381 pump ? Or just the stock pump?

Is there anything else I would need to have there when I drop it, to replace at the same time inside the tank. Fuel pickup screen/ sock etc?
 
You must log in or register to reply here.

Latest Posts

Top Bottom